Roth Williams 2010

Contents

1RWISO Journal | September 2010

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Volume 2, No. 1, September 2010

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57Jina Lee Linton, DDS, MA, PhD, ABO ■ Woneuk Jung, DDSThe Effect of Tooth Wear on Postorthodontic Pain Patients: Part 2

Dori Freeland, DDS, MS ■ Theodore Freeland, DDS, MSRichard Kulbersh, DMD, MS, PLC ■ Richard Kaczynski, BS, MS, PhDComparison of Maxillary Cast Positions Mounted from a True Hinge Kinematic Face-Bow vs. an Arbitrary Face-Bow in Three Planes of Space

Michael J. Gunson, DDS, MD ■ G. William Arnett, DDS, FACDCondylar Resorption, Matrix Metalloproteinases, and Tetracyclines

Byungtaek Choi, DDS, MS, PhDHinge Axis: The Need for Accuracy in Precision Mounting: Part 2

Ryan K. Tamburrino, DMD ■ Normand S. Boucher, DDSRobert L. Vanarsdall, DDS ■ Antonino G. Secchi, DMD, MS The Transverse Dimension: Diagnosis and Relevance to Functional Occlusion

Wesley M. Chiang, DDS, MS ■ Theodore Freeland, DDS, MSRichard Kulbersh, DMD, MS, PLC ■ Richard Kaczynski, BS, MS, PhDEffect of Gnathologic Positioner Wear on Maximum Intercuspation CR Disharmony

Andrew Girardot, DDS, FACDPhysiologic Treatment Goals in Orthodontics

Letter from RWISO President, Samuel B. King, DDS, MS

Letter from Editor-In-Chief, Thomas Chubb, DDS

News from the Roth Williams Teaching Centers

The Roth Williams Legacy Fund (RWLF) — Committee Report

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RWISO JOURNALSEPTEMBER 2010 VOL. 2, NO. 1

EDITOR IN CHIEFDr. Thomas K. Chubb

EXECUTIVE DIRECTOR/ADVERTISING SALESJeff Milde

MANAGING EDITORAnne Evers

CREATIVE DIRECTORSBrad Reynolds (www.integralartandstudies.com)

RWISO Journal is published by the Roth Williams International Society of Orthodontists. Copyright © 2010 RWISO. All Rights Reserved.

ISSN 2154-4395 (print)ISSN 2154-4409 (online)

Reproduction whole or in part in any form or medium without express written permission of RWISO is prohibited. Information furnished in this journal is believed to be accurate and reliable; however, no respon-sibility is assumed for inaccuracies or for the information’s use.

Postmaster:Send address changes to RWISO1712 Devonshire RoadSacramento, CA 95864

RWISO JournalRoth Williams International Society of Orthodontists1712 Devonshire RoadSacramento, CA 95864 USAPhone: 916-270-2013Fax: [email protected]

We welcome your responses to this publication. Please send comments, subscriptions, advertising and submission requests to: [email protected]

The Roth Williams International Society of Orthodontics is the embodi-ment of a philosophical and technological transformation: addition of physiologic to anatomics from a foundation of function and esthetics.

BOARD OF DIRECTORS

PresidentDr. Sam King6460 Far Hills AvenueCenterville, OH 45459 [email protected]

President ElectDr. Douglas Knight, DMD3210 Westport Green PlaceLouisville, KY 40241 [email protected]

Vice PresidentDr. Renato CocconiVia Traversante, San Leonardo 143100 Parma, [email protected]

SecretaryDr. Eunah ChoiSomang BD 2F, 907-1 Bangbae 1 DongSeocho GuSeoul, 137-842 [email protected]

TreasurerDr. John F. Lawson, MS2460 Nwy 63 NorthRochester, MN 55906 [email protected]

Immediate Past PresidentDr. Darrell Havener 1420 West Canal Court,Suite 200Littleton, CO 80120 [email protected]

Executive DirectorJeff Milde1712 Devonshire RoadSacramento, CA 95864 [email protected]

COUNCIL MEMBERS

Region I - Asia

Dr. Satoshi Adachi #202, 5-11-8 MinohMinoh, Osaka 562-0001 [email protected]

Dr. Eunah ChoiSomang BD 2F, 907-1 Bangbae 1 DongSeocho GuSeoul, 137-842 [email protected]

Region II - Europe

Dr. Claudia AichingerBillrothstr. 58Vienna, A-1190 [email protected]

Dr. Renato CocconiVia Traversante, San Leonardo 1 43100 Parma, [email protected]

Dr. Domingo Martin Plaza Bilbao 2-2A San Sebastian, 20005 Spain [email protected]

Region III - USA, Canada

Dr. Ramon Marti, MSC281 Oxford Street E.London, Ontario N6A 1V3 [email protected]

Region IV - South America

Dra. Solange M. deFantini, MSDAl Janu 176 cj 42Sao Paulo, SP 01420-002 [email protected]

Dra. Marisa Gianesella BertolacciniRua Tabapuã, 649 - Conj. 83Itaim Bibi, São Paulo, SP, 04533-012 Brazil+11- 505-25417 [email protected]


Letter from the President

Samuel B. King, DDS, MS RWISO President

The world is changing rapidly. Technology is enabling us to do things never before possible. Orthodontics is changing too. New technologies, evolution of procedures, ease in obtaining information are just a few of the things that are advancing the orthodontic profession. The Roth Williams International Society of Orthodontists continues to evolve to provide the very best for our patients, but as we move forward with these new technologies, we are ever mindful of our treatment goals and the standards of our philosophy. The RWISO Journal embodies our commitment to remain true to our treat-ment goals and the standards of our philosophy. As orthodontic treatment changes, it is our duty to ensure, through evidence-based research, that new techniques and modalities achieve our goals and maintain our standards. Our Journal serves to educate our global organization about these advancements so that our members can confidently deliver the Roth Williams goals and standards to their patients. The Roth Williams International Society of Orthodontists is in the midst of an exciting time. Today we are able to treat our patients better than ever be-fore with exciting new advancements in our profession. It is truly a great time to be part of the Roth Williams International Society of Orthodontists. Respectfully,

Samuel B. King, DDS, MS RWISO President

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Letter from the Editor

Thomas Chubb, DDSEditor-In-Chief of RWISO Journal

I would first like to thank all the authors in this year’s Journal for the amount of time and energy they devoted to giving us another first class issue. They are the lifeblood of the RWISO Journal. I know the authors would be interested in your feedback. Their e-mail addresses are listed on their articles, so please contact them with any comments you might have. I apologize to any author whose submission did not make it into this issue. We are already working on the next issue, which we hope will come out between now and the next meeting.

I would like to thank Anne Evers, our managing editor, and Irene Elmer, our copy editor, for all their hard work and professionalism. Many of the authors have felt the sting of Irene’s sharp pen and the exacting revisions they both required. Their many hours of hard work were needed to bring this issue to fruition. I would also like to thank all our sponsors who contributed generously to help publish this issue and to Jeff Milde for all his logistical support.

After reading the reports from the Roth Williams regional directors, I was struck by the level of involvement in education to which this group has devoted itself. Unfortu-nately, we meet only once a year to reconnect with our far-flung colleagues to rein-vigorate and recommit ourselves. I see the RWISO Journal as having a vital function in sharing information for those members who attend the annual meeting and, more importantly, for those who cannot. It gives us something to hand to our non-Roth Williams orthodontists and dental colleges to show the type of research and clini-cal results that is being produced. The articles is this issue are diverse and some are groundbreaking.

You will note this issue of the Journal is mostly articles with only one case report. Oddly, we have had very few case reports submitted. My feeling is that the RWISO Journal needs a better balance of articles and case reports. Over the years I have seen many outstanding cases presented at the RWISO meetings. One of the strengths of our group has always been in showing well-treated cases with beautiful finishes. However, more importantly, these cases have one more thing in common: stable joints with good function of the teeth and joints. And how do we know this? We know because we evaluate our results with the use of centrically mounted models, condylar record-ing systems, and TMJ scans. I believe it is the documentation of our orthodontic cases that defines our group. Any journal can show a pretty orthodontic finish. It is another thing to show all the records, the treatment planning, and then the clinical execution and a measured outcome of a challenging case. Since this Journal will be seen by many non-Roth Williams orthodontists, I think it is critical we show more of our clinical orthodontic work in this journal.

I hope to see this Journal grow and become a vital part of our organization as it is a

reflection of who we are and what we believe in.

Thomas Chubb, DDSEditor-in-Chief [email protected]

Dr. Thomas Chubb | Letter from the Editor



ARGENTINA We are pleased to announce that in May of this year we began the Roth Williams FACE (The Foundation for Advanced Continuing Education) Course in cooperation with the Catholic University of Argentina. Dr. Oscar Palmas, Dr. Guillermo Ochoa and Dr. Eduardo Rubio (surgeon)were he instructors for this course. They had the honor of working alongside Dr. Domingo Martin and Dr. Jorge Ayala. The highlight was a lecture given by Dr. Martin on interdisciplinary treatment.

Many feeder courses were developed this year in different provinces, including Salta, Jujuy, Rio Gallegos and Santiago del Estero. More than 300 hundred students were taught about the Roth Williams philoso-phy. In September 2011, Dr. Jorge Ayala will give a feeder course entitled “Biomechanical Treatment in Roth Philosophy.”

For next year we are planning a Roth Williams FACE national meeting in Jujuy, an Argentinean province. The Roth Williams Center Argen-tina will participate in the Mendoza Society Orthodontic Meeting in September. Dr. Oscar Palmas will give a lecture on self-ligation and micro-screw in Roth Philosophy.

We are very happy to see the poster contributions for the Rome meet-ing from our Roth Williams students. We would also like to take this opportunity to congratulate the Journal on its second issue. We encour-age you all to continue working!!

Dr. Oscar PalmasDirector, Roth Williams Center Argentina

BRAZIL The Brazilian Center began a new CCO group in June 2009. It has attracted students from the northwest to the southwest of Brazil. Dr. Fantini has been traveling to various places in Brazil to spread the Roth Philosophy. She has been teaching courses and has even lectured at an advanced-level specialization course, where her talks about the Philosophy have become a tradition. In October 2010, the SPO meeting, which is the most important meet-ing in Latin America, will take place in Brazil. Dr. Fantini will speak on Roth’s Philosophy: multidisciplinary treatment of skeletal class II malocclusion with bilateral condylar degeneration and generalized root resorption. Since 2009 four abstracts have been published in conference proceed-ings, three articles have been accepted in orthodontic magazines, and two book chapters have been dedicated to the Roth Philosophy. Dr. Fantini has participated in 10 MA, PhD, and qualifying examinations as an examiner, enhancing the concepts of the Roth Philosophy. For a complete list of the articles and abstracts, please contact the RWISO office. The study group founded in the beginning of 2008 remains active with reunions every 2 months. We believe we have found an interesting for-mula to deepen the knowledge of those who took the CCOs. At each

group meeting, our program includes 3 activities—a participant pre-sentation on a given theme, a clinical case presentation and discussion, and a talk on a new topic of current interest. This format has made the study group very popular.

We plan to start a new CCO group in June 2011. Finally, we are considering organizing a memorial meeting for all South America in São Paulo in November 2010.

Dra. Marisa Gianesella BertolacciniDirector, Roth Williams Center Brazil

CHILE

As is traditional, our educational activities have remained very active through continuing courses, 2- or 3-day courses, and participation in various meetings. We are currently offering long-term courses in Mexico (two), Argentina, Paraguay, and Chile with a total of 170 students. In 2009 thru 2010 we held 34 courses. In 2010 we will offer two new continuing courses, one in Michoacán, México, and the other one at the Universidad de Tucumán, Argentina. A course in Brazil, to be held in collaboration with Dr. Solange Fantini, is also being organized.

Drs. Jorge Ayala and Gonzalo GutierrezDirectors, Roth Williams Center Chile

JAPAN

We are pleased to announce that we now have 45 members. Members are doctors who have graduated from the 2-year course and have also presented cases with stable and repeatable jaw position. Each year we hold an annual meeting where each participant shows his/her cases treated according to the Roth philosophy. Along with the annual meet-ing, we are now preparing for the 15th anniversary meeting in Tokyo on November 28-29. This meeting is open to all interested doctors. We are expecting a great attendance. We of course welcome RWISO members from all over the world.

The ninth 2-year course is steadily ongoing and session 5 was held for 5 days in June, and featured Dr. Jorge Ayala from Chile as a special instructor. The 14th basic course will be held in the fall.

Dr. Kazumi IkedaDirector, Roth Williams Center Japan

continued on next page...

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KOREA In March 2010 the eighth Roth Williams International Seminar was held. The 10 participants in the course were instructed by Drs. Byung-taek Choi, Eunah Choi, and Gyehyeong Lee. All participants enthusias-tically took part in the course. As visiting professors, Drs. Byungtaek Choi and Eunah Choi lectured on the Roth philosophy to the residents of the Department of Ortho-dontics at the Seoul National University Dental Hospital. The lectures were held weekly during the month of June 2010. The Roth Williams Center Korea has been encouraging our members to contribute to the Roth Williams Legacy Fund. We expect a desirable outcome by the 2010 annual meeting in Rome.

Dr. Eunah ChoiDirector, Roth Williams Center Korea

SPAIN Without any doubt 2009 was a great year for RW Spain/Portugal. Concerning the RW 2-year course, this year we finished group number 10 (26 students) and we started group number 11 (28 students). The 2-year course has truly grown to be a comprehensive orthodontic course. We now have three full-time teachers who come to every session and not only help in the clinic but also present as teachers. They are Drs. Alberto Canabez from Barcelona, Eugenio Martins from Portugal, and Iñigo Gomez from Bilbao. All three of them have contributed to the excellent quality of the RW course. Apart from these full-time teachers, we have also incorporated into our courses experts in the different fields of dentistry, who have come and taught differ-ent sessions. They are Dr. Iñaki Gamborena, prosthodontist, Drs. Jon Zabalegui and Iñigo Sada, periodontists, Dr. Dave Hatcher, radiologist, Dr. Borja Zabalegui, endodontist, Dr. Renato Cocconi, orthodontist, and Dr. Mirco Raffaini, surgeon. All of these teachers have given the RW courses a truly interdisciplinary approach, which is what FACE promotes worldwide. Another important aspect of 2009 that has been fundamental in making RW a truly interdisciplinary course is the fact that we have organized two different courses, Bioesthetics with Dr. Ken Hunt and Dr Alejandro James, and Orthognathic Surgery with Dr. Lucho Quevedo. Many of our former students have signed up for the courses, and this has given them a greater understanding of the importance of incor-porating both disciplines into our interdisciplinary approach. But we cannot forget that with Osteoplac now organizing and promoting our courses they have become truly professional, and without this support we could have never reached the status that we now enjoy.

Dr. Domingo MartínDirector, Roth Williams Center Spain and Portugal

UNITED STATES

New and exciting things are happening within the Advanced Educa-tion in Orthodontics (AEO) group. In June of 2010, Group VIII will have their graduation. Group VIII is the largest class, with 25 doctors. A total of 125 doctors have finished the rigorous seven sessions. The directors have been extremely uplifted by the positive responses given by the graduates as to their overall educational experience. Comments like this are the usual: “Keep up the good work. I thank you daily in the back of my mind for telling me I needed to take this course and that I would be a better orthodontist. You guys were absolutely right and as challenging as our profession is and as smart as our colleagues are, I feel light years ahead of them and my GP’s thank you.” Ben.

The course is continuing to improve and evolve without sacrificing any of the Roth Williams basics. Techniques such as the true horizontal hinge axis mountings combined with true horizontal hinge axis 3-D imaging have been introduced to improve accuracy of diagnosis and treatment planning. In the past, AEO was successful in improving the Visual Treatment Options (VTO) both in ease of use and in teaching technique. Now the course incorporates the latest in 3-D technology.

The directors have been instrumental in developing software that en-hances the efficiency of orthodontic diagnosis and treatment planning. The next step is to develop 3-D software that is based on the true hinge axis. This is being handled by Dr. Robert Frantz.

Dr. Andrew Girardot is responsible for editing and publishing the long-awaited Roth Williams Philosophy textbook. Because of the substantial commitment required for this important project, Andy will not be teaching formally until his work on the book is complete.

The true standard wide archform (SWA) system that Dr. Roth developed is continuing to evolve. With the help of the Head of Product Develop-ment at GAC, Tom Macari, and AEO, improvements to the bracket are in the works.

The teaching techniques developed at AEO are evolving as well. With the advent of new computer technology, many new and exciting things will be happening in the next year.

The Roth Williams USA center has a new home base. Due to an excel-lent opportunity afforded us by Dr. Carlos Navarro, AEO will be mov-ing to Houston, Texas. So in October of 2010, Group IX will travel to Texas for the new class. The new facility will have adequate space for teaching the total Roth Williams experience. The clinical, laboratory, and lecture will now be in one location. This location is close to many fine restaurants and entertainment.

Drs. Andy Girardot, Bob Frantz, and Ted FreelandDirectors, Roth Williams Center USA

URUGUAY Once again, it is a pleasure for the Roth Williams Center Uruguay for Functional Occlusion (RWCUFO) to be present in our Journal. We would like to inform you that finally in December 2009, our 3-year course started in the Faculty of Odontology, Catholic University of Montevideo, Uruguay. The first three sessions have been completed, with a total of 13 participants. We are having real success with the contribu-tions of our friends and outstanding speakers from all over the world.



In addition, three 8-hour courses were scheduled in April, August, and December 2010. Presentations include Dr. Roth’s Philosophy: the importance of the condyle setting in the fossae:physiological principles for neuromuscular deprogramming, by Dr. Guillermo Ochoa; Treat-ment planning according to Roth’s Philosophy, by Dr. Oscar Palmas; and Evidence-based Roth’s Philosophy and its application in multidis-ciplinary treatments, by Dr. Domingo Martín. Dr. Martín will also be giving a 4-day course for all the specialists related to orthodontics. To know more about our courses, please visit the Web page www.ucu.edu.uy/Odontologia, or contact us by e-mail at [email protected]. Our group is concerned about research. To address this concern, we are encouraging our students to make a weekly commitment to our study group. We are working hard in order to achieve the best results.

Dr. Daniela Domínguez Di PriscoDirector, Roth Williams Center Uruguay

Scenes from RWISO 200916th Annual Conference, Boston, MA

8 Roth Williams Legacy Fund

Fund-Raising Progress

As of June 1, 2010, $208,650 had been donated to the Roth Williams Legacy Fund (RWLF).

Of the money donated, $178,650 has been given to the general research and education portion

of the fund and $30,000 has been specifically donated to the Roth Williams textbook portion

of the fund.

As of June 1, 2010, $107,290 had been pledged to RWLF but had not yet been donated.

RWLF is proud of the progress that has been made to date. Due in part to the worldwide

economic recession, we realize that our campaign goal of $1 million in 5 years may not be

attainable. However, we truly believe that the goal of $1 million will be reached as RWISO

continues to grow in stature and respect. The future is bright for the Roth Williams Philosophy

of goal-directed interdisciplinary patient care.

A special thanks to Drs. Jeff McClendon and Milt Berkman for giving the Coordinating Orthodontic and Restorative Efforts

(CORE) course and raising almost $9,000 for RWLF. As of July 2010, the course will have been given four times.

2009 Boston Meeting and Journal

At the RWISO International meeting held in Boston, Massachusetts, in May 2009, the Committee was pleased with the

membership’s response to the RWLF fund-raising campaign for the general endowment fund and for the Roth Williams

Philosophy textbook fund. The publication of the first issue of the RWISO Journal, in May 2009, came to fruition in part

because of a grant from the RWLF general endowment fund for $14,000. As Dr. Domingo Martín said in the first issue of

the Journal, “I cannot forget it was Dra. Anka Sapunar who first founded a journal for this group, and we must all be very

grateful to her for the great job that she did. This is a continuation of what she started. Muchas gracias, Anka!!!”

The renewal of the Journal would not have been possible without the seed money from RWLF. This is just one of the many

ways that RWLF is able to fulfill its mission to advance the scientific and clinical benefits of the Roth Williams Philosophy

of goal-directed interdisciplinary patient care. What a great moment for the RWISO membership! For RWLF it was a signifi-

cant first step, because it demonstrated the important role of an endowment fund in the future growth and longevity of an

organization and a philosophy of patient care. RWLF and the RWISO membership are looking forward to the second issue

of the RWISO Journal at the Rome Conference with great anticipation.

Research Evaluation and Approval Committee (REAC)

The RWLF Committee’s initial major efforts have been directed toward fund-raising, and toward gaining the trust and confidence of the RWISO membership. Now that 30% of the $1 million goal has been pledged or donated, the Com-mittee is ready for a new endeavor—to develop research grant evaluation, approval, and funding. One of the mission statements of RWLF is “partial or full support of research projects that lead to publication of scientific and clinical papers in peer-reviewed international journals.” The Committee is pleased to announce that two research grants have been approved and are in the process of being funded by RWISO/RWLF.

The Roth Williams Legacy Fund Committee Report

Dr. Milton D. Berkman, Chairman RWLF

Dr. Milton D. Berkman, Chairman, RWLF


Drs. Edson Illipronti and Solange Fantini from Brazil were awarded a grant for a research project entitled Evaluation of functional morphology in children with unilateral posterior crossbite before and after rapid maxillary expansion. The grant is to pay in part for MRI studies. The grant is for $16,000 over a 3-year period. Drs. Carol Weinstein and Sigal Bentolila Weiner from Chile were awarded a grant for a research project entitled De-gree of apical root proximity, periodontitis, and root resorption of the upper canine and first bicuspid found in sample of Roth prescription-treated orthodontic cases using cone beam radiography compared to panoramic radiography. The grant is to pay in part for cone beam radiography studies. The grant is for $3,000 over a 3-year period.

