As evidence to our profession’s desireto improve dental health and deliv-ery of care, we have seen many

advances in the art and science of dentistry.Even during my relatively short 20 years ofpractice,  I have adopted many new materi-als and techniques to offer my patients thebest possible care. My observations, afteryears of clinical microscope dentistry andstudy of past research, have led me to con-clude that despite our best intentions, weare falling short. Some of our techniques areincompatible with our most common pro-cedures leading to avoidable failures. Weneed to reassess and recalibrate ourendodontic and restorative techniques tobest suit the way that we practice today. Atthe same time, we need to preserve essentialtooth structure to routinely achieve a 50-year, not a 5-year, successful outcome. Inthis article, I will address how restorativedentists can reclaim endodontics and rein-vent direct restorative techniques for clini-cal success.

The shapes we cut, both endodonticallyand restoratively, are a very big deal.Interestingly, in endodontics, we haveembraced a radical change in the shapesthat we cut for root shaping (big versussmall) in spite of the outcome studies thatdo not validate this aggressive removal ofprecious dentin. Meanwhile, in restorativedentistry, we cling to modified G. V. Blackpreparations, namely retentive Class I andClass II preparations that do not serve theclinician, composites, or the tooth. As I lookto the future, I see a daunting task in revers-ing the massive inertia of the dental indus-try that has created materials, instruments,and techniques to serve 2 perverse masters.Let’s begin with endodontics.

PART I: RECLAIMING ENDODONTICS Endodontic Design

Endodontic design refers to accesspreparation and canal shaping. Fordecades restorative dentists havedeferred to endodontists to determine endo -dontic design. It is imperative that restora-tive dentists reclaim endodontic design andwork in concert with endodontists (Figure1). We need to move away from round buraccess preparations which tend towardsparallel-sided access, as is so frequentlyshown in texts. This invariably results ingouging of the all-important peri-cervicaldentin (PCD) (Figure 2). The PCD is the zoneof dentin extending 4 mm coronal to 4 mmapical of the crestal bone. Round-bur accessalso makes discovery and negotiation of cal-cified canal systems difficult. In contrast,when an infinity edge cavosurface marginmerges with a conical access, a whisper ofpulp can be more easily discovered with thefile tip; the new Micro-Endo Access Burs (SSWhite), available in November, do just that.These new burs have a polished carbide con-

ical shape that is self-centering to create abeautifully smoothed dentinal surface thatsimplifies finding calcified canals by virtueof these 3 important attributes (Figures 3and 4). (David: Are the previous sentencesOK, as edited? DCA)

When we take a round bur and rum-mage around the calcified tooth, the tip ofthe round bur typically becomes slightlymisdirected. When the file is inserted, itclunks into the bottom of the well. We con-tinue to drill deeper and go back and forth,burrowing and then clunking files into thefruitless bottom, when in reality the tinytrace of pulp is along the lateral wall. Withconical access, the tip of the file can trace upand down the converging walls of the coneof dentin and the file is nicely directed intothe pulp chamber, even when the tip of the

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DENTISTRYTODAY.COM • OCTOBER 2010

Figure 1. A new model for incisor access is

depicted, along with the new Micro-Endo

access bur. Note that the access has been

moved away from the cingulum and toward the

incisal edge.

David J. ClarkDDS

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This, and all future articles that are presentedin multiple parts, will now be available to ourreaders for review in their entirety at our Website, dentistrytoday.com. This is being done tohelp those readers who may have missed a portion of any multiple-part article, and willalso facilitate the ability to review a completearticle in its entirety for others.

Figure 3. Prototype Micro-Endo

Access bur kit by SS White with

conical carbide burs in 27 and 34

mm lengths.

Figure 4. Comparison of the Micro-Endo burs (which are coni-

cal carbides) with corresponding round bur. The tip size is less

than half that of the corresponding round bur.

