Maxillomandibular relationship philosophies for prosthodontictreatment: A survey of dental educators

Philip S. Baker, DDS,a M. Harry Parker, DDS, MS,b John R. Ivanhoe, DDS,c andF. Michael Gardner, DDS, MAd

Medical College of Georgia, Augusta, Ga; Department of Veterans Affairs Medical Center,Augusta, Ga

Statement of problem. A variety of treatment philosophies persist concerning the need for coincidence ofcentric occlusion (CO) and maximum intercuspation (MI) in prosthodontic restoration; however, no consensusexists.

Purpose. The purpose of this study was to determine the philosophies of dental educators throughout theUnited States at both the predoctoral and postdoctoral levels and to compare their attitudes toward desirablemaxillomandibular relationships in defined clinical situations.

Material and methods. A survey was constructed with 5 clinical scenarios presented describing patients witha difference between maximum intercuspation and centric occlusion. The survey was mailed to 171 dentistsinvolved in either predoctoral or postdoctoral dental programs in the United States; including 56 dental schools;the Army, Navy, and Air Force postdoctoral programs; 8 Department of Veterans Affairs postdoctoral programs;and 7 hospital-based programs. Descriptive statistics of the responses were provided. Chi-squared (a=.05) andFisher’s exact test analyses (a=.05) comparing predoctoral and postdoctoral program responses for eachquestion were performed.

Results. Forty-three predoctoral dental school program responses were received. Forty-one postdoctoralprogram directors, including the dental school–based programs, 3 armed service branches, 2 VeteransAdministration programs, and 1 hospital-based program responded to the survey. Fifteen respondents indicatedthat they represented both predoctoral and postdoctoral programs, and these data were deleted from thesample. Summarized results for each question reflect on whether the clinicians philosophically believed patientswere better off with the elimination of an existing occlusal interference between MI and CO or not. There wasno statistically significant difference seen between the predoctoral and postdoctoral responses.

Conclusion. The controversy regarding the preferred mandibular position for treatment of dentulous andpartially edentulous patients continues among dental educators at both the predoctoral and postdoctoral levelsin the United States. (J Prosthet Dent 2005;93:86-90.)

CLINICAL IMPLICATIONS

Based on this study, there is a continuing lack of concensus among dental educators as to whetherCO and MI should be coincident at the definitive treatment position.

Advances in prosthodontics cannot solely be viewedas a simple refinement of materials and techniques. Anintegral part of such progress is the development of ter-minology and treatment philosophies that accuratelydepict current understanding. Occlusion is one of the

aAssociate Professor, Department of Oral Rehabilitation, School ofDentistry, Medical College of Georgia.

bClinical Associate Professor, Department of Oral Rehabilitation,School of Dentistry, Medical College of Georgia; Staff Prostho-dontist, Department of Veterans Affairs Medical Center, UptownDivision.

cProfessor, Department of Oral Rehabilitation, School of Dentistry,Medical College of Georgia.

dAssociate Professor, Department of Oral Rehabilitation, School ofDentistry, Medical College of Georgia.

86 THE JOURNAL OF PROSTHETIC DENTISTRY

most controversial and continuously evolving areas ofprosthodontics. As knowledge of this subject increases,terminology and treatment philosophies have requiredconstant revision to accommodate this new understand-ing. Although a relative uniformity of occlusal terminol-ogy has been established, treatment philosophies differgreatly. The variety of philosophies is likely a conse-quence of the limited evidence-based research and thelarge volume of anecdotal information available.

A basic tenet of occlusal philosophies is the concept ofa maxillomandibular treatment position.1 Even beforethe invention of the dental articulator in the early1800s, dentists attempted to make intraoral maxillo-mandibular records.2,3 These attempts and later refine-ments were driven by the observation that edentulouspatients had a difficult time repeating a closure position,

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but that a repeatable closure position was highly desir-able for stability of the denture bases.4 This repeatableposition became known as centric relation position.2

As dentists became more capable in the restoration ofnatural teeth, this concept was extended to dentate pa-tients. Centric relation is defined as ‘‘the maxilloman-dibular relationship in which the condyles articulatewith the thinnest avascular portion of their respectivediscs with the complex in the anterior-superior positionagainst the shapes of the articular eminences. This posi-tion is independent of tooth contact. This position isclinically discernible when the mandible is directed su-perior and anteriorly. It is restricted to a purely rotarymovement about the transverse horizontal axis.’’5

However, the use of centric relation as the accepted po-sition for prosthodontic treatment of dentate patients isnot as universally accepted as it has been for edentulouspatients.6 One philosophy suggests that all patientsshould be equilibrated or restored so that centric occlu-sion (CO) and maximum intercuspation (MI) are coin-cident.7 Another concept makes these positionscoincident only with a diagnosis of occlusal abnormalityorwhen restoringmultiple posterior teeth,8 and a similarrationale holds that patients should be restored at theposition of maximum intercuspation if a stable relation-ship exists.9 The treatment position for patient functionadvocated by Wood1 may or may not coincide with thepatient’s centric relation.