Donation and Pledges

Donations to RWLF can be made in the following ways:

1. Professional Courtesy/Grateful Patient. Persons to whom you offer orthodontic services as a courtesy are invited to demonstrate their appreciation by making a contribution to RWLF in your name. 2. Case for the Future of the Roth Williams Philosophy. Doctors can donate one new case as a “case for the future” by paying the fee to RWLF. 3. Doctors giving courses or lectures can donate a portion of the honorarium or course fees to RWLF. 4. Donations can be made in memory of, or in honor of, a colleague, friend, relative, or parent.5. Or just make a donation because of what the Roth Williams Philosophy has meant to your professional life

Donations can be designated for the general research and education fund or for publication of the Roth Williams Philosophy textbook.

For more on how to donate, visit the RWISO Web site at www.rwiso.org.

RWLF Committee

Thank you to those individuals who serve on the Legacy Fund Committee.

Milton D. Berkman, Chairman RWLF Peggy Brazones Alan Marcus Domingo Martín Jeff Milde, Executive Director RWISO Joe Pelle Straty Righellis, Chairman REAC Manny Wasserman David Way

10 Legacy Fund Donors

Roth Williams Legacy Fund Donors

Tribute to Donors

We thank all of our loyal and faithful donors for their support of the Legacy Fund. Below, we pay tribute to those donors who have given from January 1, 2006, through June 21, 2010.

Platinum (10,000 - $49,999) Dr. Milton D. Berkman Dr. Domingo Martin Dr. Straty Righellis Dr. Carl Roy Dr. Manny Wasserman Dr. Robert E. Williams

Gold Circle ($5,000 - $9,999) Dr. Margaret Brazones Dr. Byungtaek Choi Dr. Andrew Girardot Dr. Darrell Havener Dr. John Lawson Dr. Jina Linton Dr. Jeffrey McClendon Dr. James Sieberth Dr. Wayne Sletten Dr. David Way GAC International

Silver Circle ($1,000 - $4,999) Dr. Terry Adams Dr. Claudia Aichinger Dr. Robert Angorn Dr. Joachim Bauer Dr. Patricia Boice Dr. Renato Cocconi Dr. Frank Cordray Dr. K. George Elassal Dr. Keenman Feng Dr. Michael Goldman Dr. Frank Gruber Dr. David Hatcher Dr. Kazumi Ikeda Dr. John Kharouf Dr. L. Douglas Knight Dr. Young Jun Lee Dr. Gerald Malovos Dr. Alan Marcus Dr. Ramon Marti Dr. Roger Pitl Dr. Paul Rigali Dr. Nile Scott Dr. Sean Smith Dr. Katsuji Tanaka Reliance Orthodontic Products

Bronze Circle ($1 - $999) Dr. Hideaki Aoki Dr. George Babyak Dr. Mary Burns Dr. Dara Chira Dr. Tom Chubb Dr. Warren Creed Dr. Graciela de Bardeci Dr. Chieko Himeno Dr. Takehiro Hirano Dr. Akira Kawamura Dr. Mi Hee Kim Dr. Yutaka Kitahara Dr. Shunji Kitazono Dr. Felix Lazaro Dr. N. Summer Lerch Dr. Ilya Lipkin Dr. George Marse Jeff Milde Dr. Kouichi Misaki Dr. Hideaki Miyata Dr. Yo Mukai Dr. Yoshihiro Nakajima Dr. Joseph Pelle Dr. Akiyuki Sakai Dr. Atsuyo Sakai Dr. Hidetoshi Shirai Dr. Motoyasu Taguchi Dr. Naoyuki Takahashi Dr. Hiroshi Takeshita Dr. Yasoo Watanabe Dr. Benson Wong Dr. Koji Yasuda Dr. Yeong-Charng Yen

Estate Planning Dr. Charles R. de Lorimier Dr. Donald W. Linck, II

Friends of Roth Williams Advanced Education in Orthodontics Jewish Communal Fund T&T Design Lab (Japan) Timothy McCarthy

Pledge CircleThank you to these donors who have pledged donations to the Legacy Fund over multiple years.

Dr. Satoshi Adachi Dr. Scott Anderson Dr. Jorge Ayala Dr. Milton Berkman Dr. Margaret Brazones Dr. Warren Creed Dr. Robert Good Dr. Mila Gregor Dr. Tateshi Hiraki Dr. Maria Karpov Dr. Mi Hee Kim Dr. Masako Komatsu Dr. Jina Lee Linton Dr. Ilya Lipkin Dr. Dave Livingston Dr. Yuci Ma Dr. Alan Marcus Dr. Ramon Marti Dr. Joseph M. Pelle Dr. Paul Rigali Dr. Nile Scott Dr. Wayne Sletten Dr. Manny Wasserman Dr. Benson Wong Dr. Yeong-Charng Yen Dr. Michael Yitschaky


The Transverse Dimension: Diagnosis and Relevance to Functional Occlusion

Summary

Ryan K. Tamburrino, DMD ■ Normand S. Boucher, DDS ■ Robert L. Vanarsdall, DDS

■ Antonino G. Secchi, DMD, MS

IntroductionThe goals of orthodontic treatment are well established

for static and functional occlusal relationships. In order

to achieve Andrews’ six keys to normal occlusion for the

dentition,1 the jaws must be optimally proportioned in

three planes of space and positioned in CR. Orthodontists

have a multitude of cephalometric analyses available to di-

agnose skeletal and dental variations of the sagittal and

vertical dimensions.2–6 Several analyses for the transverse

dimension are also available,3,6,7 but these analyses are not

well accepted as forming part of a traditional orthodontic

diagnosis.

In the sagittal dimension, when the jaws do not relate

optimally, the dentition will attempt to compensate, resulting

in excessively proclined or retroclined anterior teeth. In the

transverse dimension, when the jaws do not relate optimally,

usually due to a deficiency in the width of the maxilla,7,8 the

teeth will erupt into a crossbite or reconfigure their incli-

nations to avoid a crossbite. This compensation typically

involves lingual tipping of the mandibular posterior teeth,

which are then described as being excessively negatively in-

clined. In addition, the maxillary posterior teeth are tipped

facially. These teeth are then described as being excessively

positively inclined (Figure 1).

Transverse Deficiency and CR/CO DiscrepancyIn the prosthodontic literature, these transverse tooth com-

pensations have been graphically illustrated with a cross-

arch arc constructed through the buccal and palatal cusps of

Much focus of orthodontic diagnoses has been placed on the sagittal and ver-

tical dimensions. However, a proper evaluation of the transverse dimension

must also have equal importance. Research has shown that interferences from

an exaggerated curve of Wilson due to a maxillary transverse deficiency play

a role in centric relation (CR)/central occlusion (CO) discrepancies, adverse

periodontal stresses, and craniofacial development. This article illustrates

three scientifically validated methods for evaluating the transverse dimension:

Ricketts’ P-A cephalometric analysis, Andrews’ Element III analysis, and the

University of Pennsylvania Cone-Beam CT transverse analysis. The aim is to

show methods using traditional cephalometry, study models, and cone-beam

computed tomography, not to compare one method to another. The reader

may then choose to use the method that is most appropriate for his practice.

Ryan K. TambuRRino, [email protected]■ Clinical Associate—Univ. of Penn. School of Dental Medicine, Dept. of Orthodontics

noRmand S. boucheR, ddS■ Clinical Associate Professor— Univ. of Penn. School of Dental Medicine, Dept. of Orthodontics

RobeRT L. VanaRSdaLL, ddS■ Professor and Chair— Univ. of Penn. School of Dental Medicine, Dept. of Orthodontics

anTonino G. Secchi, DMD, MS■ Assistant Professor of Orthodontics, Clinician Educatorand Clinical Director—Univ. of Penn. School of Dental Medicine, Dept. of Orthodontics

Figure 1 Example of excessive tooth angulations.

For complete contributor information, please see end of article.

12 Tamburrino et al | The Transverse Dimension: Diagnosis and Relevance to Functional Occlusion

the maxillary molars. This is known as the curve of Wilson.

With excessive inclination of the maxillary molars to com-

pensate for insufficient maxillary width, the curve of Wilson

is greatly exaggerated, and the palatal cusps are positioned

below the buccal cusps (Figure 2).

Many articles that describe the impact of CR/CO dis-

crepancies on occlusion focus on how these discrepancies

affect diagnosing the sagittal and vertical dimensions. The

literature has suggested that the “plunging” palatal cusps

shown in Figure 3 are often the primary contacts that in-

duce vertical condylar distraction on closure from CR. From

a seated condylar position, the patient may fulcrum off the

premature contacts of the terminal molars to obtain the

maximal intercuspal position. The Panadent Condylar Posi-

tion Indicator (CPI) and the SAM Mandibular Position In-

dicator (MPI) graphically identify this vertical component of

condylar distraction.9-12

Figure 2 An exaggerated curve of Wilson (note palatal cusps below buccal cusps).

Figure 3 Note plunging palatal cusps and extreme curve of Wilson on molars of an arch that was expanded

with arch wires and brackets only.

According to McNamara and Brudon,13 “the orientation of

the lingual cusps of the maxillary posterior teeth… often lie[s]

below the occlusal plane… This common finding in patients

with malocclusions often is due to maxillary constriction and

subsequent dentoalveolar compensation in which the maxillary

posterior teeth are in a slightly flared orientation.” The results

of a study by McMurphy and Secchi14 indicate that vertical dis-

traction of the condyles in CR/CO discrepancies can be related

to an exaggerated curve of Wilson, secondary to a transverse

deficiency of the maxilla. These authors conclude that, in the

absence of a posterior crossbite, the plunging palatal cusps and

exaggerated curve of Wilson become the fulcrum point for the

vertical condylar distraction from CR to maximum intercuspa-

tion. Furthermore, extrapolation of this statement suggests that

if the transverse skeletal dimension is normalized, the curve of

Wilson is flattened, and the arches are coordinated, an impor-

tant component of the CR/CO discrepancy is eliminated.

Transverse Deficiency and Working/Nonworking InterferencesIt has been a prosthetic maxim that an exaggerated curve of

Wilson increases the potential for working and non-working

side interferences. Studies have shown that posterior occlusal

contacts or interferences are linked to increased masticatory

muscle activity.15,16 In studies where these interferences have

been removed, it has been demonstrated that the activity of the

closing musculature is reduced.16,17 In addition, a study that ar-

tificially created non-working interferences reported increased

muscle activity.18 These results suggest that it is prudent to nor-

malize the transverse jaw relationship and flatten the curve of

Wilson to eliminate the potential for excursive posterior inter-

ferences or contacts.

Transverse Deficiency and the PeriodontiumHerberger and Vanarsdall19 have shown an increased risk for

gingival recession in the orthodontic patient with a narrow

maxilla when the skeletal transverse deficiency is camouflaged

with dental expansion. The envelope of treatment in the trans-

verse, with expansion of only the dentition, is more limited than

the envelope of treatment in the sagittal dimension.20 Due to the

constraints of the thin layer of cortical bone of the alveolus, as

shown in Figure 4 [see next page], very little tooth movement

needs to occur before the roots are fenestrated, the volume of

buccal alveolar bone is reduced, and, with thinning gingival tis-

sues, the risk of gingival recession increases.

In recent studies, Harrell21 and Nunn and Harrell22,23 have

shown that the elimination of working and nonworking interfer-

ences enhances the long-term periodontal prognosis in patients

susceptible to periodontal disease. Therefore, normalizing the

transverse jaw relationship to eliminate an exaggerated curve


of Wilson and nonworking interferences would be beneficial

for adult patients who are periodontally at risk, and might

prophylactically reduce the risk for younger patients.

Transverse Deficiency and the AirwayRicketts’ description of “adenoid facies”24 also suggests a re-

lationship between a constricted nasopharyngeal airway and

a narrow maxilla. Ricketts states children with any impair-

ment of the nasal passages become predominantly mouth

breathers. Since the tongue is positioned in the floor of the

mouth to allow airflow, it cannot provide support to shape

the developing palate; thus pressure from the circumoral

musculature acts unopposed. The palate is narrowed, and

an exaggerated curve of Wilson develops upon tooth erup-

tion. Because the tongue is positioned low in the mouth, the

patient may also develop a retruded, high-angle mandibular

shape, which can increase the risk for sleep apnea.25 An ex-

ample of adenoid facies is shown in Figure 5.

Figure 4 Patient with gingival recession due to orthodontic treatment in the presence of an undiagnosed severe skeletal

transverse discrepancy. Note minimal alveolar bone on the buccal surface of the maxillary molars.

Figure 5 A teenager who had nasopharyngeal airway impairment during growth and development. The images show the facial,

dental, skeletal, and airway presentation upon growth cessation.

In one recent study,26 patients with transverse deficien-

cies due to a narrow maxilla who were treated with rapid

palatal expansion, showed an increase of 8% to 10% in the

volume of the upper airway. In another study, 27 patients with

dental posterior crossbites who were treated with palatal ex-

pansion also showed an increase in the volume of the upper

airway. Oliveria de Felippe, et al28 found that palatal expan-

sion decreased nasal resistance and improved nasal breath-

ing. While additional research in this area is certainly needed,

the current literature suggests that any improvement in the

volume of the airway, as an effect of palatal expansion to

optimize the transverse dimension of the jaws, may greatly

benefit overall growth and development.

Methods of Transverse DiagnosisWith a transverse deficiency due to a narrow maxilla, the

temporomandibular joints, musculature, periodontal tissue,

and airway can be adversely affected in the susceptible pa-

tient. Our goal as orthodontists should be to develop skeletal

relationships and a functional occlusion that are as close to

optimal as possible, to lessen the role that any discrepancies

of the occlusion would play in exacerbating the detrimen-

tal effects to the joints, periodontium, or dentition. In order

to achieve this a correct skeletal and dental diagnosis in all

three planes of space is mandatory.

In this section, we present three different methods for

diagnosing the transverse dimension—one using traditional

cephalometry, one using dental casts, and one using cone-

beam CT (computed tomography). We do not endorse any

one of these methods over the others; our purpose here is

simply to describe all three methods, so that readers will be

able to incorporate a transverse skeletal diagnosis into their

practice, no matter what level of technology is available.

Regardless of which of these methods one chooses, the doctor

must keep optimal treatment goals in mind as a rationale for

normalizing the transverse dimension (Figures 6 and 7).

Figure 6 Goals for normalizing the transverse dimension.


Ricketts’ P-A AnalysisIn 1969, Ricketts introduced analysis of the transverse skel-

etal dimension as part of his method of cephalometric di-

agnosis.3 His method uses the frontal, or posteroanterior

(P-A) cephalogram, and is based on the dimensions of the

jaws compared to a table of age-adjusted normative values.

The premise of the analysis is based on locating two skeletal

points to determine maxillary width and two additional skel-

etal points to determine mandibular width (Figure 8).

For the maxilla, the jugal point (Mx) is located on the right

and left sides of the maxillary skeletal base at “the depth

of the concavity of the lateral maxillary contours, at the

junction of the maxilla and the zygomatic buttress.”3 The

maxillary width is determined by the horizontal distance

connecting these two points. For the mandible, a similar

measurement is taken between the two antegonial notches

(Ag). These notches are located on the right and left sides

of the mandibular body at the “innermost height of contour

along the curved outline of the inferior mandibular border,

Figure 7 Rationale for normalizing the transverse dimension.

Figure 8 Locations of Mx (green) and Ag (yellow).

below and medial to the gonial angle.”3

Once the measurements have been taken, the mandibular

width (Ag-Ag) is subtracted from the maxillary width (Mx-

Mx) to get the difference in width between the jaws. Ricketts

then determined skeletal age-determined normative relation-

ships between the maxilla and the mandible (Figure 9). This

allows the analysis to accommodate growing patients, and

allows for the differential growth rates and potentials of the

maxilla and the mandible.

In order to determine the skeletal age of a patient, a hand-

wrist film is taken and is compared to an atlas of male and

female skeletal age standards.29 To determine the amount of

expansion needed, the age-adjusted expected difference be-

tween the jaws is subtracted from the measured difference.

An example of the Ricketts method is shown in Figure 10.

Andrews’ Element III AnalysisIn 1970, L. F. Andrews published his landmark paper describ-

ing the six keys to normal static occlusion.1 Over the next

several decades, he and his son, W. A. Andrews, worked to de-

velop the six elements philosophy of orthodontic diagnosis.

One of the diagnostic criteria, Element III, is devoted to ana-

lyzing the transverse relationship of the maxilla and mandible

and is based on both bony and dental landmarks.10

The Element III analysis is based on the assumption that

the WALA (named after Will Andrews and Larry Andrews)

Figure 9 Table for determining the age-normal difference between the maxilla and the mandible.

Figure 10 Example of Ricketts’ P-A analysis.


ridge determines the width of the mandible. According to

Andrews’ definition, the WALA ridge is coincident with the

most prominent portion of the buccal alveolar bone when

viewed from the occlusal surface (Figure 11).

The WALA ridge is essentially coincident with the

mucogingival junction and approximates the center of re-

sistance of the mandibular molars. In a mature patient,

the WALA ridge and the width of the mandible cannot be

modified with conventional treatment. Thus the WALA ridge

forms a stable basis for the Element III analysis.6

The Element III analysis is based on the width change,

if any, of the maxilla needed to have upper and lower pos-

terior teeth upright in bone, centered in bone, and properly

intercuspated. To determine the discrepancy, the first step is

to determine the width of the mandible, or the horizontal

distance from the WALA ridge on the right side to the WALA

ridge on the left side. According to Andrews, optimally po-

sitioned mandibular molars will be upright in the alveolus,

and their facial axis (FA) point, or center of the crown, will

be horizontally positioned 2 mm from the WALA ridge. With

this information, the width of the mandible is then defined as

the WALA-WALA distance minus 4 mm.6

Figure 11 Demarcation of the WALA ridge.

The width of the maxilla is based on optimization of the

angulation of the maxillary molars. To determine this width,

one measures the horizontal distance from the FA point of

the left molar to the FA point of the right molar and records

the measurement.

One then looks at the angulation of the maxillary mo-

lars and estimates the amount of horizontal change that will

occur between the FA points of the right and left molars

when they are optimally angulated. The estimated amount of

change is subtracted from the original FA-FA measurement.

The result represents the width of the maxilla.6

In order to have optimally positioned and optimally in-

clined molar teeth that intercuspate well, Andrews states that

the maxillary width must be 5 mm greater than the mandib-

ular width.6 In order to determine the amount of transverse

discrepancy, or Element III change, needed to produce an

ideal result, one takes the optimal mandibular width, adds

5 mm, and subtracts the maxillary width. An example of the

entire analysis is shown in Figure 14.

Figure 13 Determining maxillary FA-FA distance and estimating the change in maxillary molar inclination.

Figure 12 Determination of mandibular WALA-WALA and FA-FA distances.

Figure 14 Example of Andrews’ Element III transverse analysis.

16

University of Pennsylvania Cone-Beam CT AnalysisThe current trend in orthodontic imaging and diagnosis is

toward three-dimensional analysis. With the advent of cone-

beam imaging, orthodontists can obtain precise measure-

ments without any distortion caused by radiographic projec-

tions or ambiguity of point identification. The same rationale

can subsequently be applied to the transverse measurement

of the maxilla and the mandible. Ricketts’ and Andrews’

methods for determining the amount of transverse discrep-

ancy between the jaws are based on using readily discernable

landmarks that represent the width of the base of the alveo-

lar housing. For Ricketts, these landmarks are Mx-Mx for

the maxilla and Ag-Ag for the mandible. For Andrews, these

landmarks are the two sides of the WALA ridge and the FA

points of the maxillary and mandibular molars. The WALA-

WALA measurement represents the width of the mandible,

and the FA-FA points are used, as described above, to deter-

mine the width of the maxilla. Both of these methods have

merit. However, with cone-beam CT imaging, it is no lon-

ger necessary to have a measurement dictated by ease with

which landmarks can be identified to represent the widths

of the jaws.

Before choosing a method for measuring the base of the

jaws, we must first decide what location to use for measure-

ment. In determining the location of the WALA ridge, An-

drews stated that the WALA ridge is an approximation of the

center of resistance of the mandibular teeth. Above the WALA

ridge, the alveolus can be dimensionally molded and altered,

depending on the change in angulation of the teeth. However,

the same cannot be said for the portion of the alveolus below

the WALA ridge. Thus, in a mature patient, any portion of the

alveolus apical to the WALA ridge can be assumed to be rea-

sonably dimensionally stable during tooth movement, and,

therefore, can define the dimensions of the patient’s arch. In

Ricketts’ analysis, Ag-Ag represents the basal portion of the

mandible. However, when one looks at the position of Ag on

a three-dimensional image, one sees that its correlation with

the base of the alveolus is relatively weak in all three planes

of space for mature patients (Figure 15).

Tamburrino et al | The Transverse Dimension: Diagnosis and Relevance to Functional Occlusion

Thus, to locate the beginning of the base of the mandible

with a CT scan, it would seem best to find the skeletal represen-

tation of the WALA ridge. This is approximately at the edge of

the cortical bone opposite the furcation of the mandibular first

molars. We can also use this technique to locate the beginning of

the base of the maxilla. If we assume that the maxilla begins at

the projection of the center of resistance of the maxillary teeth

onto the buccal surface of the cortical bone, Ricketts’ use of Mx

to determine maxillary width appears to be at approximately at

the same horizontal position. Additionally, by using Mx point,

any exostoses present along the buccal portion of the alveo-

lus will not interfere with the measurement. Andrews’ method,

on the other hand, has no directly definable skeletal landmark

for the maxilla; it relies on estimated changes in the angulation

of the molars to determine the skeletal transverse discrepancy.

Therefore, Ricketts’ method of defining the basal skeletal width

of the maxilla appears to be more appropriate.

We begin, then, by defining locations for measuring max-

illary and mandibular skeletal basal width. Next, we explore

concepts for defining these locations on cone-beam CT imaging.

The basic premise for the mandible is to locate the most buccal

point on the cortical plate opposite the mandibular first molars

at the level of the center of resistance. According to Katona, this

location is approximately coincident with the furcation of the

roots of the molars.30 As we explained above, the authors chose

this point due to the relative immutability of the alveolus apical

to this location with orthodontics and because it represents the

absolute minimal width of the basal bone for each jaw.