Figure 2. Classic iatro-

genic gouging typical

of round-bur access

combined with cingu-

lum access likely com-

pounded by insufficient

magnification.

3

cone is off-center. I have been pleas-antly surprised to find pulp very earlyon, often far coronally to where thepulp begins to appear on the radi-ograph (Figure 5).

Big Endodontic Root Shapes: A Step Backward?

The big, aggressive canal-flaring partyis officially over. The movement awayfrom conservative endodontic shap-ing to large, flared endodontic shapeswas well intentioned. At BostonUniversity, Dr. Herb Schilder’s visionof modern endodontics was the pur-suit of 3-dimensional (3-D) obturationof complex canal systems; this wasdone in the hope that the warm com-paction of gutta-percha and sealer outthe lateral and apical extents of thesystem would create better outcomes(Figure 6). Well, these hollowed teethare much more prone to fracture.1,2

Whereas endodontic design that isbiomimetic3 and extremely conserva-tive would probably not weaken thetooth. This is because the dentin inthe endodontically treated tooth isnot more brittle or with a lower mois-ture content than a natural untreatedtooth.4-6 We may have created a gen-eration of dentists and patients whohave seen so many endodontically-treated teeth fracture that they nowunderstandably view endodonticallytreated teeth as “weak.” Besides frac-turing, one of the last nails in the “bigshapes” coffin is the recent study pub-lished in the Journal of Endodontics.7 Itsuggests that aggressive canal shapingand 3-D obturation may not result in abetter seal.7 In this study, 493 humanendodontically treated teeth wereextracted and examined for histo -pathologic and histobacteriologic sta-tus of tissue in lateral canals. Theyfound that “lateral canals thatappeared radiographically filled werenot obturated,” and “Overall the beliefthat lateral canals (and apical ramifi-cations) must be injected with fillingmaterial was not supported by litera-ture review or by our histopathologicobservations.”8 In other words, we

can’t predictably fill all of the lateralcanals, even when the radiographshows all of those “sexy puffs of seal-er.” In the cases where the lateralcanals appeared radiographically ob -turated, the histologic serial sectionsshowed the lateral canals to be morelike a garage sale of bacteria, chaoticchunks of filling material, inflamma-tory cells, etc. We should default backto small endodontic design because:(1) the tooth will be stronger and (2)there is insufficient evidence that bigshapes provide a better seal and thusfewer endodontic failures.

What dismays endodontists is theconfusion between small and sloppy.Endodontists tend to see failing caseswith “small shapes” like this centralincisor case (Figure 7a) and under-standably make the link betweensmall shapes, sloppy work, and fail-ure. This does not necessarily follow.To demonstrate the shape Dr. Khad -emi and I are recommending, the casein Figure 7a with a lateral lesion isfirst delicately shaped and obturatedto the apices with calcium hydroxide(Figure 7b), and carefully sealed withno cotton pellet and a combination ofCavit (3M ESPE), and flowable com-posite directly over the CaOH (UltraCal [Ultradent Products], Cavit, andFiltek Supreme Ultra flowable com-posite [3M ESPE]). The canal system isallowed to disinfect and begin to healfor 8 weeks. Although the lateralcanal was not radiographically obtu-rated, the lateral lesion has healednicely. (Figures 7c and 7d) In contrast,another case (Figures 8a to 8c) had abeautiful radiographic fill of the later-al canal and yet is not healing to mysatisfaction. Both of these cases weretreated by me with careful calciumhydroxide therapy before the obtura-tion appointment.

