PROFILE

Dr. Lloyd Miller

Current Occupation Private Practice, Weston, MA

Education Tufts University School of Dental Medicine, Boston, BS. MA, DMD (magna cum laude)

hffilistions Clinical Professor, Tufts University School of Dental Medicine, Graduate and Postgraduate Prosthodontics reaching Undergraduate Prosthodontics ’resident and Owner, Gnathos Dental -aboratory, private laboratory and *esearch facility !ditorial Board Member for the Journal 3f Esthetic Dentistry

:.llowshlpr ’ast N.E. Section Chairman, American :allege of Dentists (FACD) nternational College of Dentists (FICD) jreater New York Academy of ’rosthodontics 4merican Academy of Dental Science

profesdonal Memberships ’ast President, Omnicron Kappa Upsilon ’ast President, American Academy of :rown and Bridge Prosthodontics ’ast President, I.R. Hardy Conference ’ast-President, American Academy of isthetic Dentistry

IonordAwardr -bird I.R. Hardy Award -ufts University Dental Alumni Award in isthetics ielected by Bachrach Photographers for Iistinguished Contribution to Dentistry Iistinguished Lecturer Award, American :allege of Prosthodontics, 1997 Iistinguished Service Award, Tufts Jniversity, 1999

’ubliutions :ontributing author for reputable journals uch as the Journal of the American lental Association, Quintessence, and lournal of Esthetic Dentistry

losearch Projests )ouble castings in ceramo-metal :ontamination of ceramo-metal ipectrophotometric studies and iorcelain shade alteration inathos Dental Color System-inventor If variable thickness shade tab former latent, 4, 617, 159

Masters of Esthetic Dentistry

SYMBIOSIS OF ESTHETICS AND OCCLUSION: Thoughts and Opinions of a Master of Esthetic Dentistry

Lloyd Miller, BS, DMD

rom the literature crossing my F desk and the many lectures devoted to esthetics, it is apparent that there is a tremendous promo- tion of artificial standards of beauty for teeth. Many of these attractive smiles enhance the media appear- ance of brightness and symmetry without evaluation of force on teeth or joints. This exceptional interest of patients in their image presents a pregnant opportunity to educate them about total oral health with longevity by controlling force on teeth, muscles, and joints, as well as other oral health issues.

What I also observe is a failure to fully evaluate, diagnose, and treat- ment plan the synergism of anterior esthetics, anterior guidance, and posterior teeth as part of strategic plan for long-term health care. Patients should have a clear idea that our profession is responsible for comfort, stability, and function of the temporomandibular joints as well as the muscles of mastication and the teeth. The title of “Smile DOC’’ then broadens to include management of force on the joints and the teeth as well as promotion of balance and efficiency in the masticatory muscles.

I would like all of our profession to individually address the standard of care (SOC) we offer to our patients. For my own use, I divide SOC into two levels:

Level I: Minimum care to correct caries, infection, disease, inflamma- tion, and pain. Adequate function is determined by the patient and third party systems. Longevity is not required.

Level 11: Optimal care to provide maximum longevity of the dentition with freedom from infection, dis- ease, pain, and tooth loss. Comfort, function, and esthetics are issues between the patient and the dentist. Evaluation, diagnosis, and treatment planning with respect to joints, muscles, and teeth are provided for strategic long-term care.

Let us explore the symbiosis of esthetics and occlusion. In particu- lar I wish to examine management of force on posterior teeth or implants.

I sometimes think many of our problems begin with the fact that there are clever dentists who “fly by the seat of their pants”

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Figure 1. A, Pretreatment young patient. B, Post-treatment with porcelain laminates emphasizing youthful form and composition. (Ceramics by Yasuhiko Kawabe)

(i.e., without careful evaluation and planning). They seem to get by. Some locate and pay superb laboratory technicians to rescue them from inadequate preparation. Their patients may look beautiful, praise their dentists as the world’s best, and pay generous fees-as much as

the careful, responsible dentist receives, who applies himself to the task of optimal esthetic and health for the entire masticatory system. There is a certain smugness, arro- gance, or self-applause for success- fully (apparently) solving (fixing) a dental problem without a flight

Figure 2. A, Mature restoration with porcelain laminates on four incisors. Note ageing effects. B, Retracted view of maxil- lary restorations. C, Completed lower incisor porcelain lami- nates to emphasize mature teeth. (Ceramics by Yasuhiko Kawabe)

plan. It’s infectious and intoxicating for the apparent genius who pulls it off. Given a choice for your own mouth, which would you choose, a strategic plan for longevity, or “with my experience and skill who needs all that preliminary stuff?” The demise of the use of the face bow

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and of the semiadjustable articulator are examples of this attitude.