A recent extensive review of the literature by KeshvadandWinstanley10 provides several plausible explanationsfor the ongoing divergence of opinions. The authorsstate that present interpretations of mandibular treat-ment position are a reflection of the dental literature,in which some authors assert a CO-MI discrepancyshould be eliminated because this should be interpretedas a sign of occlusal disharmony.1,11-13 Other authorsview a discrepancy as a normal state resulting from a bal-ance of functional forces that should be maintained inthe absence of dysfunctional signs or symptoms.14-18

The purpose of this study was to determine the phi-losophies of dental educators throughout the UnitedStates at both predoctoral and postdoctoral levels, andto compare attitudes toward desirable maxillomandibu-lar relationships in defined clinical situations.

MATERIAL AND METHODS

A survey was designed with 5 clinical scenarios pre-sented describing patients with a discrepancy betweenmaximum intercuspation (MI) and centric occlusion(CO). A question was created for each of the 5 scenariosrequesting the preferred position, MI or CO, in whichto restore the patient, and multiple choices were pro-vided (Fig. 1). All questions except question 2 had an‘‘Other . Please explain’’ choice. Approval from the

JANUARY 2005

Medical College of Georgia’s Human AssuranceCommittee was obtained for this study.

The survey was mailed to 171 dentists, chairpersonsof departments involving occlusion or prosthodonticsin predoctoral dental programs, or directors of postdoc-toral dental programs in the United States. The direc-tory of the American Association of Dental Schoolswas used in part to help identify the schools and theheads of departments and programs. For postdoctoralprosthodontic programs, the directors surveyed in-cluded those from the Army, Air Force, and Navy pro-grams, 7 Department of Veterans Affairs programs, 7hospital-based programs, and 34 programs associatedwith dental schools.

Organization of predoctoral programs varied. Foreach school, questionnaires were mailed to all identifieddepartment chairs of occlusion, prosthodontics, restor-ative dentistry, or similarly titled sections involved inthe determination of occlusal philosophy used in thetreatment of prosthodontic patients. The introductoryletter requested that if there were individuals more fa-miliar with the predoctoral philosophy, the surveyshould be passed on to them. The data were analyzedwith chi-square and Fisher’s exact tests using statisticalsoftware (NCSS 2001; NCSS Statistical Software,Kaysville, Utah) with a significance level of a=.05.

RESULTS

Fifty-three total predoctoral responses were receivedfrom the 55 predoctoral programs surveyed. The re-sponses came from only 43 of the 55 predoctoral pro-grams. Fifty-seven responses from postdoctoralprograms were received from all 3 of the armed servicesprograms, 3Department of Veterans Affairs programs, 2hospital-based programs, and 33 postdoctoral programsassociated with dental schools. Fifteen responses indi-cated they represented both predoctoral and postdoc-toral programs, and they were deleted from the sample.

The responses for questions 1-5 are presented inTable I and summarized in Table II. The number of re-sponses for each choice is broken down for each of thecategories of faculty answering the question: postdoc-toral or predoctoral. Even though the letter explainingthe questionnaire stated that centric occlusion was de-fined as the first contact of the teeth with the mandiblein centric relation position, there were multiple com-ments indicating some confusion on the part of the re-sponders. For question 2, typical comments fromthose programs selecting answer B, ‘‘eliminate CO-MIslide,’’ or C, ‘‘do occlusion procedures other than[listed] above,’’ often included first evaluating and treat-ing the temporomandibular dysfunction.Occlusal splinttherapy was often recommended, followed by reevalua-tion of occlusion to determine the need for occlusalequilibration. Only 18 predoctoral educators answered

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QUESTIONNAIRE ON PHILOSOPHY OF USINGCO VERSUS MIP IN PROSTHODONTIC RESTORATIONS

IN THE FOLLOWING CLINICAL SITUATIONS, PLEASE SELECT THE MOSTAPPROPRIATE CHOICE OF HOW YOU OR YOUR SCHOOL CHOOSES AN OCCLUSALSCHEME FOR PROSTHODONTIC RESTORATIONS.

Unless otherwise stated, assume that these hypothetical patients show no evidence of excessive tooth wear, noTMD symptoms and no evidence of occlusal related tooth mobility.