For the purposes of this technique, the authors used Dol-

phin 3D, release 11 (Patterson Dental, Chatsworth, CA), but

the concepts can be applied to any software with the capabil-

ity to analyze a cone-beam CT image. After properly orienting

the image, we open the multiplanar view (MPV) screen to see

simultaneous axial, sagittal, and coronal cuts of the image.

Figure 15 Correlations of Mx and Ag to skeletal bases in adults.


To determine the width of the mandible, we scroll down

through the image until we locate the furcation of the first

molar. Then we scroll posteriorly through the scan until we

locate the coronal cross-section through the center of the

mandibular first molars.

Now we switch to full-screen axial view. Using the cut

lines as a guide, we measure the width of the mandible from

the intersection of the cut line with the most buccal portion

of the cortical plate on both the right and left sides.

Figure 16 MPV of a cone-beam CT scan.

Figure 17 Location of the mandibular axial and coronal cuts.

For the maxilla, a similar method is employed. The only

difference is that the axial and coronal cuts must be taken at

the position Mx-Mx, and the same measurement as in the

Ricketts’ analysis is used.

The analysis of the width of the maxilla and mandible at

the level of the first molars is straightforward once we have

Figure 18 Measurement of mandibular skeletal width.

Figure 19 Measurement of maxillary axial and coronal cuts.

Figure 20 Measurement of maxillary skeletal width.


taken the measurements of both jaws. By subtracting the

mandibular width from the maxillary width, we determine

the difference between the two jaws. Both Ricketts’ and An-

drews’ analyses demonstrate that the optimal transverse dif-

ference between the maxilla and mandible is 5 mm in mature

patients. A preliminary analysis of 5 cases where the maxil-

lary and mandibular molars were upright in the alveolus,

centered in the alveolus, and well intercuspated, produced

measurements where the difference between the width of the

jaws approximated 5 mm on a consistent basis. Therefore,

the seemingly ideal difference for the width of the jaws in

mature patients using the Penn CBCT analysis would also

appear to be 5 mm. To determine the amount of expansion

necessary to achieve an ideal jaw relationship in the trans-

verse dimension, the measured difference between the jaws

should be subtracted from 5.

Research performed by Simontacchi-Gbologah, et al31,

has verified the validity of the University of Pennsylvania

CBCT analysis for the transverse diagnosis. However, the

difference between the described method here and the meth-

od in the aforementioned research is that the measurements

were taken on coronal cuts, not axial ones. Due to the cross

section of the mandibular coronal cut being taken at an angle

Figure 21 Example of optimal transverse skeletal relationships using cone-beam CT analysis.

that is not perpendicular to the alveolus, a false perception of

the thickness of cortical bone is possible, as shown in Figure

22. Therefore, to reduce errors in judgment and to improve

visualization of the most buccal portion of the cortical bone,

the authors believe that the axial cut allows for greater preci-

sion of measurement over the coronal cross section.

Future DirectionsNow that the methodology of the Penn CBCT analysis has

been verified, the next goal will be to extrapolate the analysis

to determine a diagnostic transverse relationship for the ca-

nines. With this, the goal will be to determine the appropriate

arch form for proper stability and function on an individual

basis. An additional study’s aim will be to develop age-spe-

cific transverse normative criteria for Penn CBCT analysis,

similar to Ricketts’ norms for the P-A ceph. ■

References 1. Andrews LF. The six keys to normal occlusion. Am J Orthod. 1972; 62(3):296-309.

2. Jarabak cephalometric analysis. In: Roth-Williams/AEO Course Manual; 2006.

3. Ricketts RM. Introducing Computerized Cephalometrics. Rocky Mountain Data Systems; 1969.

4. Steiner CC. The use of cephalometrics as an aid to planning and as-sessing orthodontic treatment. Am J Orthod. 1960; (29):8.

5. Downs WB. Analysis of the dentofacial profile. Angle Orthod. 1956; (26):191.

6. Andrews LF, Andrews WA. Andrews analysis. In: Syllabus of the An-drews Orthodontic Philosophy. 9th ed. Six Elements Course Manual; 2001.

7. McNamara JA, Brudon WL. Orthodontics and Dentofacial Ortho-pedics. 2nd ed. Ann Arbor, MI: Needham Press; 2002: 102-103.

Figure 22 Visualization of cortical bone thickness on coronal and axial cuts of the same patient


8. Vanarsdall RL. Transverse dimension and long-term stability. Sem in Orthod. 1999; 5(3):171-180.

9. Cordray FE. Three-dimensional analysis of models articulated in the seated condylar position from a deprogrammed asymptomatic popula-tion: a prospective study, I. Am J Orthod Dentofac Orthop. 2006; (129): 619-630.

10. Utt TW, Meyers CE, Wierzbe TF, Hondrum SO. A three-dimension-al comparison of condylar position changes between centric relation and centric occlusion using the mandibular position indicator. Am J Orthod Dentofac Orthop. 1995; (107): 298-308.

11. Crawford SD. The relationship between condylar axis position as determined by the occlusion and measured by the CPI instrument and signs and symptoms of TM joint dysfunction. Angle Orthod. 1999;(69): 103-115.

12. Tamburrino RK, Secchi AG, Katz SH, Pinto AA. Assessment of the three-dimensional condylar and dental positional relationships in CR-to-MIC shifts. RWISO Journal 2009; 1(1): 33-42.

13. McNamara JA, Brudon WL. Orthodontics and Dentofacial Ortho-pedics. 2nd ed. Ann Arbor, MI: Needham Press; 2002: 104-105.

14. McMurphy JS, Secchi AG. Effect of Skeletal Transverse Discrep-ancies on Functional Position of the Mandible [thesis]. University of Pennsylvania; 2007.

15. Greco PM, Vanarsdall RL, Levrini M, Read R. An evaluation of anterior temporal and masseter muscle activity in appliance therapy. Angle Orthod. 1999; 69(2): 141-141.

16. Williamson EH, Lundquist DO. Anterior guidance: its effect on electromyographic activity of the temporal and masseter muscles. J. Prosthet Dent. 1983; (69): 816-823.

17. Manns A, Chan C, Miralles R. Influence of group function and canine guidance on electromyographic activity of elevator muscles. J Prosthet Dent. 1987; (57): 494-501.

18. Okano N, Baba K, Igarashi Y. Influences of altered occlusal guid-ance on masticatory muscle activity during clenching. J Oral Rehab. 2007; (9): 679-684.

19. Herberger T, Vanarsdall RL. Rapid Palatal Expansion: Long-Term Stability and Periodontal Implications [thesis]. University of Pennsyl-vania; 1987.

20. Sarver DM, Proffit WR. In: Graber TM, Vig KL, Vanarsdall RL, eds. Orthodontics: Current Principles and Techniques. 4th ed. St. Louis, MO: Elsevier-Mosby; 2005: 15.

21. Harrell SK. Occlusal forces as a risk factor for periodontal disease. Periodon. 2003; (32): 111-117.

22. Nunn ME, Harrell SK. The effect of occlusal discrepancies on periodontitis: relationship of initial occlusal discrepancies to initial clinical parameters. J Periodontol. 2001; (72): 485-494.

23. Nunn ME, Harrell SK. The effect of occlusal discrepancies on periodontitis: relationship of occlusal treatment to the progression of periodontal disease. J Periodontol. 2001; (72): 495-505.

24. Ricketts RM. Respiratory obstruction syndrome. Am J Orthod. 1968;(54):495-507.

25. Comyn FL. MRI Comparison of Craniofacial Structures in Sleep Apneic Patients [master’s thesis]. University of Pennsylvania; 2009.

26. Cappetta LS, Chung CH, Boucher NS. Effects of Bonded Rapid Palatal Expansion on Nasal Cavity and Pharyngeal Airway Volume: A Study of Cone-Beam CT Images [thesis]. University of Pennsylvania; 2009.

27. Kilic N, Oktay H. Effects of rapid maxillary expansion on nasal breathing and some naso-respiratory and breathing problems in grow-ing children: a literature review. Int J Pediatr Otorhinolaryngol. 2008; 72(11): 1595-1601.

28. Oliveira de Felippe NL, Da Silveira AC, Viana G, Kusnoto B, Smith B, Evans CA. Relationship between rapid maxillary expansion and nasal cavity size and airway resistance: short- and long-term effects. Am J Orthod Dentofac Orthop. 2008; 134(93): 370-382.

29. Greulich WW, Pyle SI. Radiographic Atlas of Skeletal Development of the Hand and Wrist. 2nd ed. Stanford, CA: Stanford University Press; 1959.

30. Katona TR. An engineering analysis of dental occlusion principles. Am J Orthod Dentofac Orthop. 2009; 135(6): 696.

31. Simontacchi-Gbologah MS, Tamburrino RK, Boucher NS, Va-narsdall RL, Secchi AG. Comparison of Three Methods to Analyze the Skeletal Transverse Dimension in Orthodontic Diagnosis [thesis]. University of Pennsylvania; 2010.

For complete contributor information, please see next page.


ContributorsRyan K. Tamburrino, DMD■ Clinical Associate—Univ. of Penn., School of Dental Medicine, Dept. of Orthodontics■ Andrews Foundation “Six Elements Philosophy” Course—2007 ■ Advanced Education in Orthodontics—Roth-Williams Center for Functional Occlusion—2008■ University of Pennsylvania, School of Dental Medicine, Certificate in Orthodontics—2008■ University of Pennsylvania, School of Dental Medicine, DMD —2006

Normand S. Boucher, DDS■ McGill University, School of Dental Medicine, DMD, 1974■ University of Pennsylvania, School of Dental Medicine, Certificates in Orthodontics and Periodontics, 1982■ Advanced Education in Orthodontics, Roth-Williams Center for Functional Occlusion, 1993■ Andrews Foundation, “Six Elements Philosophy” Course, 1998■ Clinical Associate Professor, University of Pennsylvania, School of Dental Medicine, Department of Orthodontics

Robert L. Vanarsdall, DDS■ Professor and Chair— University of Pennsylvania School of Dental Medicine, Department of Orthodontics■ DDS—Medical College of Virginia■ Certificates in Orthodontics and Periodontics—University of Pennsylvania■ 80 publications and 11 textbook contributions■ Former President of the Philadelphia Society of Orthodontists and Eastern Component of the EH Angle Society

Antonino G. Secchi, DMD, MS■ Assistant Professor of Orthodontics-Clinician Educator and Clinical Director, Dept. of Orthodontics, University of Penn.■ Andrews Foundation “Six Elements Philosophy” Course, USA, —2005■ Institute for Comprehensive Oral Diagnosis and Rehabilitation, OBI Level III—2005■ Advanced Education in Orthodontics—Roth/Williams Center for Functional Occlusion USA—2005■ University of Pennsylvania, MS in Oral Biology—2005■ University of Pennsylvania, DMD—2005■ University of Pennsylvania, Certificate in Orthodontics—2003■ University of Chile—Chile, Certificate in Occlusion, 1998■ University of Valparaiso—Chile, DDS, 1996


Summary

The Axi-Path SystemMany clinicians use the Panadent Axi-Path system for the

following purposes: (Figure 17)

To locate the true hinge axis (THA)•

To determine the sagittal anterior condylar path in-•

clination, non-working-side sagittal lateral condy-

lar path inclination, and the Bennett movement to

select the Motion Analog Blocks

To assess the functional structural conditions of the •

temporomandibular joint

The upper head frame of the Axi-Path recorder is com-

posed of two symmetrical arms that move around a hinge

joint at the center of the frame (Figure 18). The upper frame

is fitted and fastened to the head by tightening the hinge with

a thumbscrew. A straight ruler can be used to make the two

flag tables parallel to each other. (Figure 19).

This is the second part of a two-part paper discussing the need for accuracy

in the mounting of dental models for orthodontic diagnosis and treatment.

Part 1 discussed the accuracy differences between an arbitrary hinge axis

(AHA) mounting and a true hinge axis (THA) mounting. Part 2 discusses the

differences between two popular true hinge axis recording devices, the Pana-

dent Axi-Path system and the Axiograph III system.

Byungtaek Choi, DDS, MS, PhD

byunGTaeK choi, ddS, mS, [email protected]■ Graduated from Seoul National University, College of Dentistry (DDS), Seoul, Korea, 1981■ Graduated from Seoul National University, College of Dentistry (MS), Seoul, Korea, 1984■ Graduated from Seoul National University, College of Dentistry (PhD), Seoul, Korea, 1990■ Private Practice, Seoul, Korea ■ Chairman of Korean Foundation of Gnatho-Orthodontic Research■ Director of Roth Williams Center, Korea■ Attending Professor of Medical School of Hanlim University■ Attending Professor at Seoul National University

Hinge Axis: The Need for Accuracy in Precision MountingPart 2

Figure 17 Axi-Path recording: Panadent Company.

Figure 18 Head frame (upper frame).

22 Choi | Hinge Axis: The Need for Accuracy in Precision Mounting Part 2

The lower head frame of the Axi-Path recorder is at-

tached to the lower jaw with the use of a clutch. Two side

arms which hold the styli are attached to the cross rod to

record the mandibular movement (Figure 20).

To place the Axi-Path recorder correctly, the upper

frame is first fitted and fastened to the head. The lower frame

is then attached to the lower jaw. Finally, the axis-locating

arms are attached to the lower jaw (Figure 21).

Figure 22 is the schematic drawing of the head viewed

from the top when the Axi-Path recorder has been placed on

the head correctly.

Figure 19 Flag tables are set to be parallel to each other.

Figure 20 Lower frame for adjustable axis-locating arms.

Figure 21-a The upper frame is placed and fastened to the head. Figure 21-b Axis-locating arms are attached to the lower jaw.

Figure 22 Schematic drawing of the head viewed from the top when the Axi-Path recorder has been placed on the head.

If the patient’s head configuration is asymmetrical, the

face-bow may not be centered on the head when the nasion

relator is placed on Nasion (Figure 23). Since the nasion rela-

tor cannot move transversely, the face-bow should be rotated

until the nasion relator sits on Nasion (Figure 24). When the

lower frame is placed, the stylus may not be perpendicular

Figure 23 Asymmetrical head configuration.


The following experiment can be used to determine the

magnitude of measurement error. The experiment is set up so

that the measurement shows the right condyle 5 mm forward

of its actual position. For purposes of illustration, the situa-

tion is assumed to be noncollinear (Figure 26).

The new hinge axis diverges from the original hinge axis

as it goes farther from the anatomic structure (Figure 27).

The right recording stylus is placed at the new hinge

point on the flag table (Figure 28).

to the flag table (Figure 25). The Axi-Path is not a collinear

system, and errors often occur when the clinician attempts

to determine the THA. If a recording system is not collinear

and rectilinear, the clinician is likely to mark the inaccurate

hinge points on the skin.

Figure 24 Nasion relator cannot move along the horizontal part of the bow.

Figure 25 When the lower frame is placed, the stylus may not be perpendicular to the flag table.

Figure 26 Supposition. Right condyle moved 5 mm forward.

Figure 27 New hinge axis passing through newly positioned condyle.


A hinge axis is not a line that connects the centers of the

condyles. It is the axis around which the mandible shows

pure hinge movement. Therefore, the hinge axis may pass

through any point in the condyle. In Figure 29, the center

points have been marked for clarity. Figure 30 is a magnified

view of the right joint area.

Figure 28 Stylus placed at the new hinge point on the flag table.

Figure 29

Figure 30 Magnified view of the right joint area.

Right condyle 5 mm anterior to the left condyle.

The example assumes that the distance between the

centers of the two condyles is 110 mm, and the distance at

skin level is 140 mm (Figure 31). If the condyle moves 5 mm

forward, it will appear to move slightly more on the graph

(Figure 32). If the condyle moves 5 mm forward, the hinge

point on the skin moves 5.68 mm forward (Figure 33).

Figure 31 The supposition is that the distance between the centers of the two condyles is 110 mm,

and the distance at the skin level is 140 mm.

Figure 32 If the condyle moves 5 mm forward, it will appear to move slightly more on the graph.

Figure 33 If the condyle moves 5 mm forward, the hinge point on the skin moves 5.68 mm forward.


The Axi-Path is designed so that the flag table is very

close to the preauricular skin. For some patients, depending

on the configuration of the temporal region, the flag table

may be farther from the skin. Figure 34 shows 5 mm of dis-

tance between the skin and the flag table.

If the distance from where the stylus contacts the flag

table to the skin is 5 mm, the measurement error will be 0.23

mm. The amount of error will decrease as the stylus gets

closer to the skin. The Axi-Path system uses the skin mark

for face-bow transfer. Hence, the smaller the error, the more

accurate the hinge axis. Accuracy depends on the distance

between the flag table and the skin (Figure 35).

The Axi-Path system has some advantages. Because the

flag table is very close to the skin, measurement error can be

minimized (Figure 36). And the reference tattoo on the skin

can be used for precision mounting at any time, once it has

been marked (Figure37).

Figure 34 Axi-Path is designed so that the flag table is very close to the preauricular skin. This picture shows 5 mm of distance between the skin and the flag table.

Figure 35 If the distance from the stylus to the skin is 5 mm, the amount of error is calculated as follows:

5.68 : 125 = X : 5 mm (X = 284 ÷ 125 = 0.23 mm)

However, the Axi-Path system also has shortcomings.

The head frame often cannot be fastened tightly to the head.

It is somewhat unstable compared to the frame of the Ax-

iograph III. An unstable frame can make it difficult or im-

possible to get a reproducible reference point and may be

misdiagnosed as an unstable joint (Figure 38).

Figure 36 Advantages of Axi-Path system: Proximity of the flag table to the skin.

Figure 37 Advantages of Axi-Path system: Proximity of the flag table to the skin.

Figure 38 Shortcomings of Axi-Path system: Unstable head frame.


The Axiograph III SystemThe Axiograph III system is shown in Figure 41. Orthodon-

tists use this system for the same purposes as the Axi-Path

system. The Axiograph III system differs from the Axi-Path

system in several important ways.

Figure 42 is a schematic drawing of the head viewed

from the top when the upper frame of the Axiograph III has

been placed on the head correctly. If the patient’s head is

symmetrical, every part of the frame will be parallel or per-

pendicular to the sagittal plane of the head.

This system is collinear and rectilinear. Since the nasion

relator moves transversely, the upper frame can be placed

on the head without losing the parallelism, even when the

patient’s head is asymmetrical (Figure 43).

Figure 44 shows the upper and lower frames placed on

the head. The lower frame has two side arms, with a stylus

on the end of each arm. The two styli are in collinear align-

ment, rectilinear with the upper Axiomatic flag-bow record-

ing plates (Figure 45).

Since the nasion relator is not movable transversely on

the face-bow, it is difficult to center the midline of the bow

perpendicular to the hinge axis in asymmetrical cases. If we

attempt to do so, the face-bow will be seated off center (Fig-

ure 39).

In short, the Axi-Path system records the hinge axis on a

flag table that is relatively close to the skin. If the flag table is

close to the skin, it produces a more accurate hinge mark on

the skin. However, the primary disadvantages of this system

are the structural instability of the head frame when fastened

to the head and the off-centered seating of the face-bow on

the asymmetrical head.

Figure 39 Shortcomings of Axi-Path system: Off-center placement of the upper frame in asymmetrical cases.

Figure 41 Axiograph III: SAM.

Figure 42 Schematic drawing and real picture of upper frame.


Figure 43 Nasion relator moves transversely along the horizontal part of frame so the frame can be placed on the head without losing parallelism.

Figure 44 Upper and lower frames that have been placed on the head.

Figure 45 Axiograph III uses two recording styli in a collinear alignment, rectilinear with the upper

Axiomatic flag-bow recording plates.

The upper frame is fastened to the head first, and the

lower frame is placed next. If earplugs are inserted into the

auditory canals, the alignment pins automatically indicate

the approximate hinge positions. The alignment pins also

make the upper and lower parts of the face-bow parallel and

perpendicular to each other (Figure 46).

As was done in the Axi-Path experiment, the amount of

measurement error is then determined when the right con-

dyle is moved 5 mm forward (Figure 47). This movement

produces a new hinge axis, which in turn makes new hinge

points on the skin. The new hinge axis diverges from the

original hinge axis as it moves farther from the anatomic

structure (Figure 48).

Figure 46 If ear plugs are inserted into auditory canals, alignment pins automatically indicate approximate hinge

positions. The alignment pins also make the upper and lower parts of the face-bow parallel and perpendicular to each other.

Figure 47 Supposition: Right condyle moved 5 mm forward.


Figure 48 New hinge axis passing through newly positioned condyle.

Figure 49 is a magnified view of the right joint area.

The example assumes that the distance between the cen-

ters of the two condyles is 110 mm, and that the distance at

skin level is 140 mm. If the condyle moves 5 mm forward, it

will appear to move slightly more on the graph (Figure 50).

The recording stylus will point to the new hinge on the

flag table (Figure 51).

If the condyle moves 5 mm forward, the hinge point on

the skin will move 5.68 mm forward (Figure 52).

Figure 49 The supposition is that the distance between the centers of the two condyles is 110 mm, and the

distance at the skin level is 140 mm.

Right condyle 5 mm anterior to the left condyle.

Figure 50 If the condyle moves 5 mm forward, it will appear to move slightly more on the graph.

Figure 51 The recording styli will point to the new hinge on the flag table.

Figure 52 IIf the condyle moves 5 mm forward, the hinge point on the skin will move 5.68 forward. The distance between the skin and the graph table is usually greater in Axiograph III than in Axi-Path. Taking this into account, the distance between the

skin and the graph was set at 8 mm in Axiograph III, instead of 5 mm, as in Axi-Path.


Although this situation is one that we may not encoun-

ter in practice, it is useful as an example to explain an ex-

treme case (Figure 55).

It is obvious that the measurement error becomes larger

when the distance from the stylus to the skin is 50 mm (Figure

56). In fact, the measurement error will be 2.3 mm (Figure 57).

The distance between the preauricular skin and the flag

table is usually greater in the Axiograph III than it is in the

Axi-Path. Taking this into account, the distance between the

skin and the flag table was set at 8 mm in the Axiograph III.