So if Mainstream Dentistry Cannot Adequately Seal LateralCanals, Why Do We Not See More

Endodontic Failures?Case spectrum is important. Somegifted and committed microdentistsexist who may actually succeed insealing the majority of lateral canalsand apical ramifications. They accom-

plish this by committing additionaltime, massaging precurved hand filesinto multiple orifices, and so on.While these procedural nuances maybe important in a small spectrum ofcases, it’s not reasonable to expect thisin mainstream dentistry treating vitalor recently necrotic cases. It’s proba-bly not even necessary (in a vital case).The good news is that the above men-tioned study showed that, for vital

(nonlesion, noninfected) cases, thehistology looked a lot like a deep pulpcap; with happy pulp and periodontaltissue nestled next to gutta-percha. Inother words, the lateral canals andapical ramifications were filled withhealthy tissue supported by the vascu-lar supply of the surrounding bone.Sealer may not be all that important.Go figure!

Uniform Wall ThicknessUniform wall thickness of the resid-ual root dentin is a casualty of theaggressive use of Gates Glidden burs,rotary files, and old school straight-line access. In Figure 9 we see a sec-tioned immature root that has a largepulp space but naturally absolute uni-form wall thickness. Studies need tobe performed on the merits of thisattribute. Restorative dentists do nottypically see root fractures of thesenaturally “hollow” teeth in their ado-lescent patients. We also intuitivelyunderstand that a thin area of dentinis a liability in so many ways. Thephotoelastic studies of stressed root-canal-treated roots definitely showthat uneven flexure occurs in endo -dontically-treated roots when a round

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Figure 5. This series of radiographs demonstrates how a conical carbide bur assists the clinician

in finding calcified canal systems in a less traumatic fashion. The bur can also be used with radi-

ographs to assess both location and direction of access.

Figure 6. This narrow endodontic shape of the

silver cone (right) is a 50-year success, a far

cry from the mutilated shapes that are now in

vogue with some clinicians (left).

Figure 7a. Preoperative view showing a large lateral lesion. Figure 7b. Calcium hydroxide place-

ment with exquisite seal and no cotton pellet. Figure 7c. Postoperative radiograph suggests that

the lateral canal was not radiographically obturated. Figure 7d. In spite of the lack of a radi-

ographically filled lateral canal, the lateral lesion appears completely healed at one-year follow up.

Note how the case was kept about the same shape as the preoperative shape (not significantly

enlarged).

Figures 8a to 8c. Pre-, postoperative, and one-year follow-up x-rays show that in spite of a radiograph-

ically obturated lateral canal, the lateral lesion is not healing. Extraction was originally offered as an

alternative to endodontic therapy but the patient opted to try to save the tooth.

a b c

c

d

a b

4

shape is cut in a nonround root.9 Inaddition, very few roots are actuallyround in cross section. The potentialof an endodontically-treated tooth tofracture increases proportionally tothe amount of dentin removed.1,2

This risk is even higher in ovoid roots(Figure 10).

Can We, Should We, Machine Onlythe Apical 2 mm of the Root?

Interestingly, the cross sections in theapical 3 mm of most roots becomeround and without flutings; regard-less of the ovoid shape and flutingsthat are present in the remainder ofthe root. Most clinicians and re -searchers will agree that some apicalshaping and taper is of benefit fromboth a disinfection and obturationstandpoint. From a strength and frac-ture resistance perspective, this is oneplace, perhaps the only place, wherethe root can be milled without deleteri-ous long-term affects.

What is the Ideal EndodonticShape and Technique?

In a unique and novel approach, Dr.Fred Barnett guest authored anendodontic edition of Dental Clinics ofNorth America. He requested that Dr.John Khademi (a restoratively-awareendodontist) and I (a general dentist)co-author chapters on modern accessand shaping. The 2 chapters we wrotefor the textbook are now availablefrom Elsevier publishing. The follow-ing are some highlights of thetext:10,11

• Visual endodontics (using amicroscope and modern instrumentsto find all of the major canal systemswithout mutilating the tooth).

• Biomimetic and minimally inva-

sive shapes (shaping of the canals withconstant microscopic visualization tomatch the root form, not milling arbi-trary big round tapering shapes).

• Vital cases and lesion cases arealmost unrelated.