A N T E R I O R G U I D A N C E

The Pilot of Occlusion and the Mother of Esthetics Anterior teeth are the vital link in force management and stability of the jaw joints and posterior teeth. Within the ability of the dentist potentially to alter and control are five important features of anterior teeth: esthetics, muscle activity and force management, posterior dis- clusion, envelope of function, and incisal edge position.

Esthetics. A most obvious role of the anterior teeth in the contempo- rary world is esthetics. Teeth play a vital part in projecting age, vitality, sexual attractiveness, and self- esteem (Figures 1 and 2). Bondable materials offer esthetic alterations to the teeth for almost all patients. The many variations in direct and indirect procedures allow dentists of many skill levels to offer this cos- metic service. Cosmetic improve- ments to maxillary anterior teeth frequently alter tooth length, incisal edge position, and anterior guidance. It is prudent to evaluate lip support, phonation, envelope of function, muscle activity, condyle position in intercuspal position, and forces on posterior teeth before making irre- versible and fixed changes to ante- rior teeth.

Alterations in anterior guidance necessitate occlusal screening or evaluation. Force management is part of occlusal screening and requires mounting accurate study casts in centric relation on a suit- able semiadjustable articulator. The upper cast is positioned by means of a face bow that relates the upper cast to the face (esthetics) and the hinge axis of the condyle and disk assembly in its uppermost medial position. With the condyles seated in their most stable position, defec- tive occlusal contacts can be ana- lyzed, and these destructive forces related to tooth wear, mobility, drifting, and other well-recognized signs and symptoms of dangerous force (Figure 3 ) .

Muscle Activity and Force Manage- ment. The anterior teeth protect the posterior teeth in eccentric movements by depressing the activ- ity of the elevator muscles during posterior disclusion. A strategic article by D’Amico offers the premise that where the contact of the canines moves from the inter- cuspal position to lateral or forward contact there is a reflexive reduction in tension of the temporal and mas- seter muscles with concomitant reduction in force. Thus was born the canine-protection theory of occlusion. Further studies by others reached the conclusion that elevator muscle tension is reduced with pos- terior disclusion.

The study of Williamson and Lindquist supports this concept.2 Two occlusal schemes were devel- oped with maxillary acrylic resin splints, one produced posterior dis- clusion in all excursive movements with anterior guidance. Then the anterior guidance was reduced until total mandibular tooth contact with the splint was available in all eccen- tric guidance. Results show appre- ciable reduced elevator muscle activity with posterior disclusion. When the anterior guidance was eliminated, there was no reduction in muscle activity. The authors con- clude that it is not canine contact but the absence of posterior con- tacts that breaks the tension.

The goal of posterior disclusion is to reduce elevator muscle tension, eliminate lateral forces on posterior teeth, and allow the condyles to seek normal physiologic positions by eliminating deflective tooth con- tacts. Kerstein’s studies indicate a lengthy disclusion time may be a diagnostic factor for chronic myofacial pain-dysfunction syn- d r ~ m e . ~ Reduction in disclusion time results in significant decrease of elevator muscle activity.

Another example of force manage- ment is the study by Belser and Hannar~ ,~ in which patients were selected whose natural teeth anterior guidance was worn, probably as a result of bruxism, so that group

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Figure 3. A, A postorthodontic view of a young female who requested replacement o f maxillary incisor restorations, to improve color, proportions, and length. B, Occlusal screening with diagnostic casts mounted. C, Defective occlusal contacts on second molars in centric relation show results of excessive force (wear facets). D, Occlusal equilibration on mounted casts show excessive adjustment to return to original uertical dimension. This was unacceptable to the patient. E , Graphic representation of condyles in stable position (CR) but excess force fulcrum on second last molars. F, esthetic temporaries using maximal intercuspal position. Cost: benefit of C R position and patient refusal required restoration in this position. Patient was sup- ported with an occlusal appliance.

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function on the working side and some nonworking side contacts were present. When the working side canine was altered to produce pos- terior disclusion “significant reduc- tion of muscle activity” was evident. It might be postulated from these studies that those patients in whom anterior guidance is reduced until posterior contact occurs during eccentric movements are able to cre- ate more force on the anterior teeth.

What standard of care is this if we ignore posterior tooth contact while focusing only on anterior cos- metics? Will we blame damage to restorations or teeth on the dental manufacturer, patient, or labora- tory technician? We cannot ignore such studies.