When the flag table is 8 mm away from the skin, the mea-

surement error will be 0.36 mm. This is 0.13 mm larger than

the 0.23 mm measurement error with the Axi-Path, which

has the flag table 5 mm away from the skin (Figure 53).

If we were to transfer the face-bow of the Axiograph III

system in the same way as we transfer the face-bow of the

Axi-Path system, we would have to shorten the distance be-

tween the skin and the flag table to reduce the measurement

error. However, in the Axiograph III system we use hinge

marks on the graph, rather than hinge marks on the skin, for

precision mounting.

Now let us further suppose that the stylus is placed 50

mm, rather than 8 mm, away from the skin (Figure 54).

Figure 53 If the distance from the stylus to the skin is 8 mm, the amount of error will be calculated as follows:

5.68 : 125 = X : 8 mm (X = 45.4 ÷ 125 = 0.36 mm)

Figure 54 Supposition: The stylus is 50 mm away from the skin.

Figure 55 Magnified view.

Figure 56 The measurement error becomes larger when the distance from the stylus to the skin

changes from 8 mm to 50 mm.

Figure 57 If the distance from the stylus to the skin is 50 mm, the amount of error will be calculated as follows:

5.6 8: 125 = X : 50 mm (X = 284 ÷ 125 = 2.3 mm)


This is an extremely large error when we are attempting

to locate a THA. Fortunately, it seldom happens that we at-

tempt to locate a THA from a distance of 50 mm in clinical

practice (Figure 58).

The fact remains, however, that the greater the distance

between the skin and the stylus, the less accurate are the

marks on the skin (Figure 59). Therefore, we are likely to

make a large error if we use a false hinge axis that deviates

substantially from the THA (Figure 60).

Figure 58 If we try to extend the stylus to the skin to mark a hinge point from a point located at a far distance from the skin using Axiograph III, it would result in a very large error.

Figure 59 The greater the distance between the skin and the stylus, the less accurate the marks of

the THA on the skin will be.

Figure 60 We are likely to create a large error if we use the false hinge axis, which deviates substantially from the THA.

Precision mounting using a false hinge axis results in a very large error.

Next, let us examine the precision mounting system of

the Axiograph III. Figure 61 shows a magnified view of the

highlighted area. The various parts of the highlighted area

are shown in Figure 62. They are, respectively, the side arm

of the upper frame, the flag table attached to the side arm,

the recording arm of the lower frame, and the stylus attached

to the recording arm.

The THA is the line that connects the left and the right

styli. It passes through an imaginary hole in the flag table.

The stylus marks the hinge point in red or blue on the graph

of the flag table (Figures 63 and 64).

Figure 61 Schematic drawing and real picture of the stylus area.

Figure 62 Magnified view


Figure 63 Flag table.

Figure 64 Flag table.

The hinge point on the graph is isolated with the hinge

axis clamp. The hinge axis clamp has two bars. Each bar has

a hole in it, and the two holes are aligned (Figures 65 and

66).

Figure 65 Flag table with hinge axis clamp.

Figure 66 Schematic drawing and real picture of the flag table and the clamp.

The precision mounting stand has two hinge axis align-

ment pins. These pins are designed to fit into the small holes

on the inner bar of the hinge axis clamp (Figures 67-a, b).

Figure 67-a Hinge axis alignment pin fits into the inner clamp hole.

Figure 67-b Hinge axis alignment belongs to mounting stand.


In this respect, the Axiograph III system differs from

the Axi-Path system; in the Axi-Path, the stylus of the lower

frame fits into the female part of the mounting shaft. There-

fore, we do not need to re-mark the hinge point on the skin

with the Axiograph III as we do with the Axi-Path. Instead,

we use the hinge points on the graphs for precision mount-

ing. In other words, we treat the graph as if it were the skin

in the Axiograph III system (Figure 68).

The distance from the tip of the hinge axis alignment

pin to the THA is the measurement error (Figure 69). It is in-

teresting to observe that the measurement error increases as

the flag table moves closer to the skin medially (Figure 70).

Conversely, the measurement error decreases as the flag table

moves farther from the skin laterally (Figure 71).

Figure 68 In Axi-Path, the stylus (axis pin) of the lower frame is adapted to the female part of the mounting shaft. In

Axiograph III, the hinge axis alignment pins of the mounting stand are fitted into the small holes on the inner bar of the hinge axis clamp. Therefore, we need not re-mark the hinge

point on the skin, as we do with Axi-Path. Instead, we use the hinge points on the graphs for precision mounting.

Figure 69 The distance from the tip of the hinge axis alignment pin to the THA is the measurement error.

Figure 70 Measurement error increases as the flag table moves closer to the skin medially.

Figure 71 Measurement error decreases as the flag table moves farther from the skin laterally.

If we try to extend the hinge axis-locating stylus from

the flag to the skin to mark an axis as we do in the Axi-Path

system, the new hinge point on the skin will not correspond

to the true hinge point. As a result, the precision mounting

will be inaccurate. In the Axiograph III system, the measure-

ment error decreases as the flag table gets farther away from

the skin and the constructed hinge axis gets closer to the

THA (Figure 72).

Now let us consider two situations that we may encoun-

ter in clinical practice. In the first situation, the side arm of

the upper frame contacts the skin of supraauricular area

(Figure 73). The side arm is 6 mm wide and the flag table is

4.5 mm thick.

In the second situation, there may be some distance be-

tween the condyle and the recording flag, depending on the

configuration of the patient’s head. For the purposes of illus-

tration, we will assume that the side arm is 3 mm away from


Figure 72

the skin. In fact, this does not actually happen in clinical

practice, because we always push the side arm onto the skin

to fasten the upper frame to the head. If, however, we assume

3 mm of separation, this means that the flag table will be 6.5

mm away from the skin, and the hinge point locator clamp

will be attached to the flag table (Figure 74).

Figure 73 Supposition: The side arm contacts the skin.

Figure 74 Supposition: The side arm is separated 3 mm from the skin. The hinge point is measured

at level of entrance of the clamp hole.

In this example (Figure 74) the thickness of the hinge

axis clamp is 5.75 mm; the distance from the skin to the

inner surface of the flag table is 6.5 mm; the distance from

the skin to the outer surface of the flag table is 11 mm; the

distance from the left condyle to the skin on the right side of

is 110 + 15 mm; and the distance from the left condyle to the

inner surface of the flag table is 110 + 15 + 6.5 mm. This is

indicated by the yellow arrow.

The measurement error at the position indicated by the

arrow is calculated as follows:

Y is the measurement error on the inner surface of the •

flag table. The amount of error is 0.20 mm (Figure 75).

The measurement error at the inner entrance of the •

hinge axis clamp increases slightly (Figure 76).

Figure 75 Y is the measurement error on the inner surface of the flag table. The amount is 0.20 mm.

Figure 76 Supposition: The side arm is separated 3 mm from the skin. The hinge point is measured at

level of entrance of the clamp hole.


The measurement error at the inner entrance is 0.47 •

mm (Figure 77).

The measurement error on the skin increases even •

more (Figure 78).

The measurement error on the skin is 0.5 mm •

(Figure 79).

•

Figure 77 The amount of measurement error will be 0.47 mm.

Figure 78 Supposition: The side arm is separated 3 mm from the skin. The hinge point is measured at

level of entrance of the clamp hole.

The measurement error on the inner surface of the •

flag table is 0.20 mm and this is almost the same as

or smaller than that of Axi-Path.

Although the clamp hole provides a bit of leeway with

the pin fitted, this seems to have no clinical significance. Since

the Axiograph III system uses the hinge point on the graph,

while the Axi-Path system uses the hinge mark on the skin,

the two systems seem to yield almost the same accuracy in

precision mounting (Figure 80).

Summary and ConclusionsThe measurement errors of the hinge axis locations were

calculated for the two recording systems, the Axi-Path of

Panadent and the Axiograph III of SAM. The amount of

the measurement errors were nearly the same for both sys-

tems. While the Axiograph III system locates the hinge axis

using hinge points on the flag table, the Axi-Path system

locates the hinge axis using hinge marks on the skin. Al-

though the distance between the flag table and the skin is

greater in the Axiograph, we found no significant differ-

ence in accuracy between the two systems, as explained

previously. (Figure 83)

Figure 79 The amount of measurement error will be 0.5 mm.

Figure 80 The measurement error on the inner surface of the flag table is 0.20 mm. Error is the same as,

or less than, with Axi-Path.


Since the Axiograph III system does not mark hinge

points on the skin, it may be necessary to relocate the axes

for each mounting. Mechanical stability of the recording de-

vice is very important for precision. The device must remain

firmly seated on the head. In this respect, the Axiograph III

seems to be superior to the Axi-Path (Figure 85). ■

Figure 85 Mechanical stability of the recording device is very important for precision. In this respect Axiograph III seems to be superior to Axi-Path.

Figure 83 The distance between the flag table and the skin is longer in Axiograph III than in Axi-Path. But since Axiograph III uses hinge points on graph paper to locate the hinge axis, it is equally accurate.

Further ReadingBaldauf A, Mack H, Wirth C G. Bestommung der Scharnierachse mit-tels des äußeren Gehörgangs. IOK, 28. JAHRG. 1996.

Broderson S P. Anterior guidance: The key to successful occlusal treat-ment. J Prosthet Dent. 1978;39:396–400.

Cho Y, Hobo S, Takahashi H.Occlusion. Seoul: Kunja; 1996.

Dawson P E. Evaluation, Diagnosis, and Treatment of Occlusal Prob-lems. 2nd ed. St. Louis, Mo: Mosby; 1989.

Glossary of Dental Prosthodontics. Korea: Korean Association of Prosthodontics; 2006.

Hobo S. Twin-tables technique for occlusal rehabilitation. Pt. 1: Mechanism of anterior guidance. J Prosthet Dent. 1991;66:299–303.

Hobo S. Twin-tables technique for occlusal rehabilitation. Pt. 2: Clini-cal procedures. J Prosthet Dent. 1991;66:471–477.

Lee R L. Panadent instruction manual for advanced articulator system. Panadent Corporation, CA, USA, 1988.

Lundeen H C, Gibbs C H. The Function of Teeth. L and G; 2005.

Nagy W W, Smithy T J, Wirth C G. Accuracy of a predetermined trans-verse horizontal mandibular axis point. J Prosthet Dent. 2002;87:387–394.

Okeson J P. Fundamentals of Occlusion and Temporomandibular Disorders. St. Louis, Mo: Mosby; 1985.

continued on next page...

36

Ramfjord S, Ash M M. Occlusion. 3rd ed. Philadelphia: WB Saunders; 1983.

Simpson J W, Hesby R A, Pfeifer D L, Pelleu G B Jr. Arbitrary man-dibular hinge axis locations. J Prosthet Dent. 1984;51:819–822.

Takahashi I. Surgical-orthodontic treatment of a patient with temporo-mandibular disorder stabilized with a gnathologic splint. Am J Orthod Dentofacial Orthop. 2008;133: 909–919.

Theusner J, Plesh O, Curtis D A, Hutton J E. Axiographic tracings of temporomandibular joint movements. J Prosthet Dent. 1993;69:209–215.

Wirth C G. 20 Jahre Axiographie. IOK, 28. JAHRG. 1996.

Choi | Hinge Axis: The Need for Accuracy in Precision Mounting Part 2


Summary

IntroductionOrthodontists and maxillofacial surgeons are well acquaint-

ed with the effects of condylar resorption (Figure 1).

The clinical outcomes of condylar resorption have been de-

scribed at length in the literature.1-6 The causes, however,

have been elusive, hence the common name idiopathic con-

dylar resorption. Over the last several years, the pathophysi-

ology of articular bone erosion secondary to inflammation

has been well studied. A number of cytokines and proteases

are found in joints that show osseous erosions that are not

present in healthy joints, namely TNF-α, IL-1β, IL-6, and

RANKL and matrix metalloproteinases.

Matrix MetalloproteinasesMMPs are of interest because they are directly responsible

for the enzymatic destruction of extracellular matrix in nor-

mal conditions (angiogenesis, morphogenesis, tissue repair)

and in pathological conditions (arthritis, metastasis, cirrho-

sis, endometriosis). MMPs are endopeptidases that are made

in the nucleus as inactive enzymes, or zymogens. The zymo-

gens travel to the cell membrane, where they are incorporat-

ed. The zymogen is then cleaved into the extracellular matrix

as the active enzyme, where it makes cuts into the protein

chains (collagen types I through IV, gelatin, etc). These cuts

cause the proteins to denature, which results in the destruc-

tion of the matrix. The action of the MMP requires the min-

eral zinc—which is an important part of the MMP’s protein

structure; hence the name metalloproteinase (Figure 2).

Mandibular condylar resorption occurs as a result of inflammation and hor-

mone imbalance. The cause of the bone loss at the cellular level is secondary

to the production of matrix metalloproteinases (MMPs). MMPs have been

shown to be present in diseased temporomandibular joints (TMJs). There is

evidence that tetracyclines help control bone erosions in arthritic joints by

inactivating MMPs. This article reviews the pertinent literature in support of

using tetracyclines to prevent mandibular condylar resorption.

michaeL J. GunSon, ddS, [email protected] ■ Graduated from UCLA School of Dentistry, 1997 ■ Graduated from UCLA School of Medicine 2000■ Specialty Certificate in Oral and Maxillofacial Surgery UCLA, 2003

G. WiLLiam aRneTT, ddS, Facd■ Graduated from USC School of Dentistry, 1972■ Specialty Certificate in Oral and Maxillofacial Surgery UCLA, 1975

Michael J. Gunson, DDS, MD ■ G. William Arnett, DDS, FACD

Condylar Resorption, Matrix Metalloproteinases, and Tetracyclines

Figure 1 Tomograms reconstructed from cone-beam CT scan. They show severe condylar resorption in a 19-year-old female

over a 2-year period. Note the progressive osseous destruction.

38 Gunson, Arnett | Condylar Resorption, Matrix Metalloproteinases, and Tetracyclines

In joints, MMPs are produced by monocytes, mac-

rophages, polymorphonuclear neutrophils, synoviocytes, os-

teoblasts, and osteoclasts. MMPs are generally classified by

the kind of matrix they degrade; thus collagenase, gelatinase

and stromelysin (Figure 3).

The extracellular activity of MMPs is regulated in two

ways, by transcription and by extracellular inhibition. The

transcription of MMPs in the nucleus is controlled by multi-

ple pathways. MMP transcription is activated by sheer stress

to the cell, by free radicals, and by the cytokines TNF-α, IL-

1β, Il-6 and RANKL (Figure 4a). Transcription is suppressed

by the cytokine osteoprotegerin and by the the hormones

vitamin D and estradiol (Figure 4b). After transcription, the

pro-MMP is then sent to the cell membrane, where it is incor-

Figure 2 The zymogen pro-MMP is transcribed in the nucleus and then attached to the cell membrane. It is activated when it is cleaved from the membrane. The zinc (Zn) portion binds

to protein and the enzyme cleaves the protein, destroying the extracellular matrix.

Figure 3 A list of the 28 known MMPs. They are generally named after the extracellular protein that they degrade.

porated. Activation of the MMP occurs when the active side

of the MMP is cleaved from the cell and liberated into the ex-

tracellular matrix. Extracellular inhibition comes from pro-

teins called tissue inhibitors of metalloproteinases (TIMPs).

TIMPs bind to active matrix metalloproteinases and inhibit

their activity (Figure 4c). The ratio of MMP:TIMP activity

influences the amount of matrix degradation.7-10

Figure 4-a MMP transcription is activated in the cell nucleus by cytokines (TNF-α, IL-1β, Il-6, and RANKL); by metabolic by-products (free radicals); and by direct sheer stress

to the cell membrane.

Figure 4-b MMP transcription is inhibited by hormones such as vitamin D and estradiol, as well as the bone-protective

cytokine osteoprotegerin.


des. This evidence supports the presence of 6 of the known

28 matrix metalloproteinases (MMP-1, MMP-2, MMP-3,

MMP-8, MMP-9, and MMP-13) in fluid or tissue samples

obtained from diseased human TMJs.13, 16, 17, 19-34 Some cases

of degenerative joint disease also result from an imbalance

between the activities of MMPs and TIMPs, favoring unreg-

ulated degradation of tissue by MMPs. 35, 36

TetracyclinesBecause MMPs are found to be elevated in patients with

TMJ arthritis and are so destructive to articular tissues, find-

ing a way to reduce their activity or their production would

be helpful in treating patients with arthritis and condylar

resorption.

From 1972-1982, at the School of Dental Medicine in

Stony Brook New York, Ramurmathy and Golub discov-

ered that tetracyclines have anti-collagenolytic properties.

In 1998, Golub and colleagues showed that tetracyclines

inhibit bone resorption in two ways—by controlling the ex-

pression and activity of MMPs and by regulating osteoclasts

and their activity.37

Controlling MMPs With TetracyclinesTetracyclines inhibit MMPs by chelating zinc and by regu-

lating MMP gene expression. As noted above, MMPs need

zinc to actively cleave collagen proteins. Tetracyclines bind

divalent ions, such as zinc. By reducing the amount of free

zinc in tissues, tetracyclines reduce the number of MMPs

available.38 In addition, tetracyclines bind to the MMP itself,

which causes a conformational change in the enzyme, inacti-

vating it (Figure 5).39 Tetracyclines have also been shown to

decrease the transcription of MMPs by blocking both pro-

tein kinase C and calmodulin pathways.40, 41

Figure 4-c The extracellular activity of MMPs is controlled by the presence of inhibitory proteins called tissue inhibitors of metalloproteinases, or TIMPs. TIMPs bind directly to the MMPs, causing conformational changes that prevent the

destruction of matrix proteins.

MMPs and ArthritisThe hallmark sign of arthritis is articular bone loss. In the

past, clinicians have differentiated between inflammatory ar-

thritis and osteoarthritis (OA). Recently, however, the cellular

processes that result in bone and cartilage loss in both forms

of arthritis have been shown to be quite similar.11 While in-

flammatory arthritis is promoted by a systemic problem, the

result is an inflammatory cytokine cascade, which ultimately

results in osteoclastic activity and bone loss at the articular

surface. OA is not a systemic problem but a local one, second-

ary to oxidation reactions, free radical production, or sheer

stress—all three of which result from overuse.12, 13 Despite

the localized nature of OA, the cascade of cellular events that

cause articular surface loss is the same as the systemically in-

duced cascade. An increase in TNF-α and IL-1β increases the

number of osteoclasts and their activity. TNF-α, IL-1β, IL-

6, and RANKL all cause increased expression of the MMP

genes. The end result is destruction of cartilage, bone, and

connective tissue in both arthritis models.14-18

MMPs also respond to systemic hormones such as estro-

gen, vitamin D, and parathyroid hormones. We found an as-

sociation between low estrogen levels and low vitamin D lev-

els in patients with severe condylar resorption.3 All of these

hormones and cytokines are intimately involved in osteoclast

differentiation and activation. This makes sense: MMPs are

osteoclast produced and are responsible for bone and carti-

lage destruction.

MMPs and the TMJThere is substantial evidence indicating that MMPs play an

important role in bone and cartilage degradation associated

with degenerative temporomandibular joint (TMJ) arthriti-

Figure 5 Tetracycline binds directly to the zinc of the MMP. This deactivates the enzyme and protects the matrix

from degradation. Tetracycline also controls osteoclastic activity and MMP transcription.


Regulating Osteoclasts With TetracyclinesOsteoclasts are responsible for the breakdown of bone and

cartilage. Their activity is tightly controlled by cytokines

such as IL-6, TNF-α, nitric oxide, and IL-1β. Tetracyclines

have been shown to prevent the liberation of these cytokines,

diminishing the activity of osteoclasts.42-46 Tetracyclines also

prevent the differentiation of osteoclast precursor cells into

osteoclasts.47 Finally, tetracyclines promote the programmed

cell death (apoptosis) of osteoclasts.48, 49 All these actions re-

sult in a decrease of bone and cartilage loss secondary to

osteoclast activity when tetracyclines are present.

Tetracyclines and ArthritisIn short, the literature shows that tetracyclines exert control

over MMP transcription and activity and regulate osteoclast

activity as well. The clinical evidence supporting the use of

tetracyclines to protect articular bone and cartilage from ar-

thritic inflammation is encouraging.

In the animal model of arthritis, tetracyclines have been

shown to inhibit MMPs and to prevent the progression of

osseous disease.50-52 Yu et al52 induced knee arthritis in dogs

by severing the anterior cruciate ligament. Half the dogs

were pretreated with doxycycline. Doxycycline prevented

the full-thickness cartilage ulcerations that were seen in the

untreated group.

In human studies, tetracyclines have been successfully

used to diminish bone erosions in patients with inflammato-

ry arthritis. One meta-analysis of 10 clinical trials that used

tetracycline for rheumatoid arthritis (RA) showed significant

improvement in disease activity with no side effects.53 In a

single-blinded controlled study, doxycycline was shown to

be as effective as methotrexate in treating inflammatory ar-

thritis.54

Israel et al reported that doxycycline administered at a

dose of 50 mg twice daily for 3 months significantly sup-

pressed MMP activity in three patients diagnosed with ad-

vanced osteoarthritis of the TMJ. Two of the three patients

reported marked improvement in symptoms, including im-

proved mandibular range of motion. One patient did not

experience symptomatic relief despite a marked reduction in

MMP activity.55 While symptomatic relief would be impor-

tant, it must be noted that inhibition of MMPs has a direct

effect on bony resorption, which is often unrelated to TMJ

symptoms. Clinicians need to keep this in mind when re-

viewing the literature.

DosingAt present, there are no definitive studies demonstrating the

efficacy of tetracycline therapy for degenerative TMJ ar-

thritides. However, based on the available information, tet-

racyclines may be considered for the treatment of rapidly

progressive condylar resorption, and in patients with degen-

erative TMJ disease. They may also be used in patients at in-

creased risk for resorption. This includes patients with brux-

ism, inflammatory arthritis, or a past history of resorption

who are undergoing occlusal treatment. Of all the available

tetracyclines, Golub et al found that doxycycline was the

most effective at suppressing MMP activity.56 Appropriate

studies to determine effective dose schedules have not been

conducted to date. However, based on the limited clinical

data, it is reasonable to consider doxycycline at a dose of 50

mg twice daily.