• For lesion cases, we can expect a3 times higher failure rate, and thosecases should be treated in a specialmanor. Follow articles are planned.

• Vital cases (no lesion) should bekept as small as possible.

• A generous 45° cavosurface cutthrough etchable substrates (enameland some porcelains) allows a betterrestorative seal and aids in preserva-tion of PCD.

• For nonlesion cases, continuoustaper in small delicate roots and activeirrigation in any canal shape in thehope to clean and obturate lateralcanals is not warranted.

I Just Had My No. 19Extracted...and I’m Not Happy

Yes, I feel like an old man. Seven yearsago the pulp died in tooth No. 19 anda committed endodontist did a beauti-ful Resilon endo (Figure 11). It neverfelt quite right and recently developeda stoma on the facial. The endodontistand I faced the agonizing decision of

retreatment or extraction. (David: Isthe previous highlighted section cor-rect, as edited? DCA) One of the tip-ping points for extraction for me wasthe weakened coronal half of thesedelicate roots. Sure, we could try a re-treatment, but would the tooth last alifetime even if we deflated the cystson the mesial root? Photographs ofmy extracted tooth No. 19 and conebeam computed tomography (CBCT)will be featured in future articles.Suffice it to say that the mesial had avery large cyst attached.

The CBCT looked far worse thanthe periapical radiograph, so I opted forextraction. I now have a hole in mymandible where I used to have a beau-tiful molar. What are the morals of this

sad story? Resilon obturation, largetapering shapes, and a hermetic rootseal are not panaceas. Great endodon-tics fails, and it fails far more often thanit should. Let’s accept that some ofthese cases will never heal necroticcases with calculus on the root andextensive cysts. Some soul searchingmay be in order to decide which isworse: root fractures and prostheticfailures, or unfilled lateral canals? If atooth has a long parallel-sided delicatecanal system, do we return to the con-cept of an apical stop?

Reclaiming Endodontics Does Not Mean Stop Referring

to Endodontists!As an associate member of theAmerican Association of Endodontists(AAE), I am able to stay current on thesame activities and research that mem-ber endodontists receive. An interest-ing study done by the AAE showedthat people who have had a root canalby an endodontist are more satisfiedthan those who had the procedure

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John Khademi DDS, MS The treatment philosophies presented here are not an update of the traditional

endodontic technique. Dr. Clark and I believe that the traditional round-bur, tactile-

based approach to endodontic access is fundamentally flawed. We are proposing a

new approach of site-specific dentin conservation. Central to the philosophy is a titra-

tion of the treatment protocol to the given case from what we know about the histol-

ogy, the presenting pulpal and periradicular diagnosis, the endodontic-anatomic

issues and radicular-morphological form.

We know that we cannot completely debride the canal system. Decades of lit-

erature with multiple instrumentation techniques and the attendant shaping end-

points, varied irrigants and intracanal medicaments and consistently show this.

Consistent with this understanding of the real results of our woeful attempts at

debridement is the impartial evaluation of the truly long-term 20-plus-year-old

cases. As a group, these cases have obvious missed anatomy, are short, under-

shaped and poorly obturated by today’s standards.

Yet, looking past the endodontic shortcomings of these 20-plus-year-old

cases, one finds they invariably share this characteristic: adequate peri-cervical-

dentin (PCD) has been maintained. Violation typically occurs in 3 key areas: (1)

gouged access, (2) aggressive, obturation-driven shaping protocols, and (3)

deep axial reduction during crown preparation. Violation of the PCD in 3 or more

areas portends a drastically shortened lifespan for the tooth. This is evidenced

by the dearth of “good looking” 20-plus-year-old cases.

Balance needs to be restored to the treatment process that respects: (1)

The operator needs in accomplishing the treatment objectives appropriate given

what we know about the given case (above); (2) The tooth needs for long-term

retention; 3) The restoration needs from a fabrication and mechanical perspec-

tive.