1. You have a 55-year-old completely edentulous patient who has worn the same dentures for the past 15 years. Theteeth are worn, the VDO is decreased, and the posterior teeth interdigitate best at an MI position 1 mm anteriorto centric occlusion. You are going to fabricate newmucosal borne dentures with cusped teeth. Your maxillomandib-ular position of choice is:

a. MIP coincident with CO

b. MIP 1 mm anterior to CO

c. Other . Please explain

2. You have a 26-year-old patient who has 28 intact teeth with minimal conservative restorations. She has a Class I jawrelationship and a Class I tooth relationship. She has a .5 mm slide from CO toMIP, with a portion of the slide beinganterior and a portion being in a lateral direction. She has anterior disclusion in all excursive movements. She presentswith classic signs and symptoms of acute TMDof approximately 1month’s duration. In treating her TMDwould you:

a. Eliminate the CO-MIP slide

b. Leave her occlusion as is

c. Do occlusion procedures other than above

3. You have a 50-year-old patient with a full compliment of maxillary teeth in good alignment. He is missing all man-dibular molars and the right second premolar. He desires a removable partial denture replacing his mandibular pos-terior teeth. He has a .5 mm slide between CO and MIP. Would you:

a. Fabricate RPD to existing MIP occlusionb. Equilibrate to MIP = CO prior to making RPDc. Other . Please explain

4. You have a 38-year-old patient who ismissingmaxillary right and left thirdmolars andmandibular right and leftfirst and third molars. He desires to have mandibular right and left first molars replaced with tooth-borne fixedpartial dentures. He has a .5 mm slide from CO to MIP. How would you establish his occlusion in the FPD?a. Equilibrate the dentition prior to tooth preparation to make MIP = COb. Do the tooth preparation in both quadrants to eliminate all posterior interferences and make the

interocclusal record at CO and restore the occlusion at CO = MIPc. Do the FPDs one side at the time, retaining the patient’s existing MIPd. Other . Please explain

5. You have a 35-year-old patient who is missing her maxillary right central incisor and desires a tooth-borne FPD toreplace it. She has a .5 mm slide fromCO toMIP. InMIP her maxillary andmandibular anterior teeth contact, whichcreates anterior disclusion in all eccentricmovements. Throughmounted diagnostic casts, it has been determined thatby equilibrating the posterior teeth until CO = MIP at the existing VDO, the anterior teeth will no longer be in con-tact at MIP. How would you establish her occlusal relationship on the new maxillary anterior FPD?

a. Equilibrate the dentition so that CO = MIP and leave all anterior teeth out of MIP contact

b. Equilibrate the dentition so that CO = MIP and restore the lingual surfaces of maxillary right and left central andlateral incisors and canines, including the new FPD, to restore MIP contact

c. Equilibrate the dentition so the CO = MIP and restore MIP contacts on the new FPD, leaving the maxillaryright and left canines and left lateral incisor out of contact in MIP

d. Restore the patient in her existing MIP position

e. Other . Please explain

School: ____________________________________________________________________________________________

Position: ___________________________Postdoctoral _______________________Predoctoral

Position Title: _______________________________________________________________________________________

Fig. 1. Questionnaire on philosophy of using CO versus MIP in prosthodontic restorations.

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question 2. For question 3, 10 comments were received.A typical comment was to create a ‘‘long centric.’’ Forquestion 4, there were few comments and none of thesewas repeated. For question 5, several respondents com-mented that they selected answerD, ‘‘restore the patientin their existing MIP position,’’ assuming that the pa-tient was asymptomatic.

In Table II, the responses were categorized as CO orMI. For question 4, answers A andB indicatedCO as thepreferred treatment position, whereas C maintained thepatient’s existing MI position. Answers A, B, and C inquestion 5 designated CO, and answer D representeda choice of MI. All responses of ‘‘Other . Please ex-plain’’ (questions 1, 3, 4, and 5) and ‘‘Do occlusion pro-cedures other than above’’ (Question 2) were excludedfrom the statistical analyses. Chi-square and Fisher’s ex-act test statistical analyses showed no significant differ-ence in the answers of the predoctoral or postdoctoralfaculty groups.

DISCUSSION

Currently, searching for the truth relative to occlu-sion does not substitute for knowledge obtained from