Side EffectsThe adverse effects of tetracyclines are well known. They

include allergic reactions; gastrointestinal symptoms (ulcers,

nausea, vomiting, diarrhea, Candida superinfection); photo-

sensitivity; vestibular toxicity with vertigo and tinnitus; de-

creased bone growth in children; and discoloration of teeth

if administered during tooth development. Tetracyclines may

also reduce the effectiveness of oral contraceptives, potenti-

ate lithium toxicity, increase digoxin availability and toxic-

ity, and decrease prothrombin activity.57

If tetracycline therapy is initiated, the patient should be

advised of the potential for reduced efficacy of oral contra-

ception. In addition, the patient should be cautioned against

sun exposure, and should be monitored for other side effects.

If surgery is contemplated, the patient’s coagulation status

should be evaluated.

There is some question as to whether bacterial resis-

tance may develop with the chronic use of antibiotics. Stud-

ies show that long-term low-dose doxycycline (20 mg twice

daily) does not lead to a significant increase in bacterial resis-

tance or to a change in fecal or vaginal flora.58, 59

Other Medications to Control MMPsTetracyclines are not the only medications that can prevent

MMP-induced bone erosions. There are promising studies

that show the benefits of TNF-α inhibitors; osteoprotegerin

analogues; HMG-CoA reductase inhibitors (eg, simvasta-

tin); and hormone replacement therapies, including vitamin

D and estradiol.60-63 These medications, along with doxycy-

cline, show great promise in controlling articular bone loss

in the face of inflammation.

ConclusionWhen patients present with condylar resorption, clinicians

have long been resigned to two choices: watch and wait or

surgical resection with the resulting disability and deformity.

Doxycycline is just one pharmacological intervention that


shows promise in curbing the bone loss associated with ar-

thritis and condylar resorption (Figures 6-a, b, c, d, e). ■

Figure 6-a, b, c, d, e This is a 31-year-old patient with condylar resorption secondary to rheumatoid arthritis. She was treated

with orthognathic surgery to correct her malocclusion. The effects of MMPs were controlled pre- and postoperatively by

prescribing the following medications: doxycycline, simvastatin, Enbrel, Feldene, vitamin D, and omega-3 fatty acids. She is 10

months postsurgery with minimal osseous change to her condyles and a stable class I occlusion with good overbite and overjet.


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Summary

IntroductionThe quest to understand the multifaceted movements of

the mandible and its relationship to the rest of the cranial

complex began in the early 1800s.1 Gray’s Anatomy was

one of the first sources to publish the fact that the mandible

moves on a hinge as well as by forward and lateral move-

ments from the condyles in the glenoid fossae.1 Thus, the

temporomandibular joint (TMJ) became known as a gingly-

mo-arthrodial joint and was seen as one of the most complex

joints in the human body. Although the TMJ is considered

a compound joint, it consists of only two actual bones. An

articular disc interposed between the condyles and the man-

dibular fossa of the temporal bone keeps the two bones from

direct articulation. The disc serves as a nonossified bone; it

serves as the third bone of the compound joint and allows

complex movements to occur.2

When occlusal function is ideal, the condyles are po-

sitioned in the glenoid fossae and the mandible should be

able to move by joint-dictated patterns without any interfer-

ence from the teeth.3 According to Okeson, this position is

achieved when the muscles of mastication and the ligaments

combine to seat the condyle into the glenoid fossa.2 Stability

of the joint is maintained by constant muscle activity, even

in resting states, which allows the articular surfaces to come

into contact, although a true structural attachment or union

is not present in the TMJ.2 The muscles play an active role in

the opening and closing of the mandible, while the ligaments

act as passive restraining devices to limit joint movements.

Specifically, the temporomandibular ligament plays a role

in limiting the extent of mouth opening. During the initial

phase of opening, the condyle rotates around a fixed point

for about 20 mm, until the temporomandibular ligament

becomes strained and the condyle is forced into a forward

movement down the articular eminence.2 Posselt defined

this opening as the mandibular terminal hinge opening and

closing.4 The Glossary of Prosthodontic Terms similarly de-

scribes this movement as “an imaginary line around which

the mandible may rotate through the sagittal plane” and

There are many methods of performing a face-bow transfer, but only two

current methods of replicating the position of the maxilla in three planes of

space: with a true hinge face-bow or with an arbitrary earpiece face-bow. The

purpose of this study was to determine if a clinically significant difference in

three planes of space occurs in the mounting of the maxillary cast when the

mounting is done with an arbitrary earpiece face-bow versus a true hinge

face-bow.

The sample consisted of 51 subjects with complete permanent dentitions

through the second molars, including class I, class II, and class III subjects.

Two maxillary impressions were taken on each subject. One maxillary cast

was mounted using an arbitrary earpiece face-bow and the other using a true

hinge face-bow. Each cast was measured and compared in three planes of

space on an adjustable occlusal table containing graph paper. The positions

of the maxillary right central and right and left first molars were recorded for

the true hinge mounting in red on the graph paper and the arbitrary earpiece

face-bow measurements were recorded in blue. The vertical, anteroposterior

(A-P), and transverse differences between the two mountings were recorded,

and a paired t-test was used to analyze the data. The two face-bow techniques

were statistically significantly different in all three planes of space (p ≤ .001).

doRi FReeLand, ddS, [email protected]■ Private Practice, Lake Orion, MI

TheodoRe FReeLand, ddS, mS■ Adjunct Professor, Orthodontic Dept., School of Dentistry, University of Detroit Mercy■ Director Roth/Williams USA ■ Private Practice, Gaylord, MI

RichaRd KuLbeRSh, dmd, mS, PLc■ Program Director, Orthodontic Dept., School of Dentistry, University of Detroit Mercy

RichaRd KaczynSKi, bS, mS, Phd■ Statistician, Dept. of Psychiatry, Yale University School of Medicine

Dori Freeland, DDS, MS ■ Theodore Freeland, DDS, MS

■ Richard Kulbersh, DMD, MS, PLC ■ Richard Kaczynski, BS, MS, PhD

Comparison of Maxillary Cast Positions Mounted from a True Hinge Kinematic Face-Bow vs. an Arbitrary Face-Bow in Three Planes of Space

46 Freeland et al | Comparison of Maxillary Cast Positions

terms the movement the transverse horizontal axis.5

Study of mandibular movements raised questions among

the dental profession as to whether a hinge axis actually ex-

ists, and if so, whether it is one axis or more than one. The

dental profession also debated how accurately the hinge axis

can be located, if in fact one exists; the clinical usefulness of

locating it; and whether an arbitrary point on the face can

satisfactorily be substituted for a specific point as a location

for the hinge axis.6 No other topic inspires more controversy

in oral physiology than the role of the jaw joints in dental

articulation.

Campion, working in 1902, made the first graphic

record of the mandibular movements in a patient. He con-

cluded that both a rotation of the bone on an axis and a

forward-downward movement of the condyles occurred.

Campion designed an adjustable face-bow fixed to the man-

dibular teeth with modeling plaster to graphically record the

various positions of the condyles on the face with a succes-

sion of dots. He concluded that “the only part of the opening

movement which an articulator reproduction is concerned

with is the initial stage, which is seen in the tracings to be a

simple rotation about an axis passing through the condyles.” 7, 8

Bennett also recognized that the mandible was capable of

two independent movements, but he felt that no single fixed

center of rotation for the mandible existed.8 He judged that

the initial center of rotation of the mandible was located be-

hind and below the condyle.8

During this same period, Stallard introduced the term—

and the concept of—gnathology—the study of the harmo-

nious, interrelated functioning of the jaws and teeth.1,7,9 In

1924, McCollum developed the first method of locating the

hinge axis with an instrument called the gnathoscope, and

its later model, the gnathograph.1,7 McCollum demonstrated

that no external anatomical landmarks would indicate the

position of the opening axis, nor could this be done by pal-

pating the joint or by measuring a distance in any direction.1,7

McCollum explained that the hinge axis must be determined

instrumentally, and that the movement of this axis is a com-

ponent of every masticatory movement of the mandible.1,7

After McCollum’s death, Stuart continued to study mandib-

ular movement and developed his own gnathological system,

including a fully adjustable articulator and pantograph.1,7

Gnathologically oriented studies produced and still pro-

duce conflicting conclusions that divide the dental commu-

nity. One group believes that there is a definite transverse

hinge axis, and that it is necessary to find its point of ro-

tation. Another group believes that methods of locating an

arbitrary hinge point are just as reliable, and more operator

friendly. Still others believe that it is not necessary to locate

the transverse axis at all.

Trapozzano and Lazzari found that 57.2% of the sub-

jects in their study had more than one condylar hinge axis

point located on either one or both sides of the mandible.

Therefore, the attempt to locate the hinge axis, was seriously

questioned because multiple axis points may exist.10,11 Other

studies have demonstrated that the center of rotation is mov-

able during every phase of jaw opening and closing; there-

fore these studies also refute the hinge axis theory.12,13 Still

other studies have questioned the use of a hinge axis, due

to the complexity of its location, and the technical operator

error that is inherent in the procedure.14,15 Many investiga-

tors believe that it may be impractical to construct clutches,

locate the hinge axis, make multiple interocclusal records,

and use a fully adjustable articulator on every patient.16 Still

the theory that the hinge axis is a reliable reference—one in

which the position of the maxillary cast on an articulator can

be reproduced—is a very strong one.4

Many studies have demonstrated that the terminal hinge

movements of the mandible pass through both condyles.

These studies support the theory that there is only one hinge

axis .4,17-19 Beard and Clayton reached this conclusion by us-

ing an apparatus that records arcs on paper; they argued that

the terminal hinge axis can be accurately located by finding

the one and only stylus position where no arcing occurs.19

There are many methods of locating the arbitrary hinge

axis for transfer to an articulator. Following are some ex-

amples of these methods.

The Gysi point is located 13 mm in front of the 1.

most upper part of the external auditory meatus on

a line passing to the ectocanthion.

The Lauritzen-Bodner axis is located 12 mm ante-2.

rior to and 2 mm below the porion.

Abdal-Hadi axis is located using a linear regression 3.

formula to predict the anteroposterior (A-P) site of

the hinge point, according to the width profile axis

theory of the face.

The arbitrary hinge axis is located using the ear-4.

piece face-bow. In this method, the ear rods of a

fixed face-bow are inserted into the external audi-

tory meati.

The arbitrary hinge axis is located by external pal-5.

pation of the condylar anatomy.20,21

Studies have shown that when an arbitrary earpiece

face-bow is used to reproduce the condylar positions, the

results are fairly reliable.22-27 Clinically, it has become accept-

able that as long as the arbitrary point is within 5 mm of the

true hinge axis, the arbitrary earpiece face-bow is accurate

enough to study the patient’s occlusion.22-27 Nagy et al con-

ducted another study comparing the location of an anatomi-

cally predetermined hinge axis point with marked hinge axis


points. They found that the mean distance between any two

points was 1.1 mm. More than 96% of predetermined points

were within 2 mm of the true hinge axis.23 Schallhorn also

found that approximately 98% of all true anatomical hinge

axis points were within a 5-mm radius.26

In comparison, studies that compared maxillary cast po-

sitions mounted with four different face-bows showed wide

variation in the mounted maxillary cast positions. All arbi-

trary hinge axis points deviated from the true hinge baseline

point by anywhere from 1.5 mm to 4 mm. Therefore, the

authors of these studies concluded that it was not possible

to establish the clinical superiority of one arbitrary face-bow

over another.28,29

Lauritzen and Bodner located 100 true hinge points on

50 subjects. They found that 67% of the axis points were

5 mm to 13 mm away from the arbitrarily marked hinge

points. This discrepancy may introduce gross errors in the

mounting of the casts on an articulator, resulting in large

occlusal errors.30 Palik et al got similar results. They found

that only 50% of the arbitrary hinge axes located with the

arbitrary earpiece face-bow were within a 5-mm radius of

the terminal hinge axis. This indicated that the arbitrary

earpiece face-bow hinge axis location does not represent the

total population.31 Schulte et al concluded from their study

that errors in locating the arbitrary hinge axis will produce

a three-dimensional occlusal error.32 This study and others

have recommended that if a thick vertical dimension of wax

was used for an interocclusal record, or if the vertical dimen-

sion will be changed with treatment, a true hinge axis should

be located on the patient.32,33 Due to anatomical variations,

the arbitrary earpiece face-bow may introduce significant er-

rors in an A-P or vertical dimension, resulting in mandibular

displacement.34,35 The only way to be relatively certain that

errors due to malpositioning of maxillary casts on an articu-

lator have been avoided is to locate the true hinge axis.30,36-40

Studies indicate that coincidence between the two hinge

axis points does not usually occur.41 This results in a discrep-

ancy between the arbitrary hinge axis and the true hinge axis

points. This discrepancy will cause changes in the mounted

position of the maxillary cast, which in turn can produce a

positional change of all teeth in the three planes of space.41

Zuckerman mathematically demonstrated that discrepancies

between the true hinge axis and the arbitrary hinge axis points

can produce changes in the A-P direction of the occlusion. He

verified in his analog tracing that the arc of the incisal edge

does not change in the A-P direction in centric occlusion, as

long as the mandible is also coincident in centric relation.

However, when an error in the arbitrary hinge axis occurs

and it is anterior to the true hinge, the incisor arc of closure

is anterior to the actual arc of closure.41 Errors in the verti-

cal position of the arbitrary hinge axis (AHA) produce the

largest A-P discrepancies upon mandibular closing.41 Other

authors have graphically illustrated how errors in true hinge

axis location can produce occlusal aberrations.33,35,36,42 These

authors also showed that the greatest errors occurred when

the hinge axis was incorrectly located in a vertical direction

perpendicular to the correct hinge axis closure. An arbitrary

hinge axis positioned superior to the true hinge axis also

produced premature contacts on the anterior teeth. In addi-

tion, if the arbitrary hinge axis was placed inferior to the true

hinge axis, premature posterior contacts occured.33,35,36,42

Brotman’s geometric representation related changes in

the hinge axis point locations between the true hinge axis

and the arbitrary axis to differences produced at the occlus-

al level in mounted casts.43 Brotman concluded that “if the

hinge axis has been improperly located by as much as 3 mm,

the error at the occluding position of the casts (anteroposte-

riorly) will be about .09 mm or less than 1/250 inch.”43

Gordon et al looked at the location of the terminal hinge

axis and its effect on the second molar cusp position on the

position of the second molar cusp.6 Their results showed that

incorrect anterior location of the hinge axis produced the ef-

fect of having moved the mandibular arch backward. Incor-

rect posterior location of the hinge axis produced the effect

of having moved the mandibular arch forward. Incorrect in-

ferior location of the hinge axis caused slight retrusion of the

mandibular cast with premature posterior contacts. Incorrect

superior location of the hinge axis caused protrusion of the

mandibular cast with premature anterior contacts.6

Since studies vary in reporting the percentage of place-

ment of the arbitrary hinge axis less than 5 mm from the true

hinge axis, it can be assumed that larger errors in occlusion

may occur. It has been found that an occlusal discrepancy of

0.01 inch can cause pulpitis or periodontal disease, though

the patient may not be able to detect so small a discrepancy.44

To limit occlusal errors in mountings, it is necessary to locate

the hinge axis to within 1 mm, and the kinematic true hinge

can be done to this degree of accuracy.44 Therefore, the im-

portance of the true hinge axis is substantial when changing

the vertical dimension upon mandibular closure.38

Orthodontics deals specifically with the movement of

all teeth and their occlusal fit. Therefore, it calls for extreme

accuracy during diagnosis, treatment planning, and render-

ing treatment.9 Clinically finding the true hinge axis may be

the only way to ensure a reproducible and accurate starting

point—one from which optimum esthetic and functional re-

sults can be obtained.6,38,45 The purpose of this study was to

compare the maxillary cast mountings of 51 patients in three

planes of space when mounted using a true hinge axis face-

bow versus an arbitrary earpiece face-bow.


A true hinge face-bow was then taken on each subject,

using the true hinge axis instrument (Panadent, Grand Ter-

race, California) (Figure 2). A single operator completed

both face-bow records within 20 minutes of each procedure.

Intraoperator reliability tests for each of the two transfer

techniques were calculated.

Materials and MethodsThe records of 51 patients—34 females and 17 males—treat-

ed in a gnathologically oriented practice constituted the sam-

ple. Subjects ranged in age from 13 to 57 years, and all had

unremarkable medical histories with no contraindications to

orthodontic treatment. All upper and lower permanent teeth,

except third molars, were present on all subjects. TMJ exams

were conducted by a single operator before orthodontic re-

cords were conducted. Evaluation included subjective symp-

tomatology, as well as clinical examination. Subjects who

presented with TMJ symptoms were placed on a gnatho-

logical maxillary splint for a minimum of 3 months, or until

subjects were symptom free. Twenty of the 51 subjects had

records taken after splint therapy. The remaining 31 subjects,

all in active orthodontic treatment and with asymptomatic

TMJ, had records taken one appointment prior to deband.

All subjects had two maxillary alginate impressions tak-

en using Jeltrate alginate (Dentsply, Milford, Delaware). The

impressions were taken using sterilized metal rim lock trays

(Dentsply, Milford, Delaware). All impressions were disin-

fected using Sterall Plus Spray (Colgate-Palmolive Company,

Canton, Massachusetts), and were rinsed with water and air

dried before being poured up.

All impressions were wrapped in moistened paper tow-

els and placed in plastic bags for approximately 20 minutes

prior to being poured up with Velmix (KerrLab, Orange,

California). Each model was poured up utilizing a water-

powder ratio consistent with the manufacturer’s instructions

for Velmix. The Velmix was vacuum mixed to remove any

entrapped air. The models were trimmed, and all bubbles

were removed from the occlusal surfaces.

Arbitrary earpiece face-bow transfers using the external

auditory meati were taken on each subject. (Panadent, Grand

Terrace, California) (Figure 1).

Figure 1-a, b Estimated facebow.

Figure 1-b


One maxillary cast was mounted using the true hinge

kinematic face-bow transfer on a single Panadent articula-

tor (Panadent, Grand Terrace, California), with Snow White

Plaster #2 (Kerrlab, Orange, California) mixed according to

the manufacturer’s instructions. The second maxillary cast

was mounted with the arbitrary face bow on a single Pana-

dent articulator (Panadent, Grand Terrace, California), using

the same mounting plaster as was used for the first cast.

The true hinge maxillary cast was placed on a single

Panadent articulator, and an adjustable occlusal table (Pana-

dent, Grand Terrace, California), with graph paper adhered

to the surface, was attached to the articulator in place of the

mandibular cast. With the occlusal pin at zero, the occlusal

plane relater was stabilized by allowing contact at the maxi-

mum number of maxillary cast teeth (Figure 3).

A 1-mm step ruler (Panadent, Grand Terrace, California)

was used to measure the vertical distance of the mesiobuccal

cusp tip of the right and left first permanent molar and the

upper right central incisor (Figure 4).

Figure 2-a, b True-hinge facebow.

Figure 2-b.

Figure 3 Maxillary cast mounted with occlusal relater and pin at zero.

Figure 4-a Vertical measurements with 1-mm incremental step ruler: Measurement of anterior tooth

vertical discrepancy.

Figure 4-b Vertical measurements with 1-mm incremental step ruler: Measurement of posterior tooth

vertical discrepancy.


This allowed the instrument to register the position of

each tooth on the graph paper (Figure 8).

The occlusal plane relater was left in place, and the same

measuring procedure was then conducted on the maxillary

cast mounted with the estimated face-bow, utilizing blue ar-

ticulating paper. A new sheet of graph paper was adhered to

the occlusal plane relater each time a new set of casts was

measured.

To measure the differences between the red and blue

markings, a Boley gauge was used. Five total measurement

comparisons were done. The first measurement assessed the

change in vertical dimension between the casts at the me-

siobuccal cusp tip of the maxillary right permanent first

molar. The second measurement assessed the vertical dis-

crepancy of the upper left first permanent molar. The third

measurement assessed the vertical discrepancy between the

upper right permanent central incisors. The fourth measure-

ment compared the difference in an A-P direction between

the mesiobuccal cusp tips of the upper right and left first

permanent molars. The fifth measurement assessed the trans-

verse discrepancy between the mesiobuccal cusp tips of the

upper molars. All measurements were conducted by a single

operator. Intraoperator reliability testing was used to vali-

date this measurement technique.

ResultsA two-tailed matched-pairs t-test was used to evaluate for

significant difference in occlusal measurements in three

planes of space between maxillary casts mounted with a true

hinge face-bow and mounted with an estimated face-bow.

For this experiment, an α level of 0.05 was chosen. Given

the number of measurements being evaluated (8), we decided

A straight wire with a 90-degree bend at the tip was

held with the handle parallel to the occlusal plane relater

(Figure 5).

The tip was placed perpendicular to the tooth and held

touching the height of contour of the upper first permanent mo-

lars and the upper right permanent central incisor (Figure 6).

It was then used to mark the position of the mesiobuccal

cusp of the upper molars and the entire incisal-edge position

of the upper central incisor. Red articulating paper for the

maxillary cast mounted with the true hinge axis face-bow

mounted maxillary cast was then placed beneath each tooth

(Figure 7).

Figure 5 Straight-lined measurement instruments.

Figure 6 Articulating paper used with straight-lined measurement instrument for tooth markings.

Figure 7 Tooth markings on graph paper.

Figure 8 Comparing arbitrary hinge axis points vs. true hinge axis point:

1= Lower incisor will arc closed posterior to actual arc of closure if AHA is inferior to TH.

2= Lower incisor will arc closed anterior to actual arc of closure if AHA is superior to TH.

3= Lower incisor will arc closed slightly posterior to actual arc of closure if AHA is anterior to TH.

4= Lower incisor will arc closed slightly anterior to actual arc of closure if AHA is posterior to TH.


to adjust for experimentwide error by reducing our desired

significance level to 0.001.