Posterior Disclusion. The absence of posterior tooth contact in eccen- tric movements is the result of the combination of anterior guidance and the influence of the position of the condyle-disk assembly on the eminentia (Figure 4). The space developed between the upper and lower posterior teeth plays a signifi- cant role in muscle tension (force management) and destructive tooth contacts. It may be argued that con- tacting incline planes enhance chewing efficiency or that they are necessary for programming maxi- mum intercuspation position. How- ever, when inclined planes do con- tact, parafunctional habits can exert strenuous forces on posterior teeth,

resulting in excessive wear, drifting, splitting, and mobility problems. When the adaptability of the patient is exceeded, there is a high potential for disruption of the condyle-disk assembly as well as triggering mus- cle imbalance. A strategic plan for longevity and health includes evalu- ation of the presence or absence of posterior eccentric tooth contacts as well as defective contacts in centric relation and their effect on muscles, joints, and teeth. As a minimum, the laboratory requires the follow- ing specific information from the dentist to produce predictable pos- terior disclusion in all mandibular eccentric positions:

1. Face bow registration. 2. Centric relation recording. 3. Protrusive check bite to set the

condylar path angle. (A panto- graphic tracing for a fully

adjustable articulator provides more accurate and complete information for condylar paths.)

4. Diagnostic casts that demonstrate anterior guidance.

5. Anterior tooth length and incisal edge position.

6. Anterior guide table adjustment, preferably a custom guide table that accurately reproduces a comfortable working anterior guidance.

Envelope of Function. Within the border limits of mandibular move- ment lies the envelope of function. This is the three-dimensional descrip- tion of the space occupied by the mandibular teeth during normal functional activity. It varies and is unique for each individual. The work of Gibbs et a1 exemplifies the many studies in this area.5 Gibbs and Lundeen verify the variability from

Figure 4. Graphic representation of posterior disclusion that permits free movement of the condyle-disk assembly and anterior teeth.

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Figure 5. Graphic representation depicting envelope of function. A, Frontal view; B, sagittal view. I = good occlusion; 11 = bruxer; I l l = malocclusion. Note geometry o f the apex. (Reprinted with

patient to patient (Figure 5).6 Extremes in horizontal and vertical limits may be observed. Some people chew and brux horizontally (like cows) and others chew vertically (like bears). Tooth contact during this individual activity determines

the three-dimensional contact of the incisal edges of mandibular anterior teeth with the articulating surfaces of the maxillary anterior teeth. It can be observed that shallowing the anterior guidance falls within the adaptability of many patients. But

this can lead to posterior tooth con- flict unless designed otherwise. Steepening the anterior guidance is less predictable and may lead to excessive force on anterior teeth with concomitant wear, fracture, and discomfort (Figure 6).

Figure 6. Envelope of function: sagittal view and incisal edge position. Altering the envelope of function from, for example, form A to form B, may lead to serious restriction o f mandibular movement. (Reprinted with permission. ’)

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Figure 7. Custom incisal guide table generated from diagnos- tic casts. This provides the best possible three-dimensional representation of anterior guidance and envelope o f function.

The arc of closure to centric rela- tion in the terminal hinge position does not include all the parameters of the envelope of function. The best means of transferring anterior guidance and envelope of function to an articulator is to mount casts of successful anterior guidance and envelope of function generated in the mouth. A face bow with a third reference point locates these diag- nostic casts the same as the planned master casts in relation to the face, condyles, condylar angle, and the bench top. These diagnostic casts then are used to generate an articu- lator custom anterior guide table in resin, which faithfully duplicates the many paths traveled by the mandibular incisal edges against the maxillary teeth (Figures 7, 8,

mechanical metal table, or proceed- ing with no direction at all.

Another feature of the envelope of function and anterior guidance as expressed by the custom anterior guide table is to incorporate long centric. Starting from rest position the mandible moves in an arc to reach the intercuspal position. To avoid interference with the maxil- lary teeth, the mandibular teeth require allowance for this deviation from the terminal hinge position arc of closure. The custom anterior guide table easily incorporates this individual feature. Long centric is a small dimension, usually less than 0.5 mm.7 It is also possible to grind in new crowns in the mouth to incorporate this necessary feature. Cheaply made crowns are easy to

and 9 ) . This is a better plan than leaving it to the imagination of the laboratory technician or to a

Figure 8. Graphic representation o f long centric, which permits the mandible to reach maximum closure without anterior interference.

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Figure 9. Lingual view of long centric compared to centric relation and border limits.

grind in the mouth with little remorse-not so with expensive artistic crowns. The patient may adapt, or push the maxillary crowns out of the way, or demon- strate excess wear or tooth fracture. I have seen them all in my practice.

Incisal Edge Position. Patients fre- quently have anterior teeth changed for cosmetic purposes only. The incisal edge is a component of ante- rior guidance and as such may affect posterior teeth. Successful treatments also require close atten- tion to lower lip sensitivity to tooth

length and horizontal position (Figure 10). This is closely allied to some phonetic problems. Failure to evaluate and address lower lip sen- sitivity easily may lead to patient rejection of the finest appearing anterior restorations. Incisal edge position also can be shifted by

Figure 10. A, Provisional temporaries with 5.0-mm horizontal overjet. B, Lower markings show correct position of incisal edge position on wetldry line, compared to excess overjet in A.