Table I. Responses to questions

Responses to question 1

Level A B C Total

Predoctoral 36 2 0 38

Postdoctoral 37 1 4 42

Both 12 1 2 15

Total 85 4 6 95

Responses to question 2

Level A B C D Total

Predoctoral 5 13 19 0 37

Postdoctoral 6 22 14 0 42

Both 3 3 8 1 15

Total 14 38 41 1 94

Responses to question 3

Level A B C Total

Predoctoral 15 21 2 38

Postdoctoral 15 24 2 41

Both 9 5 0 14

Total 39 50 4 93

Responses to question 4

Level A B C D Total

Predoctoral 13 5 17 2 37

Postdoctoral 13 14 13 2 42

Both 6 2 6 1 15

Total 32 21 36 5 94

Responses to question 5

Level A B C D E Total

Predoctoral 3 0 2 33 0 38

Postdoctoral 2 5 0 33 2 42

Both 1 2 0 11 0 14

Total 6 7 2 77 2 94

JANUARY 2005

evidenced-based research, but agreement in a surveycan reflect the current understanding of treatment phi-losophy. There was a difference as to whether or notthe respondents believed patients were better off withthe elimination of an existing occlusal interference sothat centric occlusion and maximum intercuspationwould be coincident at the definitive treatment position.Assuming the respondents are competent clinicians, pa-tients similar to those types seen in the survey could besuccessfully treated by either philosophy, either restor-ing them at their existing MI position (retaining the oc-clusal interference from MI to CO) or equilibrating theteeth to make MI and CO coincident (eliminating theocclusal interference from MI to CO) prior to restora-tion. In the opinion of the authors, because both treat-ment modalities are feasible, it would seem prudent toavoid occlusal equilibration of natural teeth and to re-store patients at their existing MI positions when possi-ble.

Numerous investigators have reported that the ma-jority of dentate patients demonstrate a discrepancy be-tween CO and MI positions.8,13-17 The question iswhether this movement between CO and MI is poten-tially harmful to patients or perhaps physiologically ben-eficial. A possible hypothesis as to why it might bebeneficial is proposed by the authors. The condylemust slide slightly forward to accommodate the MI po-sition. As the elevator muscles exert force on the mandi-ble while the patient clenches in MI, the mandible flexesand elongates, and the condyles move posteriorly. Thesmall distance from MI to CO provides the space re-quired for the condyle to move.

There is no present evidence to confirm that MI-COocclusal interferences are either harmful or beneficial.Until research provides a definite diagnosis of some pa-thosis, it is the authors’ opinion not to equilibrate or pro-vide treatment to eliminate a condition found in mostindividuals that may be beneficial. There are some pa-tients that lack anMI position, and in restoring these pa-tients it is a prosthodontic necessity to use CO.However, for dentate patients with an existing MI

Table II. Summary of responses

Respondents

MI/CO

coincident

MI/CO not

coincident

Question 1 Predoctoral 38 36 2

Postdoctoral 38 37 1

Question 2 Predoctoral 18 5 13

Postdoctoral 28 6 22

Question 3 Predoctoral 36 15 21

Postdoctoral 39 15 24

Question 4 Predoctoral 35 18 17

Postdoctoral 40 27 13

Question 5 Predoctoral 38 5 33

Postdoctoral 40 7 33

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THE JOURNAL OF PROSTHETIC DENTISTRY BAKER ET AL

position, equilibration to remove a slide may not be in-dicated.

Differences between predoctoral and postdoctoralresponses might have been expected for several reasons.Patient screening for predoctoral programs tends toeliminate complex occlusal patient treatment. Becausethese patients are not encountered in the predoctoralclinics, no definitive philosophy for such treatmentwould be necessary at that level. Additionally, perhapsfewer predoctoral programs may have had access to a cli-nician skilled in treating temporomandibular disordersto complete the survey. Interestingly, a tendency ofboth predoctoral and postdoctoral educators surveyedto eliminate the discrepancy between CO and MI posi-tions appeared to decrease as the number of remainingnatural teeth increased.

The limitations of this study include the fact that par-ticipants may not have understood the questions.Confusion could have arisen owing to changing defini-tions of terms used such as CO, which previously wasused to indicate MI. In looking for differences betweenpredoctoral and postdoctoral programs, some individu-als responded as representing both programs. These re-sponses were excluded from the sample.

Because of the continuing lack of agreement amongeducators after several decades, the authors suggestthat future research should include more evidenced-based occlusion studies. An investigation into why thesediffering philosophies continue to exist would also be in-teresting.

CONCLUSIONS

Within the limitations of this study, the followingconclusions were drawn:

The controversy regarding the preferred mandibularposition for treatment of dentulous and partially dentu-lous patients continues among dental educators at boththe predoctoral and postdoctoral levels.

There was no significant difference between the pre-doctoral and postdoctoral responses for the clinical sit-uations presented in the survey.

90

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Reprint requests to:

DR PHILIP S. BAKER

MEDICAL COLLEGE OF GEORGIA

SCHOOL OF DENTISTRY

1120 15TH ST

AUGUSTA, GA 30912-1250

FAX: (706) 721-6276

E-MAIL: pbaker@mail.mcg.edu

0022-3913/$30.00

Copyright � 2005 by The Editorial Council of The Journal of Prosthetic

Dentistry.

doi:10.1016/j.prosdent.2004.11.002

VOLUME 93 NUMBER 1