Table 1 shows the means and standard deviations for

the arbitrary face-bow technique and the true hinge face-

bow technique in the vertical, A-P, and transverse dimensions

with respect to the maxillary right and left first molars and

the maxillary right central incisor. The mean measurements

taken on the cast mounted with a true hinge face-bow were

significantly smaller than those measured on the arbitrary

earpiece face-bow mountings. The standard deviations for

the true hinge face-bow were also one-half to one-third

smaller, indicating less variation around the sample mean.

Results of the paired t-test are shown in Table 2.

The two face-bow techniques differed significantly in

all three planes of space. The mean vertical discrepancy of

the maxillary right first molar between the estimated and the

true hinge face-bow was 2.19 +/- 2.31 (t = 6.76, df = 50, p

< .001). The mean vertical discrepancy for the maxillary left

first molar was 2.45 +/- 2.21 (t = 7.90, df = 50, p < .001).

The mean vertical discrepancy for the upper right central

was 1.90 +/- 1.75 (t = 7.76, df = 50, p < .001).

The mean difference in the A-P dimension was 3.82 +/-

5.51 (t = 8.163, df = 50, p < .001) for the maxillary right first

molar and 3.10 +/- 2.63 (t = 8.28, df = 50, p < .001) for the

maxillary left first molar. The maxillary right central incisor

showed a mean difference of 3.05 +/- 2.62 (t = 8.25, df = 50,

p < .001). Finally, the transverse dimension was evaluated.

The mean difference for the maxillary right first molar was

2.23 +/- 1.33 (t = 12.11, df = 50, p < .001). The mean differ-

ence for the maxillary left first molar was 2.60 +/- 1.49 (t =

11.57, df = 50, p < .001).

The measurement differences in the vertical direction of

the maxillary right first molar ranged from 0.0 to 3.0 mm.

The measurement differences in the vertical direction of the

maxillary left second molar ranged from 1.0 mm to 3.0 mm.

The measurement differences in the vertical direction of the

maxillary upper right central incisor ranged from 0.0 to 5.0

mm. The differences in the A-P dimension of the upper right

molar ranged from 0.0 to 13.1 mm; of the upper left molar

from 0.0 to 15.0 mm; and of the upper central incisor from

0.0 to 13.0 mm. The differences in the transverse dimension

ranged from 0.0 to 7.0 mm for the upper right first molar

and from 0.5 to 7.9 mm for the upper left first molar.

DiscussionMounting dental casts on an articulator allows the clinician

to simulate maxillo-mandibular position in centric relation

and makes possible a visible simulation of mandibular bor-

der movements. It has been recommended that mounting

diagnostic dental casts on an articulator should be incorpo-

rated into routine clinical orthodontic practices.3,46 Record-

ing the hinge axis and transferring it to an articulator is of

considerable value in the diagnosis and treatment of occlusal

malfunction.42 In this diagnostic process, a face-bow trans-

fer is one of the first steps in taking accurate intermaxillary

records. Many face-bow techniques are in use today.20,21

However, this study conducted a comparison of only two

face-bow techniques, an arbitrary earpiece face-bow and a

true hinge face-bow.

The null hypothesis for this study: “There is no differ-

ence in the vertical, horizontal, or transverse position of the

maxillary cast mounted with a true hinge face-bow versus an

arbitrary earpiece face-bow” was rejected. Paired t-tests indi-

cated that the maxillary cast position using an arbitrary face-

bow transfer was significantly different in all three planes of

space from the maxillary cast position mounted using a true

hinge face-bow transfer.

In previous comparison studies when the arbitrary ear-

piece face-bow is located anywhere along a 5-mm radius of

the true hinge axis point, some authors have found that the

mandibular arc of closure may not be very different from the

true hinge arc of closure.21,26,39,40,42 However, Lauritzen and

Bodner found that in only 33% of the 50 patients they ex-

amined did the arbitrary hinge point fall within 5 mm of the

true hinge point. In the other 67%, the arbitrary hinge points

were 5 mm to 13 mm away from the true hinge points. Ar-

bitrary markings of the hinge axis introduce severe errors

in mounting casts on an articulator, which may introduce

occlusal errors in the centric jaw relation record.30 Ricketts

Table 1 Mean values of the two face-bow techniques.

Table 2 Paired t-tests for differences between estimated and true hinge technique.

Measurements


found that there can be extreme variation in the soft tissue

around the ear.34 This variation can make it difficult to lo-

cate the hinge point with an arbitrary earpiece face-bow.

The present study found larger mean values for the arbitrary

earpiece face-bow measurements. This suggests that the true

hinge face-bow may not be as sensitive to anatomical chang-

es as the arbitrary earpiece face-bow.

Goska and Christensen conducted a similar study to

to the present study, in which they compared the positions

of maxillary cast permanent first molars in three planes of

space, using four different face-bow techniques. A true hinge

face-bow determined axis point was chosen as a baseline

against which to compare the other three arbitrary face-bow

techniques.28 They found that deviations between this base-

line and the other three face-bow mountings ranged from 1.5

mm to 4 mm.28 They found that deviations between the true

hinge face-bow and the arbitrary earpiece face-bow ranged

from 1.9 mm to 3.8 mm. Like the authors of the present

study, they concluded that variations in the arbitrary ear-

piece face-bows might have resulted from naturally occur-

ring variations in ear anatomy or the fact that the arbitrary

earpiece face-bow is an average measurement.28

In general, the present study suggests that error intro-

duced from arbitrary earpiece face-bow hinge axis location

may produce occlusal discrepancies caused by malposition-

ing of the maxillary cast. The present study differs from

other previous studies in that it evaluates changes at the

occlusal level of the maxillary cast, as opposed to looking

at the joint level when comparing arbitrary and true hinge

mounting techniques. This study also differs from previous

studies in that it does not measure the occlusal discrepan-

cies that result from contacts during the mandibular arc of

closure, since the mandibular cast was not incorporated into

the measurements.

Zuckerman, in analog tracing the arc of the incisal edge,

verified that no A-P change occurred in the arc of closure, as

long as the mandible rotated along the accurate hinge axis.

However, when an error in the arbitrary earpiece face-bow

hinge axis occurred anterior to the true hinge, the incisor arc

of closure was anterior to the actual arc of closure, and when

the arbitrary earpiece face-bow hinge axis occurred posterior

to the true hinge axis, the opposite effect occurred. Errors in

the vertical position of the arbitrary earpiece face-bow hinge

axis were found to produce the largest A-P discrepancies

upon mandibular closing41 (Figure 9).

Zuckerman found that an anterior incisor displacement

of 1.5 mm could occur if the arbitrary hinge axis was off from

the true hinge axis by approximately 10 mm.41 Although the

method for the present study does not incorporate the man-

dibular cast arc of closure, wax bite thickness, or condylar

positioning, it is interesting to note that the largest discrep-

ancy in maxillary cast position occurred in the A-P direction

with a mean difference greater than 3 mm in all three areas

measured (maxillary right and left first permanent molar and

the upper right permanent central incisor).

Gordon et al conducted a mathematical study to calcu-

late the amount of cusp height and mesiodistal error at the

second molar that results from arbitrary earpiece face-bow

hinge axis location 5 mm and 8 mm anterior, superior, pos-

terior, and inferior to the true hinge axis.6 They concluded

that incorrect location of the hinge axis caused a positional

change in the occlusal relationship between the maxilla and

the mandible, resulting in various premature contacts. De-

Figure 9-a True hinge mandibular cast vs. estimated hinge maxillary cast: True hinge mounting.

Figure 9-b True hinge mandibular cast vs. estimated hinge maxillary cast: Estimated hinge mounting substituted for true

hinge maxillary mounting.


pending upon the direction in which the arbitrary earpiece

face-bow hinge axis was displaced from the true hinge axis,

the premature contacts occurred either anterior or posterior

to the actual arc of closure. Total error that could occur at

the second molar cusp ranged from 0.15 mm of open cuspal

space to 0.4 mm of excess cuspal height. The mesiodistal

error of the second molar cusps ranged from 0.51mm to-

ward the distal to 0.52 mm toward the mesial.6 Brotman also

found that a 0.09-mm A-P discrepancy would occur between

occluding casts if the arbitray earpiece face-bow hinge axis

was improperly located by as much as 3 mm from the true

hinge point. Brotman concluded that if the arbitrary earpiece

face-bow hinge axis is incorrectly placed superior to the true

hinge axis, the lower cast will occlude in a more protrusive

direction, with premature contacts on the anterior teeth.

If the arbitrary earpiece face-bow hinge axis is incorrectly

placed inferior to the true hinge axis, the lower cast will oc-

clude in a more distal direction, with premature contacts on

the posterior teeth.43 This conclusion resembles the findings

of Gordon et al. Weinberg and Fox drew similar conclusions;

the values they obtained for calculated horizontal error in

cusp heights closely resembled each other.35,44 This suggests

that errors of several millimeters in axis location might pro-

duce occlusal errors that are clinically intolerable on the part

of the patient.43

The authors of the present study found a mean differ-

ence in incisor position of 3.04 mm. The occlusal discrepan-

cies found in the present study suggest that a range greater

than 5 mm existed between hinge axis points located with

the arbitrary earpiece face- bow mounting and the true hinge

face-bow. The discrepancy in maxillary cast position found

in this study might possibly introduce a change in the clo-

sure of the mandible into occlusion. The problems caused

by the occlusal errors resulting from inaccurate location of

the hinge axis point are illustrated in Figure 10. The photos

suggest an exaggerated discrepancy between the two casts

because two completely different face-bow techniques were

used. They serve to illustrate occlusal error that may result

from error in maxillary cast position. In some cases, how-

ever, the autorotated mandibular casts closed with only a

small degree of occlusal error (Figure 9). Other casts showed

severe positional changes resulting in larger occlusal errors

when this was attempted. (Figure10).

It may be difficult to detect which patients have arbi-

trary earpiece face-bow hinge points naturally located within

5 mm of their true hinge point. Therefore, if any degree of

accuracy is needed or if any change in vertical dimension,

such as an occlusal equilibration or orthognathic surgery, is

planned, use of a true hinge axis face-bow should be con-

sidered. Previous studies have suggested that location of a

kinematic true hinge axis point prior to treatment for dentu-

lous patients who require extensive treatment saves time and

results in a more satisfactory occlusion.6 The present study

found a statistically significant difference in the maxillary

cast position in all three planes of space between the two

face-bow techniques compared.

Conclusions1. Statistically significant differences (p < .001) were

found between the true hinge face-bow mounted maxillary

cast and the estimated earpiece face-bow hinge mounted max-

Figure 10-a Mounted maxillary estimated cast vs. true hinge mounted maxillary cast: True hinge mounting.

Figure 10-b Mounted maxillary estimated cast vs. true hinge mounted maxillary cast: Estimated hinge mounting

substituted for true hinge maxillary mounting.


illary cast in the vertical dimension, with a mean of 2.19 mm

for the maxillary right first molar, 2.45 mm for the maxillary

left first molar, and 1.90 mm for the maxillary right central

incisor.

2. Statistically significant differences (p < .001) were


cast and the estimated earpiece face-bow hinge mounted

maxillary cast in the A-P direction, with a mean difference

of 3.82 mm between the maxillary right first molars, 3.10

mm between the maxillary left first molars, and 3.05 mm

between the maxillary right central incisors.

3. Statistically significant differences (p < .001) were


cast and the estimated earpiece face-bow hinge mounted

maxillary cast in the transverse dimension, with a 2.23-mm

difference between the maxillary right first molars and a

2.60-mm difference between the maxillary left first molars.

4. This study found that there is a significant differ-

ence between the arbitrary earpiece face-bow hinge axis and

the true hinge face-bow hinge aixs. Thus, when an arbitray

earpiece face-bow hinge axis transfer is used, the maxillary-

mandibular complex is placed in an incorrect position in the

articulator. The end result is a lack of functional harmony. ■

References 1. McCollum BB. The mandibular hinge axis and a method of locating it. J Prosthet Dent. 1960;(10): 430-435.

2. Okeson JP. Functional Anatomy and Biomechanics of the Mastica-tory System: Management of Temporomandibular Disorders and Oc-clusion. 4th ed. St. Louis, MO: Mosby; 1998: 3-38.

3. Roth RH. Functional occlusion for the orthodontist. J Clin Orthod. 1981;(15):32-51.

4.Posselt, U. Terminal hinge movement of the mandible. J Prosthet Dent. 1957;(7): 787-796.

5. Glossary of prosthodontic terms. J Prosthet Dent. 1987; (58): 721.

6. Gordon SR, Stoffer WM, Connor SA. Location of the terminal hinge axis and its effect on the second molar cusp position. 1984;(52): 99-105.

7. Starcke EN. The history of articulators: from face-bows to the gnathograph, a brief history of early devices developed for recording condylar movement, Part II. J Prosthet Dent. 2002;(11): 53-62.

8. Winstanley RB. The hinge-axis: a review of the literature. J Oral Rehab. 1985;(12): 135-139.

9. Klar NA, Kulbersh R, Freeland TD, Kaczynski R. Maximum tntercus-pation- centric relation disharmony in 200 consecutively finished cases in a gnathologically oriented practice. Semin in Orthod. 2003;(9): 109-116.

10. Trapozzano VR, Lazzari JB. The physiology of the terminal rotational position of the condyles in the temporomandibular joint. J Prosthet Dent. 1967;(17): 122-133.

11. Trapozzano VR, Lazzari JB. A study of hinge axis determination. J Prosthet Dent. 1961;(11): 858-863.

12. Ferrario VF, Sforza C, Miani A, Serrao G, Tartaglia G. Open-close movements in the human temporomandibular joint: does a pure rotation around the intercondylar hinge axis exist? J Oral Rehab. 1996;(23): 401-408.

13. Hellsing G, Hellsing E, Eliasson S. The hinge axis Concept: a radio-graphic study of its relevance. J Prosthet Dent. 1995; (73): 60-64.

14. Bowley JF, Michaels GC, Lai TW, Lin PP. Reliability of a face-bow transfer procedure. J Prosthet Dent. 1992;(67): 491-498.

15. Bowley JF, Pierce CJ. Reliability and validity of a transverse hori-zontal axis location instrument. J Prosthet Dent. 1990;(64): 646-650.

16. Strohaver, RA. A comparison of articulator mountings made with centric relation and myocentric position records. J. Prosthet Dent. 1972;(28): 379-390.

17. Aull AE. A study of the transverse axis. J. Prosthet Dent. 1963;(13): 469-479.

18. Borgh O, Posselt U. Hinge axis registration: experiments on the articulator. J Prosthet Dent. 1958;(8): 35-40.

19. Beard CC, Clayton JA. Studies on the validity of the terminal hinge axis. J Prosthet Dent. 1981;(46): 185-191.

20. Abdal-Hadi L. The hinge axis: evaluation of current arbitrary determination methods and a proposal for a new recording method. J Prosthet Dent. 1989;(62): 463-467.

21. Razek MKA. Clinical evaluation of methods used in locating the mandibular hinge axis. J Prosthet Dent. 1981;(46): 369-373.

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56 Notes

Notes


Summary

IntroductionTooth attrition is classified as tooth disease under the Inter-

national Classification of Diseases, published by the World

Health Organization. According to Jablonski, tooth attrition

takes place when tooth-to-tooth contact, as in mastication,

occurs on the occlusal, incisal, and proximal surfaces.1 It is

differentiated from tooth abrasion (the pathologic wearing

away of the tooth substance by friction, as brushing, brux-

ism, clenching, and other mechanical causes) and from tooth

erosion (the loss of substance caused by chemical action

without bacterial action).

In reality, the wear may be related to a combination of

factors including attrition, abrasion, and erosion; that is,

physical-mechanical and chemical effects can have an impact

on the loss of physiologic and habitual tooth surface mor-

phology.2 Grippo et al state that three physical and chemical

mechanisms are involved in the etiology of tooth surface le-

sions. These mechanisms are stress, corrosion, and friction.

The various types of dental lesion are caused by these mecha-

nisms acting either alone or in combination. Friction, includ-

ing abrasion (which is exogenous) and attrition (which is

endogenous), leads to the dental manifestation of wear. Cor-

rosion leads to the dental manifestation of chemical or elec-

trochemical degradation. Stress, which results in compres-

sion, flexure, and tension, leads to the dental manifestation

of microfracture.3

Loss and excessive wear of hard dental tissues is a per-

manent problem of the dentition, especially in the modern

man; it is found in almost all age groups. Tooth wear is an

inherent part of the aging process; it occurs continuously but

slowly throughout life. In some individuals, tooth wear oc-

curs more rapidly than in others, leading to severe morpho-

logic, functional, and vital damage to the teeth, which cannot

be considered normal.4 Hand et al found that in a sample of

520 adults, 84.2% had enamel attrition, 72.9% had dentin

attrition, and 4.2% had severe attrition.5 In cases of severe

attrition, Sivasithamparam et al found that 11.6% of 448

adult patients had either near-pulpal exposures or frank pul-

pal exposures.6

Schneider and Peterson found that 15% of children

demonstrate tooth wear due to bruxism.7 Most of the preva-

lence studies in Europe and North America indicate that the

prevalence of wear on enamel in children is common (up to

60% involvement), while the prevalence of exposed dentin

varies from 2% to 10%.8,9

Malocclusion and occlusal interference in excursive movement is the major

cause of pathologic tooth wear. Tooth wear starts with shortening of the an-

terior teeth. As interference in mandibular movement increases, the posterior

teeth gradually become more flat. Recognizing tooth wear before and after

orthodontic treatment is important for retention of the treated result and for

ensuring functional occlusion. For this reason, orthodontic treatment should

be detailed and completed with restorative rehabilitation of the lost tooth

material.

Jina Lee LinTon, ddS, ma, Phd, [email protected]■ Graduated from Yonsei University (DDS, PhD), 1986 ■ Graduated from Columbia University, SDOS, 1988■ Graduated from Columbia University Orthodontic Department (MA), 1991■ Private Practice in Seoul, Korea, 1991–present

WoneuK JunG, ddS■ Graduated from Dan Kook University, 1991 ■ Private practice in Seoul, Korea, 1991–present

Jina Lee Linton, DDS, MA, PhD, ABO ■ Woneuk Jung, DDS

The Effect of Tooth Wear on Postorthodontic Pain Patients: Part 2

58 Linton, Jung | The Effect of Tooth Wear on Postorthodontic Pain Patients: Part 2

Case ReportsThe six cases below show individual clinical cases with vari-

ous severity of attrition with or without treatment.

Case 1: Attrition Occurred With no Orthodontic TreatmentAn 11-year-old female came in for checkup in April 2006,

at which time the upper lateral incisor edges and canine tips

showed wear (Figure 1). She had class I canine and molar

relationships and a 3-mm overbite and overjet (April 2006).

When she came back for orthodontic treatment 3 years later

(January 2009), the wear on the laterals and canines had

progressed significantly (red arrows).

Case 2: Attrition Occurred During Orthodontic Treatment A 12-year-old male had a crossbite on the left laterals and an

open bite on the central incisors (Figure 2). His canines and

molars were in class I relationship (September 2002). After

a year and a half without treatment, the upper left canine

showed slight wear on the mesial side (January 2004). Af-

ter 8 months of fixed appliance therapy, that canine showed

marked flattening on the tip (October 2004).

Figure 1 Attrition occurred with no orthodontic treatment.

Figure 2 Attrition occurred during orthodontic treatment.

Case 3: No Attrition Occurred During Orthodontic Treatment A 17-year-old male had class II div. 2 malocclusion (Figure

3) and displayed no wear on the upper right canine tip (Sep-

tember 1995). After 22 months of treatment with mandibu-

lar advancement surgery, the sharp canine tip remained (July

1997).

Case 4: Slight Attrition Occurred During Orthodontic TreatmentA 13-year-old male with class I malocclusion came in pre-

sented with sharp upper canine tips (June 1998). After 1½

years of fixed-appliance therapy (January 2000), the right

canine tip remained intact (blue arrow), while the left ca-

nine tip showed wear. A photograph taken 2 years post-

treatment (January 2002) showed wear on the right canine

tip (Figure 4).

Figure 3 No attrition occurred during orthodontic treatment.


Figure 4 Slight attrition occurred during orthodontic treatment.

Case 5: No Attrition Occurred During or Following Orthodontic TreatmentA 24-year-old female came in for treatment of bimaxillary

dentoalveolar protrusion (June 1998). The canine tip re-

mained the same immediately after orthodontic treatment

(April 2001) and 7 years posttreatment (April 2008). This pa-

tient had no apparent anterior tooth attrition over the 10-year

observation period (Figure 5). On lateral excursive movement,

canine guidance existed with adequate separation of posterior

teeth on both the chewing and the nonchewing sides.

Figure 5 No attrition occurred during or after orthodontic treatment.

Case 6: Attrition Occurred During Orthodontic TreatmentA 13-year-old male came to the clinic in January 2000 for

treatment of protruding upper incisors. The patient’s face

showed a protrusive upper lip and a normal-size mandible,

with no apparent asymmetry. He had class II malocclusion

with maxillary dentoalveolar protrusion, severe crowding

in the upper and lower arches, and a constricted maxillary

arch. The upper right canine had not erupted due to lack of

space, even though the root had almost formed (Figure 6).

Figure 6 Preorthodontic treatment photographs and x-rays.

Figure 6-a Front facial smiling photograph.

Figure 6-b Lateral facial photograph showing lip protrusion and strained

mentalis muscle.

Figure 6-c Right lateral intraoral photograph showing class II molar relationship in MIP.

Figure 6-d Front intraoral photograph in MIP showing crowding and crossbite in the upper right lateral incisor.


The maxillary arch was rapidly expanded with a fixed-

type expander, which was retained for 6 months. Growth

modification of the maxillary protrusion was accomplished

simultaneously with a high-pull headgear for 10 months. The

diagnostic study models mounted before and after headgear

therapy clearly showed the effect of the growth modification

treatment (Figure 7).