Dr. Khademi is an endodontist and pioneer of Restoratively Driven Micro-Endodontics. He can

be reached at jakhademi@gmail.com.

Figure 9. Extracted immature maxillary molar

is sectioned and viewed from the apical.

Uniform wall thickness of root dentin is nearly

always present naturally in both young and old

teeth.

Figure 10. A relatively conservative arbitrary

round endodontic shape in an ovoid root com-

bined with inevitable noncentered enlargement

allows mesiodistal flexure and consequent buc-

colingual crack initiation.

Figure 11. Postoperative report from the endodontist (left 4 radiographs) shows a preoperative

view and 3 postoperative views of my tooth No. 19. It is a textbook Dr. Schilder shape. Note the

careful the shapes were and (David? DCA) that 4 canals were filled with matching puffs of sealer.

Seven years later (right single radiograph), there are significant lesions on the mesial root high-

lighted by the green arrows.

An Endodontist’s Perspective

5

done by a general dentist12 (only halfof patients who had a root canal bytheir general dentist would return tohim/her for the treatment!). My recom-mendations are: to first find an endo -dontist who uses a microscope forevery step of every case; and second,take him/her to lunch to discuss ourconcerns (as restorative dentists)regarding the long-term weakeningeffects of some current accepted phil -osophies of root canal access and shap-ing. (You might want to bring along acopy of this article.)

CLOSING COMMENTS Question yourself whenever you cuttooth structure. Very few of theendodontic techniques that we per-form have sufficient evidence to sup-port the dogmas that are the founda-tions of such techniques.�

References (not completed by dennis yet)1. Lirtchirakarn V. Patterns of vertical root frac-

tures: factors affecting stress distribution in theroot canal. J Endod 2003;29:523-8

2. Tamse A. An evaluation of endodontically treatedvertically fractured teeth. J Endod 1999;25:506-8

3. Biomimetic endodontics: the final evolution?Clark DJ. Dent Today. 2007 Jul;26(7):86-91.

4. Sathorn S. et al A comparison of the effects of 2canal preparations on root fracture susceptibilityand fracture pattern. J Endod 2005;31;4:283-7

5. Sedgley CM, Messer HH. Are endodonticallytreated teeth more brittle? J Endod 1992;18:332-5.

6. Huang TJ, Schilder H, Nathanson D. Effects ofmoisture content and endodontic treatment onsome mechanical properties of human dentin. J.Enod 1992;18:209-15

7. Fate of the tissue in lateral canals and apicalramifications in response to pathologic condi-tions and treatment procedures. Ricucci D,Siqueira JF Jr. J Endod. 2010 Jan;36(1):1-15.Review.

8. Treatment outcome in endodontics: the TorontoStudy. Phase 1: initial treatment. Friedman S,Abitbol S, Lawrence HP. J Endod. 2003Dec;29(12):787-93

9. Finite element analysis and strain-gauge studiesof vertical root fracture. Lertchirakarn V,Palamara JE, Messer HH. J Endod. 2003Aug;29(8):529-34.

10. Case studies in modern molar endodonticaccess and directed dentin conservation. ClarkD, Khademi JA. Dent Clin North Am. 2010Apr;54(2):275-89.

11. Modern molar endodontic access and directeddentin conservation. Clark D, Khademi J. DentClin North Am. 2010 Apr;54(2):249-73.

12. American Association of Endodontists NationalConsumer Awareness Survey, L.C. Williams &Associates Research Group, January 2009.

Dr. Clark is a general dentist and pioneer inbiomimetic microendodontics and minimallytraumatic restorative microdentistry. He canbe reached at he can be reached via e-mail atdrclark@microscopedentistry.com or visit theWeb site lifetimedentistry.net.

Disclosure: Drs. Clark and Khademi receive aroyalty from the sales CK Endodontic Accessburs and CK Endo-Exploration burs. For fur-ther information regarding these burs, contactSS White Burs at sswhiteburs.com.

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