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Figure 11 . A, Pretreatment photograph showing reverse smile curve. Occlusal screening indicated deflective occlusal contacts because of inadequate anterior guidance. B, Diagnostic wax- up coupled with occlusal equilibration to produce posterior disclusion. Esthetic needs apparently incorporated as an esthetic-function combination. C, Provisional temporaries, which meet the needs of posterior disclusion but are too long for the patient, especially the canines. Solution required shortening the temporary and building-up the lower canines to correct functional needs.

repositioning the mandible posteri- orly as in occlusal equilibration or when increasing the vertical dimen- sion. Both procedures may position the mandible distally with the upper

incisors now touching the lower lip in a more anterior position. Educat- ing the patient before such treat- ments is essential to avoid patient distrust.

However, when the length of maxil- lary teeth is increased or restora- tions are too thick labially, the patient is likely to blame the dentist for lower lip discomfort. Computer

Figure 12. A, Pretreatment photograph of abused dentition demonstrating excessive wear to anterior guidance and poor esthetics. After thorough occlusal screening, diagnosis, and treatment planning, the patient was fitted with posterior provisionals and mock bonding of the incisors. B, Provisional stage with recreated anterior guidance, centric relation treatment position, posterior disclusion, and new esthetic evaluation.

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Figure 13. A, Pretreatment photograph of young female requiring esthetic correction. B, Following occlusal equitibration to achieve a treatment position of centric relation, a single anterior tooth is prepared for porcelain laminate. An impression now preserves an accurate incisal edge position before the remaining teeth are prepared.

imaging has little value here. When such changes are planned, interim restorations are indicated, to evalu- ate the planned changes in function and esthetics. Esthetic and func- tional analysis is achieved with full crowns by carefully designed provi- sional temporaries (Figure 1 1 ) . Mock bonding on natural teeth provides an excellent means for

patient and dentist to evaluate the proposed final design (Figure 12). Having modified the interim restoration to satisfy esthetic func- tional, phonation, and comfort needs a dentist now has a three- dimensional blue print for the final restoration. Transferring this infor- mation to an articulator remains a primary task for the dentist. In its

simplest form, a study cast of the interim restorations is transferred to the articulator with a face bow and occlusal registration the same as will be used for the master model. A silicon key of the temporaries is applied to the master cast and pro- jects the incisal edge position from the study cast. To go one step fur- ther, the dentist should prepare one

Figure 14. A, Finished porcelain laminate demonstrating a young dentition with excellent tissue health. B, In black and white, it is clearly evident that form, function, and esthetics meet in harmony. (Ceramics by Yasuhiko Kawabe.)

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tooth completely and make an impression (Figure 13). This will precisely locate the thickness and the incisal edge position for the technician. Dawson recommends preparing every other tooth.8 Is there a better way? I don’t know of one. Wouldn’t it be great if we planned for form, function, and esthetics (Figure 14).

CONCLUSION

Five of the most common areas of interaction between the esthetic zone (anterior teeth), posterior teeth, and the rest of the mastica- tory system of muscles and joints have been discussed. The highest standard of care incorporates these features in a strategic plan for long- term oral health. The symbiosis of

esthetics and occlusion precludes treating anterior teeth as cosmetic challenges alone.

PERSONAL A C K N O W L E D G M E N T

I am most appreciative of the superb skills, support, and loyalty of the Cenathos Dental Laboratory.

REFERENCES 1. D’Amico A. The canine teeth. Normal

functional relation of the natural teeth of man. Monograph. J S C Dent Assoc 1958; 2663.

2. Williamson EH, Lundquist DO. Anterior guidance: its effect on electromyographic activity of the temporal and masseter mus- cles. J Prosthet Dent 1983; 49:81&823.

3. Kerstein RB. Disclusion time measurement studies: a comparison of disclusion time between chronic myofacial pain dysfunc- tion patients and nonpatients: a popula- tion analysis. J Prosthet Dent 1994; 72:473-480.

4. Belser VC, Hannan AG. The influence of altered working-side occlusal guidance on masticatory muscles and related jaw move- ment. J Prosthet Dent 1985; 53:406413.

5. Gibbs CH, Messerman T, Reswick JB, et al. Functional movements of the mandible. J Prosthet Dent 1971; 26:601-610.

6. Gibbs CH, Lundeen HC. Advances in occlusion. Boston: John Wright PSG Inc., 1982.

7. Dawson PE. The concept of complete dentistry. Seminar 1. St. Petersburg, FL, January 22-23,1994.

8. Dawson PE. Evaluation, diagnosis, and treatment of occlusal problems. 2nd Ed. Reinhardt RW. Restoring Upper Anterior Teeth. St. Louis: CV Mosby, 1989:334-335.

Reprint requests: Dr. Lloyd Miller, 56 Colpitts Road, Weston. MA 024930 81999 B.C. Decker Inc.

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