Subsequent to headgear therapy, the four first premo-

lars were extracted, and the patient received fixed-appliance

therapy for the following 20 months. Class I canine and

molar relationships were achieved with maximum anchor-

age in the upper arch and moderate anchorage in the lower

arch in December 2002. The patient’s facial appearance was

Jarabak’s cephalometric analysis showed a strong coun-

terclockwise growth tendency expressed in such measure-

ments as a posterior facial height-anterior facial height ratio

of 70%, a long ramus height in comparison to the posterior

cranial base length, and a small Y-axis-to-SN angle (Table 1).

Figure 6-f Panoramic x-ray. The upper left canine showing root apex almost formed, but not erupted, due to lack of space.

Figure 6-g Lateral cephalogram showing slightly retrusive mandible and protrusive upper incisors.

Figure 6-e Left lateral intraoral photograph in MIP showing class II molar relationship and retained deciduous canine.

Table 1 Jarabak’s analysis of case 6 in January 2000.

Figure 7 Mounted models of the case before and after the first phase of growth modification treatment. The models were

mounted on a semiadjustable articulator with estimated face-bow transfer and with centric relation bite registration

records. The class II relationship of the first molars (blue lines) in January 2001, was improved compared to the molar

relationship of the case in January 2000.


improved, with retraction of the upper anterior teeth and

favorable mandibular growth (Figure 8).

Figure 8 Postorthodontic treatment records.

Figure 8-a Front facial smiling photograph.

Figure 8-b Lateral facial photograph showing

improvement in profile compared to Figure 1b.

Figure 8-c Right lateral intraoral photograph showing that class I canine and molar relationships were achieved.

Figure 8-d Front intraoral photograph showing that approximately 2 mm of overjet was achieved.

Figure 8-e Left lateral intraoral photograph showing that class I canine and molar relationships were achieved.

Figure 8-f Maxillary arch showing alignment without any extraction spaces left.

Figure 8-g Panoramic x-ray showing overcorrection in root angulation of the canines and developing third molars.


Figure 8-h Lateral cephalogram.

Figure 8-i Superimposition of cephalometric tracings before (black line) and after (red line) orthodontic treatment shows that maximum anchorage control of the upper molars was

accomplished. The maxilla and the mandible grew downward and forward as predicted.

The patient returned to the clinic for correction of lower

anterior tooth crowding at age 20 in April 2008 (Figure 9).

Figure 9 Four-year retention photographs.

Figure 9-a Front facial smiling photograph showing well-developed gonial angle.

Figure 9-b Lateral facial photograph.

Figure 9-c Right lateral intraoral photograph showing that class I canine and molar relationships were retained.

Figure 9-d Front intraoral photograph showing that the lower dental midline was shifted 2 mm to the left.


Figure 9-e Left lateral intraoral photograph showing end-on class II canine relationship.

Figure 9-f Panoramic x-ray.

Figure 9-g Lateral cephalogram.

Figure 9-h Superimposition of the cephalometric tracings after orthodontic treatment (red line) and 4-year retention

(green line), showing that there was little change in the soft-tissue and hard-tissue structures.

Upon clinical examination, wear on the maxillary canine

tips was noted as being quite severe for his age. Upon further

questioning, the patient complained of occasional headache

and pain in the area of the temporomandibular joint (TMJ).

His static occlusion showed 1.5 mm of overbite at the central

incisors and no overbite on the left lateral incisor. The lower

anterior teeth were tipped to the left side, resulting in a lower

midline shift to the left side. Dentin exposures were pres-

ent on the upper lateral incisal edges and the lower anterior

teeth. The upper and lower first molars also showed marked

wear on the cusp tips. Upon excursive movement of both

right and left sides of the madible, the posterior teeth on the

chewing side showed simultaneous contacts—that is, group

function—and teeth on the nonchewing side showed harm-

ful contacts (Figure 10).


The patient’s records were reviewed to compare the

amount of tooth wear at age 15 immediately after orthodon-

tic treatment (December 2002) with the amount of tooth

wear at age 20 (Figure 11).

The canine tips already showed wear at age 15. Progres-

sion of tooth wear was evident; 1.5 mm of vertical overbite in

the upper and lower canines in December 2002 was reduced

down to minimum vertical overbite in April 2008. The oc-

clusal views showed the beginning of dentin exposure on the

upper lateral incisors and the canines. The first molar wear

caused no obvious incisal changes but the progression of the

wear was definitely observable as wider wear facets and dim-

ples on the molar cusp tips in April 2008 (Figure 12).

Figure 10 Mandibular movements.

Figure 10-a Due to wear on the canine tip, there are multiple tooth contacts on the right chewing side and harmful contacts

on the left nonchewing side during the right chewing movement.

Figure 10-b Incisive movement indicates multiple contacts on the posterior teeth.

Figure 10-c Due to wear on the canine tip, there are multiple tooth contacts on the left chewing side and harmful contacts on

the right nonchewing side during the left chewing movement.

Figure 11 Comparison of tooth wear over a 5-year period. Progression of tooth wear from 1.5 mm of vertical overbite in the upper and lower canines in December 2002 down to

minimum vertical overbite in April 2008. (Red arrows indicate flattened anterior teeth.)

Figure 12 Occlusal views of tooth wear. Wear on the posterior teeth is less apparent than wear on the anterior teeth. On close

examination, tooth wear (red arrows) is shown as facets or dimples on the cusp tips.


the wear progressed during the fixed-appliance therapy. In

the absence of anatomy at the cusp tips and incisal edges, as

in Figures 3-c and 3-e, proper anterior guidance and canine

guidance in movement would not have taken place (Figure

14). This in turn would have caused further wear with the

passage of time, as shown in Figures 6 and 7.10

Stable condylar position (SCP) could not be recorded in

the presence of dysfunction of the masticatory system,11 so

a maxillary anterior-guided orthosis12 was prepared and the

patient wore it for 2 months, until all clinical signs and symp-

toms of TMJ dysfunction disappeared. The orthosis (Figure

15) allowed the condyles to assume their superior, anterior,

and medial (SAM) positions in intimate contact with the

thinnest part of the biconcavity of the disc, and made pos-

sible the diagnosis of a SCP from the maximum intercuspal

position (MIP). The SCP was recorded with Axi-Path record-

ing, so the mounted models would arc close in centric.13,14

All available intraoral photographs that had been taken

in the past were put together to analyze the event of tooth

wear in this patient (Figure 13).

The upper right canine showed no wear before the

initial stage of fixed-appliance therapy in June 2001. The

canine wear occurred sometime during the following 8

months, and further wear seemed to have occurred between

February 2002 and December 2002. The upper left canine

erupted with sharp anatomy in May 2000. However, the tip

was worn down already on the day of bracket bonding, and

Figure 13 The event of upper canine wear during orthodontic treatment. The right canine shows definite wear (red arrows)

during fixed-appliance therapy. The sharp anatomy (blue circle) of the left canine tip at the time of eruption is shown in the

photograph (May 2000). It was gone before the fixed-appliance therapy.

Figure 14 Mandibular movement of the mounted models.

Figure 14-a Intraoral movement shown in Figure 5-a was reproduced with models mounted on a semiadjustable

articulator in SCP. There were nonchewing-side interferences of the functional cusps of the upper left molars (red arrows).

Figure 14-b Intraoral movement shown in Figure 5-b was repro-duced using models. There were nonchewing-side interferences of the functional cusps of the right upper molars (red arrows).

Figure 15 Maxillary anterior guided orthosis. The patient wore the removable plate continuously until all the

symptoms disappeared and SCP was obtained.


Subtractive coronaplasty15 was done on the posterior

teeth to achieve equal stops and maximum intercuspation in

SCP, and to preserve the natural tooth forms (Figure 16).

Anterior maxillary and mandibular teeth were built up

with wax on the diagnostic casts to relegate all eccentric

tooth contacts to the anterior teeth (Figure 17).

The additive coronaplasty was done by duplicating the

wax-up of the casts on the anterior teeth with composite

resin (Figure 18).16

Figure 16 Before and after coronaplasty.

Figure 16-a The maxillary arch after coronaplasty shows that coronaplasty does not necessarily flatten the occlusal

surfaces. Rather, it can redefine the anatomy.

Figure 16-b The mandibular arch after coronaplasty also shows redefined anatomic form of the posterior teeth.

Figure 17 Wax-up on the mounted model to achieve 3 mm to 4 mm of vertical overbite and 2 mm to 3 mm of horizontal overjet.

Figure 18 Additive coronaplasty was done with a hybrid-type composite resin on each anterior tooth according to the

wax-up in Figure 12.

The average unworn maxillary central incisor is approx-

imately 12 mm and the mandibular central incisors are 10

mm according to the American Academy of Cosmetic Den-

tistry (AACD). In the patient’s case, they were 12 mm and

7.7 mm and were restored to 12.3 mm and 9.8 mm respec-

tively (Figure 19).17

According to Lee, adequate anterior guidance can be ob-

tained with incisor vertical overlap of 3 mm to 4 mm and

horizontal overlap of 2 mm to 3 mm.18 Initially in April 2008

the patient’s MIP and SCP did not coincide and his overjet

was 2 mm. In SCP the overjet increased to 3.5 mm, which was

corrected to 2 mm with additive coronaplasty (Figure 20).

Only after additive coronaplasty could a complete elimi-

nation of eccentric occlusal interferences be achieved with

excursive movements of the mandible (Figure 21).

Figure 19 Measurements of the teeth before and after positive coronaplasty. The upper central incisors were 12.0 mm long

and became 12.3 mm long. The lower central incisor was 7.7 mm long and became 9.8 mm long.

Figure 20 Overjet change after coronaplasty. When MIP and SCP did not coincide, the overjet was 2 mm. In SCP, the overjet increased to 3.5 mm, which was corrected

to 2 mm with additive coronaplasty.


Figure 21 Mandibular movement after coronaplasty.

Figure 21-a In the right chewing movement, both the chewing and the nonchewing sides show sufficient clearance between

the upper and lower posterior teeth (blue arrows).

Figure 21-b In the left chewing movement, both the chewing and the nonchewing sides show sufficient clearance (blue arrows).

With coronaplasty the patient’s bite was stable, and the

patient was pleased with his smile and with the overall ap-

pearance of his face (Figure 22).

The abnormal tooth wear the patient demonstrated be-

fore coronaplasty was due to improper incisal guidance and

canine guidance. Since tooth wear progresses much faster in

the dentin layer than in enamel, his entire dentition would

have become significantly shorter over the next 10 to 20

years, if no intervention had taken place. The patient’s oc-

clusion was completed with coronaplasty, and the longevity

and stability of his dentition were greatly enhanced.

DiscussionAt the present, the majority of dentists believe that teeth

can successfully compensate for the loss of tissue by migra-

tion and elongation, and that these do not disturb the basic

functions of the masticatory system (mastication, speech,

and swallowing).19 However, some researchers have argued

that anatomical tooth form plays an important role in the

proper function of the masticatory system.17,18 Knight and

et al conducted a longitudinal study on 223 orthodontically

treated patients 20 years posttreatment. They found that

there was a strong relationship between incisal and occlus-

al tooth wear during the mixed dentition and subsequent

wear of the adult dentition.20 Tooth wear that occurred dur-

ing the mixed dentition in these subjects actually occurred

on the permanent incisors. Even though the malocclusion

was corrected, the loss of tissue due to wear in the previ-

ously affected teeth persisted. Consequently, the patients’

incomplete anterior and canine guidance systems continued

to influence their permanent dentition.

Figure 22 Comparison of the case before and after coronaplasty.

Figure 22-a Full-smile facial photograph taken after coronaplasty shows that the patient’s smile became

more esthetically pleasing.

Figure 22-b Lateral facial photographs taken before and after coronaplasty show little change.

With regard to interferences in mandibular movement,

Masatoshi and Masanori studied occlusal factors in relation

to TMD in 146 young adults; they concluded that molar-

guided occlusion patterns were associated with a high risk

of TMD.21 All subjects with TMD had nonchewing interfer-

ences in border excursions and in tooth-dictated excursions.

Without additive coronaplasty to restore the lost volume of

tooth material, complete elimination of interferences may

not be possible, nor may it be possible to maintain the op-

timal health of the teeth.16 As we saw in case 6, the teeth

were too worn down to allow for adequate function, and

the post-orthodontic result was an incomplete occlusion vul-

nerable to relapse. The patient’s TMJ symptoms would have

persisted, and the attrition process would have accelerated

once the dentin layer was exposed. Tooth wear that occurred

while the patient was receiving treatment was unavoidable in

this case. Early intervention of malocclusion in mixed denti-


tion might have enabled us to circumvent pathologic tooth

wear while the patient was undergoing treatment?

In canine guidance, the horizontal forces are minimized

by limiting the contact of the supporting cusps with their op-

posing fossae at or near their intercuspal position. All other

lateral contacts are prevented by the steeper inclination of

the canines. This causes the chewing movement to be more

vertical in the frontal view. Case 5 exemplifies the preserva-

tion of tooth material in the presence of functional occlu-

sion. Upon lateral excursive movements, the canine guidance

provided sufficient clearance in the posterior teeth.

Many of our orthodontic patients already have worn

canines and incisors. Occlusal interferences, premature con-

tacts, and habitual bruxism and/or clenching all may act as

stressors. Tooth contact during swallowing occurs 2,400

times a day, according to Straub23 and Kydd.24 These repeti-

tive static and cyclic occlusal loads could also cause wear

on the anterior, as well as the posterior, teeth. Although it is

difficult to quantify the amount of tooth wear precisely, es-

pecially in cross-sectional studies, orthodontists can appraise

attrition of the incisal edges and canine tip most easily from

intraoral photographs. Why should orthodontists be aware

of tooth wear? What happens if the dentist ignores if they

ignore the problem? These are important questions, because

any patient who is not informed of tooth surface loss is put

at risk of having no choice in treating what can become a

severe condition. ■

References1. Jablonski, S. Jablonski’s Dictionary of Dentistry. 2nd ed. Philadel-phia: Saunders, 1992.

2. Litonjua L, Andreana S, Bush PJ, et al. Tooth wear: attrition, erosion, and abrasion. Quintessence Int. 2003;(34):435-446.

3. Grippo J, Simring M, Schreiner S. A new perspective on tooth sur-face lesions. J Am Dent Assoc. 2004;135(8):1109-1118.

4. Badel T, Keros J, Šegović S, Komar D. Clinical and tribological view on tooth wear. Acta Stomatol Croat. 2007;41(4):355-365.

5. Hand J, Beck J, Turner K. The prevalence of occlusal attrition and considerations for treatment in a noninstitutionalized older population. Spec Care Dentist. 1987;(7):202-206.

6. Sivasithamparam K, Harbrow D, Vinczer E, et al. Endodontic seque-lae of dental erosion. Aust Dent J. 2003;(48):97-101.

7. Schneider P, Peterson J. Oral habits: considerations in management. Pediatr Clin North Am. 1982;(29):523-546.

8. Dugmore C, Rock W. The prevalence of tooth erosion in 12-year-old children. Br Dent J. 2004;196(5):279-282.

9. Bardsley P, Taylor S, Milosevic A. Epidemiological studies of tooth wear and dental erosion in 14-year-old children in north west England, part I: the relationship with water fluoridation and social deprivation. Br Dent J. 2004;197(7):413-416.

10. Cordray F. Centric relation treatment and articulator mountings inorthodontics. Angle Orthod. 1996;66(2):153-158.

11. Lee R. Jaw movements engraved in solid plastic for articulator con-trols, part I: recording apparatus. J Prosthet Dent. 1969;(22):209-224.

12. Academy of Prosthodontics. Glossary of prosthodontic terms. J Prosthet Dent. 2005;94(7):10-92.

13. Lundeen H. Centric relation records: the effect of muscle action. J Prosthet Dent. 1974;31(3):244-253.

14. Crawford S. Condylar axis position, as determined by the occlusion and measured by the CPI instrument, and signs and symptoms of tem-poromandibular dysfunction. Angle Orthod.1999;69(2):103-116.

15. Hunt K. Bioesthetics: Working with nature to improve function and appearance. Am Acad Cosmet Dent. 1996;12(2):45-50.

16. Hunt, K. Full-mouth rejuvenation using the biologic approach: an 11-year case report follow-up. Contemp Esthet Restor Pract. 2002;6(6):1-6.

17. Lee R. Esthetics and its relationship to function. In: Rufenacht CR, ed. Fundamentals of Esthetics. Chicago: Quintessence; 1990:137-209.

18. Hunt K, Turk M. Correlation of the AACD accreditation criteria and the human biologic mode. J Cosmet Dent. 2005;21(3):120-131.

19. Ash M, Nelson S. Dental Anatomy, Physiology and Occlusion. 8th ed. St Louis, MO: Saunders; 2003.

20. Knight D, Leroux B, Zhu C, Almond J, Ramsay D. A longitudinal study of tooth wear in orthodontically treated patients. Am J Orthod Dentofac Orthop. 1997;112(6):17-18.

21. Masatoshi K, Masanori F. Occlusal factors associated with temporo-mandibular disorder based on a prospective cohort study of young adults. Prosthod Res Pract. 2006;5(2):72-79.

22. Jemt T, Lundquist S, Hedegard B. Group function or canine protection. J Prosthet Dent. 1982;(48):719-724.

23. Straub W. Malfunctions of the tongue. Am J Orthod. 1960;(40):404-420.

24. Kydd W. Maximum forces exerted on the dentition by the perioral and lingual musculature. J Am Dent Assoc. 1957;(55):646-651.


Summary

IntroductionFor the better part of a hundred years, orthodontists have

used Angle’s classification as a means of communication.

When we say “Class I,” orthodontists share the same image,

which is generally a positive concept of how teeth should fit

together. There certainly can be a Class I case with problems,

but Class I is the first major step in describing optimal tooth

relationships. To this day, Angle’s Class I describes a mor-

phologic treatment goal for the orthodontic specialty.

Why do we not have a similar physiologic treatment

goal? Often we talk about “occlusion” in orthodontics, but

it clearly means different things to different people. The term

occlusion lacks the communication value of Class I. A “good

occlusion” is a nebulous term that varies depending on the

person using it. We have a communication problem. We en-

joy general agreement, and hence communication clarity,

regarding morphology, but this is not the case for physiol-

ogy. It would certainly be of value to our patients and the

orthodontic specialty if we had a clear definition of what

constitutes optimal physiology or “good occlusion.”

As in all biologic systems, the structural elements of

the human gnathic system have evolved to perform best un-

der certain conditions of form and function. For example,

there is considerable evidence to support a clear definition

of healthy function for the temporomandibular joint in its

loaded state, such as during a swallow. When loaded, the

condyle should be positioned upward, forward and mid-

sagittally. This definition of optimal joint position is agreed

upon by most authorities1-15 and is well supported by the

literature.16-36 Okeson defines this as the “most musculosk-

eletally stable position of the mandible.”7(112) There also are

data indicating the optimal relationship of the condyle, disc,

and eminence when the mandible is moving into or out of

the loaded position. In this condition, there should be con-

stant contact between the condyle, disc, and eminence.37-40

There are numerous data indicating that neuromuscular

function is highly influenced by tooth contacts and tooth po-

sitions.41-55 For example, as the mandible moves into and out

of intercuspation, guidance from properly positioned ante-

rior teeth aids in separating the posterior teeth. This reduces

the activity of the powerful elevating muscles, which, in turn,

downloads the system while facilitating constant contact be-

tween the condyle, disc, and eminence.39,43,46,47,55-64

Thus, current data point to an optimal physiologic rela-

Angle’s class I has long served the orthodontic specialty as a morphologic

treatment goal and a means of communication. Certainly a physiologic

treatment goal would be of equal value. There are sound data to define and

support such a physiologic goal, which can help orthodontists to better serve

their patients, communicate with other dental professionals, and avoid nu-

merous clinical problems.

andReW GiRaRdoT, ddS, [email protected]■ Graduated from USC School of Dentistry (DDS), 1968■ Graduated from USC School of Dentistry, Dept. of Orthodontics (certificate in orthodontics), 1972■ Part-time Faculty University of Colorado, School of Dentistry, Dept. of Orthodontics■ Cofounder, codirector and faculty, Roth Williams USA, 1997-present

Andrew Girardot, DDS, FACD

Physiologic Treatment Goals in Orthodontics

70 Girardot | Physiologic Treatment Goals in Orthodontics

tionship between the teeth, the joints, and the neuromuscula-

ture. This information provides a physiologic treatment goal

for the orthodontist, a summary of which can be made by an-

alyzing the system in loaded and unloaded conditions. When

loaded, eg, during a swallow, the condyles are fully seated

upward and forward in the fossae, the elevating muscles are

active, and the dentition is in full intercuspation.41,55,62,63,65,66

When unloaded, the condyles remain in firm and constant

contact with the disc and eminence, elevating muscles are in-

active and positioning muscles (eg, lateral pterygoids) are ac-

tive, posterior teeth are out of contact, and the anterior teeth

play a major role in guiding mandibular movements.67-75

Given a reliable perspective of optimal static and dynamic re-

lationships between the teeth, joints, and neuromusculature,

we can consider some additional principles regarding gnathic

function. There are at least three reasons why the intercuspal

position is important. First, the positions and the shapes of

the teeth determine mandibular movements at and near the

intercuspal position.7,50,61,76-100 Second, when the mandible is

brought to full intercuspation in a functionally healthy sys-

tem, the powerful elevating muscles are active and the system

is heavily loaded; the bulk of the resultant force is absorbed

by posterior teeth.32,50-52,101-103 Third, condylar position is de-

termined by the dentition at intercuspation.61,83,104-106

An additional important factor well supported in the lit-

erature is the clinical observation that the neuromusculature

is exquisitely programmed to guide the mandible to the in-

tercuspal position80,85-100,107; the intercuspal position is domi-

nant over condylar position.61,83,103,105,106,108-110 Thus, asking

a patient to “bite down” provides no dependable informa-

tion as to where the condyle is positioned. Moreover, efforts

to identify the seated condylar position through clinical

maneuvers such as manipulating the mandible are not reli-

able.28,111-116 To quote the master clinician Dr. Thomas Basta,

“Don’t believe what you see in the mouth.”2 Thus the value

of using interocclusal devices such as cotton rolls, anterior

jigs, and splints to deprogram the neuromusculature.

If we are to apply these physiologic principles to the

practice of orthodontics, we need additional information

besides that which we have traditionally used; for example,

techniques that record the optimal or “seated” position of

the condyle. Currently there are numerous such techniques

employed in restorative dentistry. Many clinicians use a hard

stop at the incisor midline to separate the posterior teeth,

along with a soft posterior material that can be hardened

thermally or chemically. When the patient bites against the

hard anterior stop and the neuromusculature seats the con-

dyles superioranteriorly, the posterior material is hardened,

and the musculoskeletally stable position of the mandible is

recorded (Figure 1).

The information then must be transferred from the pa-

tient to a device that will allow study and treatment plan-

ning of the gnathic system in three dimensions. Currently,

the articulator appears to be the best tool for this purpose,

although computer-generated three-dimensional technology

may replace the articulator in the near future. Casts mounted

on an articulator provide invaluable physiological informa-

tion for diagnosis and treatment planning. For example,

numerous studies show that there is nearly always vertical

distraction of the condyle when the patient closes to inter-

cuspation.33,113,117-122 It is all but impossible to record, ana-

lyze, and treatment plan this vertical discrepancy without the

use of a device such as an articulator.

Joint images are another tool that can serve orthodon-

tists with regard to physiologic treatment. Tomograms, as

first advocated by Ricketts, have provided an effective way

to study the health of the temporomandibular joint and the

position of the condyle in the fossa.123-125 At present, cone

beam CT is a more effective way to study the temporoman-

dibular joint, as it provides a more-lucid, three-dimensional

view of joint structures.36

There are sound data to support the concept that op-

timal gnathic function can be defined and used as an evi-

dence-based treatment goal. There is little doubt that this

would also aid communication between orthodontists and

other dental professionals. In addition, knowledge of gnathic

physiology is of substantial value to orthodontists in that it

helps them to recognize and avoid myriad problems that oc-

cur in everyday practice. ■

Figure 1 The anterior stop is hard and flat; it separates the posterior teeth to create appropriate space for a recording

medium. The patient is instructed to close firmly, which seats the condyles to the musculoskeletally stable

position of the mandible.


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Summary

IntroductionCentric relation (CR) refers to a physiologic position of the

mandible when the condyles are located in the superoante-

rior position in the articular fossae, fully seated and resting

against the posterior slopes of the articular eminences with

the discs properly interposed.1 It is a reproducible position

that is obtained independent of the occlusion by manipu-

lating the mandible in a purely rotary movement about the

transverse horizontal axis.2

Orthodontic treatment is aimed at achieving static goals

from Andrews’ six keys to normal occlusion and the func-

tional scheme of mutually protected occlusion recommended

by Stuart and Stallard.3,4 In the 1970s, Roth introduced gna-

thological concepts into orthodontic treatment.5,6,7 The goal

of a gnathological approach in orthodontics is to achieve a

functional occlusion, in which the mandible can close into

maximum intercuspation (MI) without deflecting the con-

dyles from CR.8 Dr. Roth believed that a large discrepancy

between MI and CR can lead to breakdown in the stom-

atognathic system, because the condyles are distracted from

the glenoid fossae when the teeth come into occlusion. Signs

and symptoms of occlusal disharmony include temporoman-

dibular joint pain-dysfunction syndrome, occlusal wear and

bruxism, excessive tooth mobility associated with periodon-

tal disease, and movement or relapse of tooth positions.9

Occlusal discrepancies, if associated with joint compression,

The goal of a gnathological approach in orthodontics is to achieve a functional

occlusion, in which the mandible can close into maximum intercuspation (MI) with-

out deflecting the condyles from centric relation (CR). Gnathologic positioners are

used at the end of orthodontic treatment to settle the occlusion while maintaining

MI-CR harmony. The objective of this prospective study was to examine the effect

of gnathologic positioners on MI-CR discrepancy for patients treated with the Roth

gnathological approach.

Methods.The sample consisted of 26 consecutively finished cases in a gnathologically

oriented practice. All cases were treated with a gnathological treatment approach,

using the Roth prescription straight-wire appliance. A gnathologic positioner was

delivered at the time of debonding and was worn for a period of 2 months. Pre- and

postpositioner records were taken. These included a maximum-intercuspation wax

bite; a two-piece Roth power centric CR bite registration; and upper and lower models

mounted using a true hinge transfer and CR bite. The control group consisted of 8

randomly selected finished cases in the orthodontic clinic at the University of Detroit

Mercy and was retained with Hawley retainers. MI-CR discrepancy was measured

with a condylar position Indicator (CPI).

Results. Results indicate a statistically significant improvement in MI-CR discrepancy

in the right horizontal, right vertical, left vertical, and transverse planes after 2 months

of gnathologic positioner wear. The amount of condylar distraction in these 4 mea-

surements showed statistically significant improvement and came within the envelope

of susceptibility.

Conclusions.The positioner and control groups tend to change differently over time

in the vertical and horizontal planes, with the positioner group improving and the

control group getting worse. In the transverse plane, gnathologic positioners improve

the result of orthodontic treatment with respect to condylar axis distraction.

WeSLey m. chianG, ddS, mS■ MA Candidate, Orthodontic Dept., University of Detroit Mercy School of Dentistry

TheodoRe FReeLand, ddS, [email protected]■ Adjunct Professor, Orthodontic Dept., University of Detroit Mercy School of Dentistry ■ Director Roth/Williams USA; ■ Private Practice, Gaylord, MI

RichaRd KuLbeRSh, dmd, mS, PLc■ Program Director, Orthodontic Dept., University of Detroit Mercy School of Dentistry

RichaRd KaczynSKi, bS, mS, Phd■ Statistician, Dept. of Psychiatry, Yale University School of Medicine

Wesley M. Chiang, DDS, MS ■ Theodore Freeland, DDS, MS

■ Richard Kulbersh, DMD, MS, PLC ■ Richard Kaczynski, BS, MS, PhD

Effect of Gnathologic Positioner Wear on Maximum Intercuspation CR Disharmony

76 Chiang, Freeland, et al | Effect of Gnathologic Positioner Wear on Maximum Intercuspation CR Disharmony

can also lead to condylar resorption.10

The clinical acceptable difference between CR and MI

in terms of condylar position is approximately 1.0 mm an-

teroposteriorly, 1.0 mm vertically, and 0.5 mm transverse-

ly.11,12,13,14 The condylar position indicator (CPI) has been

used to accurately record condylar movements.15 A compari-

son between pretreatment and posttreatment records in pa-

tients treated in a gnathologically oriented practice showed a

statistically significant reduction in MI-CR discrepancy in all

3 planes of space.16 The posttreatment records were obtained

before delivery of the gnathologic positioner.

The purpose of this study was to examine the effect of

gnathologic positioners on MI-CR discrepancy for patients

treated with the Roth gnathological approach. The effective-

ness of gnathologic positioners can be determined if there

is a decrease in MI-CR discrepancy following 2 months of

positioner wear.

Research Design and MethodsThe positioner group consisted of 26 consecutively finished

cases in a gnathologically oriented practice (Theodore Free-

land, DDS, MS, Gaylord, Michigan). The sample consisted of

15 males and 11 females. The average age was 15 years and

8 months. All cases were treated with a gnathological treat-

ment approach, using the Roth prescription straight-wire

appliance (GAC, Glendora, California).12 Seven cases were

treated with 4 premolar extractions, while 19 cases were

treated with nonextraction. Four weeks prior to the debond-

ing appointment, prepositioner records were taken (time 1).

The records included upper and lower alginate impressions

in rim lock trays, a true hinge face-bow transfer; an MI wax

bite taken using 10x pink wax (Myoco Industries, Inc, Phila-

delphia, Pennsylvania); and CR bite registration taken using

a two-piece Roth power centric method with Delar blue wax

(Delar Corporation, Lake Oswego, Oregon) (Figure 1).

Figure 1 Two-piece CR bite – anterior segment (A). Two-piece CR bite – posterior and anterior segments (B).

MI bite (C). Two-piece CR and MI bite (D).

The models were poured with a vacuum mixed white stone

(Whip Mix Corporation, Louisville, Kentucky) and mounted

with Whip Mix mounting plaster (Whip Mix corp, Louis-

ville, Kentucky), using a true hinge transfer and CR bite

(Figures 2,3).

Fabrication of Gnathologic PositionerThe gnathologic positioner was fabricated using Oralastic

80 silicone. The true hinge positioner set up is fabricated

according to posterior determinants (angle of the articular

eminence and Bennett side shift). At time 1, a second set of

upper and lower alginate impressions was taken and poured

with white stone. The models were left unmounted, while the

first set of models was mounted using true hinge face-bow

transfer and CR bite. Unmounted models were used to fab-

ricate the gnathologic positioner, using the mounted models

as a reference. Teeth were separated from the models, and

brackets were ground off the teeth. Mandibular teeth were

set to an occlusal plane with proper curve of Spee and curve

of Wilson, and set on arc of closure in CR. The upper teeth

were set to the lower teeth in accordance with ideal overbite/

overjet (OB/OJ).

At the debonding appointment, the braces were removed,

and the gnathologic positioner was delivered. The arc of clo-

Figure 2 True hinge axis.

Figure 3 True hinge mounted models with two-piece CR bite.


sure was first checked in the mounting on the true hinge ar-

ticulator and then checked intraorally with and without the

positioner. The patient was instructed to wear the positioner

full time for the first 3 days (with the exception of eating and

brushing). After the first 3 days, the patient was instructed to

wear the positioner at night, with 4 hours of positioner ex-

ercise during the day. If the positioner should fall out during

the night, the patient was instructed to wear the positioner

for 6 hours during the day.

Positioner Exercise and Wear Protocol The patient was instructed to bite into the positioner just

enough to seat all of the teeth and to fully engage the teeth in

the positioner. The patient was instructed to bite with pres-

sure for about 10 seconds and then to relax for about 15

seconds. The exercise was done in 15-minute intervals, with

15 to 20 minutes of rest in between. For nighttime wear, the

patient was instructed to put the positioner into the mouth

and close the mouth to engage the positioner as much as pos-

sible without putting pressure on the positioner.

The gnathologic positioner was checked for fit and arc

of closure at 1, 2, and 4 weeks after delivery. After 2 months

of positioner wear, postpositioner records were taken (time

2). These consisted of the same records that had been taken

at time 1. Upper splint and lower spring retainers were then

delivered.

The control group consisted of 8 randomly selected

finished cases in the orthodontic clinic at the University of

Detroit Mercy. The control group was not preselected with

regard to MI-CR discrepancy at debond. At the debonding

appointment (time 1), braces were removed and records

were taken. Upper and lower Hawley retainers were deliv-

ered, and the patient was instructed to wear them full time.

After 2 months of Hawley retainer wear, records were taken

again (time 2).

MI-CR discrepancy was measured with a CPI (Panadent

Corporation, Grand Terrace, California) at times 1 and 2 for

both groups (Figure 4,5).

Figure 4 CPI registration with two-piece CR bite (A). CPI registration with MI bite (B). CPI Recording – transverse (C).

CPI Recording – right (D).

Figure 5 Condylar position indicator recording graph (CR – red dot, MI – blue dot).

ResultsThe mean differences between MI and CR of the articula-

tors’ condylar axis position were recorded for the transverse,

and separately for the right and for the left condyles in the

vertical and anteroposterior (A-P) directions. Pre- and post-

treatment measurements of MI-CR discrepancy of the con-

trol and positioner groups are summarized in Table 1.


Table 1 MI-CR Discrepancy Assessment of Control and Positioner Groups.

Table 2 Independent t-test for MI-CR Discrepancies of Control Versus Positioner Group.

Measurements

Control Positioner(n=8) (n=26)

Time 1 Time 2 Time 1 Time 2Mean (mm)

SD (mm) Mean (mm)

SD (mm)

Mean (mm)

SD (mm)

Mean (mm)

Right AP 0.700 0.499 1.225 1.383 1.306 0.897 0.733Right vertical 0.863 0.407 1.238 0.845 1.217 0.969 0.623

Left AP 0.750 0.864 1.625 1.201 0.867 1.010 0.671Left vertical 0.825 0.292 1.062 0.686 1.162 0.794 0.669

Transverse 0.350 0.267 0.288 0.309 1.031 1.106 0.248

t df pRight AP 1.812 32 .079Right vertical 1.000 32 .325Left AP 0.296 32 .769Left vertical 1.164 32 .253Transverse 1.709 32 .097

As the table shows, pretreatment means for the control

group were all within the clinical envelope of ± 1.0 mm for

the A-P and vertical dimensions, and ± 0.5 mm for the trans-

verse. Conversely, 4 out of 5 pretreatment means for the po-

sitioner group were outside this envelope; only the mean left

A-P measurement, at 0.87, was within the clinical envelope.

The control and positioner groups were then assessed by an

independent t-test for any statistically significant pretreat-

ment differences. As shown in Table 2, no differences were

found between the two groups (0.08 < p <0.77).

A paired t-test was used to evaluate change in MI-CR discrep-

ancy from time 1 to time 2 in the positioner group (Table 3).

Table 3 Paired t Tests for MI-CR discrepancies between time 1 and time 2 for the positioner group (df=25).

MI/CR discrepancy

Mean Differences

(mm, absolute values)

Standard Error

t p

Right AP .5731 .189 3.025 .006*Right vertical .5942 .213 2.791 .009*Left AP .1962 .214 0.915 .369Left vertical .4923 .162 3.047 .005*Transverse .7827 .224 3.490 .002*

*Significant at p<.01


For these analyses, the desired significance level of 0.05

was reduced by a factor of 5 (for the 5 variable CPI readings:

right A-P, right vertical, left A-P, left vertical, and transverse)

to control experimentwide alpha and to avoid the risk of

type I errors. Thus a significance level of α = 0.01 was used

for each test of the condylar axis position measurements. The

results indicated statistically significant differences between

time 1 and time 2 for the positioner group in the right A-P (Δ

= 0.57 mm, t = 3.03, p = .006); right vertical (Δ = 0.59 mm,

t = 2.79, p = .009); left vertical (Δ = 0.49 mm, t = 3.05, p =

.005); and transverse (Δ = 0.78 mm, t = 3.49, p = .002) mea-

surements. There was no statistically significant difference in

the magnitude of condylar distraction in the left condyle in

the A-P direction (Δ = 0.20 mm, t = 0.92, N.S.).

Mixed-design analyses of variance compared the po-

sitioner and control groups’ change in MI-CR discrepancy

over time (Table 4).

Table 4 Mixed Design Analysis of Variance for MI-CR Discrepancies from time 1 to time 2 between Control Versus Positioner Group.

Using the adjusted significance level described above

(α = 0.01), these comparisons between the 2 groups showed

no statistically significant differences in any of the 5 CPI

measurements. However, 4 of the 5 dimensions fell below

the traditional α = 0.05 level. Graphical representations of

the change in MI-CR discrepancy over time for the position-

er and control groups are shown in Figures 6 through 10.

Figure 6 Right horizontal MI/CR discrepancy. Figure 7 Right vertical MI/CR discrepancy.

Effect F* pRight AP Time 0.012 .915

Time x group 6.096 .019Right vertical Time 0.266 .609

Time x group 5.203 .029Left AP Time 2.431 .129

Time x group 6.053 .019Left vertical Time 0.599 .445.

Time x group 4.917 034Transverse Time 4.102 .051

Time x group 2.978 .094

* df for all tests are 1, 32.


Figure 9 Left vertical MI/CR discrepancy.

Figure 10 Transverse MI/CR discrepancy.

DiscussionResults of the present study indicate a statistically signifi-

cant improvement in MI-CR discrepancy in the right hori-

zontal, right vertical, left vertical, and transverse planes

with 2 months of gnathologic positioner wear. The condy-

lar axis distraction differences in the left horizontal planes

were not statistically significantly different. Before positioner

wear, the mean right horizontal, right vertical, left vertical,

and transverse measurements were 1.306 mm, 1.217 mm,

1.162 mm, and 1.031 mm respectively, and fell outside the

± 1.0 mm vertical and horizontal as well as the ± 0.5 mm

transverse distraction envelope proposed by Crawford, Utt

et al, and Slavicek.12,13,14 Following 2 months of positioner

wear, the amount of condylar distraction in these 4 mea-

surements showed statistically significant improvement and

came within the distraction envelope. Before positioner wear,

3 patients (11.5%) had MI-CR discrepancy that fell within

the envelope of susceptibility in all 5 of the measurements

examined, while 11 patients had all 5 measurements within

the envelope after positioner wear (42.3%). Reducing MI-

CR discrepancies is an important treatment goal in the gna-

thological philosophy, and the use of gnathologic positioner

is essential to achieving this goal.

Although these changes were nonsignificant when com-

pared to change in the control group, the level of signifi-

cance in the right horizontal, right vertical, and left vertical

planes was very close to the significance level of 0.01 used

for this study, and below the more common 0.05 level of

significance. Figures 6, 7 and 9 show a similar pattern with

reduction in MI-CR discrepancy over time with positioner

wear, while the group with the Hawley retainers shows an

increase in MI-CR discrepancy. This trend is observed in 3 of

the 5 measurements studied (right horizontal, right vertical,

and left vertical planes). The positioner and control groups

tend to change differently over time in the vertical and hori-

zontal planes, with the positioner group improving and the

control group getting worse. This is consistent with Roth’s

claim that general retention protocols with Hawley-type ap-

pliances following orthodontic therapy will tend to make

MI-CR discrepancy worse, while gnathologic positioners

will improve MI-CR discrepancy. Interestingly enough, all

mean vertical and horizontal CPI measurements for the con-

trol group started within the distraction envelope of ± 1.0

mm and finished outside the envelope following 2 months of

Hawley retainer wear.

The small sample size of the control group is a limitation

of this study. A larger sample size would eliminate type II er-

ror and might show a statistically significant difference in the

change in MI-CR discrepancy over time between the control

and the positioner group. However, the p-values are below

Figure 8 Left horizontal MI/CR discrepancy.


the .05 level of significance in the right horizontal, right ver-

tical, and left vertical planes. Furthermore, the MI-CR pat-

tern is observed, suggesting that this is not a purely random

phenomenon. Since the control group was small, there is the

possibility of an underpowered study.

In the transverse plane, there appears to be no difference

between the 2 groups over time. A condylar axis distraction

in the transverse plane is more sensitive to clinical problems

than a condylar axis distraction in the horizontal and vertical

planes.17,18,19 It appears that gnathologic positioners improve

the result of orthodontic treatment with respect to condylar

axis distraction.

ConclusionResults of the present study indicate a statistically significant

improvement in MI-CR discrepancy in the right horizon-

tal, right vertical, left vertical, and transverse planes with 2

months of gnathologic positioner wear. The amount of con-

dylar distraction in these 4 measurements showed statisti-

cally significant improvement and came within the envelope

of susceptibility. The positioner and control groups tend to

change differently over time in the vertical and horizontal

planes, with the positioner group improving and the control

group getting worse. In the transverse plane, gnathologic po-

sitioners improve the result of orthodontic treatment with

respect to condylar axis distraction. ■

References1. Okeson JP. Management of Temporomandibular Disorders and Oc-clusion. 3rd ed. St Louis, MO: Mosby; 1998:109-125.

2. Schmitt ME, Kulbersh R, Freeland T, et al. Reproducibility of the Roth power centric in determining centric relation. Semin in Orthod. 2003;9(2):102-108.

3. Andrews LF. The six keys to normal occlusion. Am J Orthod. 1972;(62):196-309.

4. Stuart CE. Good occlusion for natural teeth. J Prosthet Dent. 1964;(14):716-724.

5. Roth RH. Temporomandibular pain dysfunction and occlusal rela-tionships. Angle Orthod. 1973;(43):136-153.

6. Roth RH. Treatment mechanics for the straight wire appliance. In: Graber TM, Swain BH, eds. Orthodontics: Current Principles and Techniques. St Louis, MO: Mosby; 1985:665-716.

7. Roth RH. Occlusion and condylar position. Am J Orthod Dentofac Orthop. 1995;(107):315-318.

8. Pangrazio-Kulbersh V, Poggio V, Kulbersh R, et al. Condylar distrac-tion effects of two-phase functional appliance/edgewise therapy versus one-phase Gnathologically based edgewise therapy. Semin in Orthod. 2003;9(2):128-139.

9. Roth, RH. The maintenance system and occlusal dynamics. Dent Clin North AM 1976;20:761-788

10. Arnett GW, Milam SB, Gottesman L. Progressive mandibular retrusion-idiopathic condylar resorption, part II. Am J Orthod. 1996;(110):117-127.

11. Roth RH. Functional occlusion for the orthodontist, part I. J Clin Orthod. 1981;(15):32-51.

12. Crawford SD. Condylar axis position, as determined by the occlu-sion and measured by the CPI instrument, and signs and symptoms of temporomandibular dysfunction. Angle Orthod. 1999;(69):103-116.

13. Utt TW, Meyers CE Jr, Wierzba TF, Hondrum SO. A three-dimen-sional comparison of condylar position changes between centric rela-tion and centric occlusion using the mandibular position indicator. Am J Orthod Dentofac Orthop. 1995;(107):298-308.

14. Slavicek R. Interviews on clinical and instrumental functional analysis for diagnosis and treatment planning, part I. J Clin Orthod. 1988;(22):358-370.

15. Lavine D, Kulbersh R, Bonner P, Pink FE. Reproducibility of the condylar position indicator. Semin in Orthod. 2003;9(2):96-101.

16. Klar NA, Kulbersh R, Freeland T, et al. Maximum intercuspation-centric relation disharmony in 200 consecutively finished cases in a gnathologically oriented practice. Semin in Orthod. 2003;9(2):109-116.

17. Kulbersh R, Dhutia M, Navarro M, et al. Condylar distraction effects of standard edgewise therapy versus gnathologically based edgewise therapy. Semin in Orthod. 2003;9(2):117-127.

18. Freeland T, Kulbersh R. Orthodontic therapy using the Roth gna-thologic approach. Semin in Orthod. 2003;9(2):140-152.

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82 Notes

Notes


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