612 THE JOURNAL OF PROSTHETIC DENTISTRY VOLUME 84 NUMBER 6

There has been debate in the literature about whichanteroposterior maxillomandibular relationship shouldbe used in fixed and removable prosthodontics.1 Manyprosthodontists have argued that complete denturesshould be fabricated with the mandible in the mostretruded position and that the teeth should be set upin maximal intercuspal position to coincide with thatposition.2-4 However, this view has been challengedon the basis that the position of maximal intercuspa-tion of the natural teeth occurs with the mandiblesignificantly anterior to the most retruded position5-8

and that forcible retrusion of the mandible puts theteeth in a more posterior occlusion. Several studiessupport the latter view,9,10 but they used dentate sub-

jects and located the retruded mandible at a retrudedcontact position (RCP) with the vertical dimensionincreased.

One previous study11 measured the retrusion at theocclusal surfaces of the teeth with the mandibleretruded but with the subject’s original vertical dimen-sion of occlusion (VDO) restored by occlusaladjustment. In 15 subjects, the range of retrusion wasfound to be between 0 and 0.4 mm (mean 0.2 mm).These results did not support the contention of a sub-stantial posterior shift of the mandible from maximalintercuspal position to the most retruded position.There was some shift, but only a very small amount.

Even these results do not provide any direct indica-tion of displacement of the mandibular condyles. Theycan be assumed to apply only to condylar displace-ment. The acquisition of a SAM2 Articulator andCondylar Position Indicator (SAM Prazisionstechnik,

Condylar repositioning in mandibular retrusion

Jeffrey Wilson, BDS, MSc, DDPH,a and Robert Ian Nairn, BDS, MScb

College of Medicine, University of Wales, Cardiff, Wales, and King’s College, London, England.

Statement of problem. There has been debate about which anteroposterior maxillomandibular rela-tionship should be used in fixed and removable prosthodontics for patients without a definite maximalintercuspation. The choice has important implications for complete denture fabrication in which anyguidance to the previous dentulous maximal intercuspal position is missing.Purpose. This study was designed to estimate the posterior displacement that takes place at themandibular condyles and occlusal surfaces when the mandible is moved from maximal intercuspal positionto the most retruded mandibular position.Material and methods. Articulated occlusal models of 18 subjects with a natural dentition and well-defined maximal intercuspation were studied. Models were rearticulated in retruded contact position, andthe original vertical dimension of occlusion was restored by eliminating all interfering occlusal contacts onthe retruded path of closure. Measurement of change in condylar position was estimated using a SAM2articulator with condylar position indicator. Posterior displacement at the occlusal surfaces was measuredwith a traveling microscope.Results. Condylar analog retrusion in the horizontal plane at the initial retruded contact position variedfrom 0.6 to 2.4 mm (mean 1.0 ± 0.4 mm); however, after occlusal adjustment to restore the original ver-tical dimension of occlusion, retrusion was reduced to a range of 0 to 0.4 mm (mean 0.2 ± 0.1 mm).Retrusion at the occlusal surfaces was found to vary from 0.4 to 1.5 mm (mean 0.7 ± 0.3 mm) at retrud-ed contact position; however, after occlusal adjustment, retrusion was reduced to a range of 0 to 0.5 mm(mean 0.2 ± 0.1 mm).Conclusion. Posterior displacement at both the occlusal surfaces and the condyles was small when inter-fering occlusal contacts on the retruded path of closure were removed. (J Prosthet Dent 2000;84:612-6.)

aLecturer in Restorative Dentistry, Department of Adult DentalHealth, College of Medicine, University of Wales.

bConsultant Emeritus in Prosthetic Dentistry, King’s College.

CLINICAL IMPLICATIONS

In major restorative procedures for which there is no existing definitive, functionalmaximal intercuspal position, the clinician should use the most retruded mandibularposition. Complete dentures should be fabricated with maximal intercuspal positioncoincident with the most retruded mandibular position.

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DECEMBER 2000 613

Munich, Germany), which allows measurement ofpositional change at condylar analogs, facilitated thetesting of this assumption.

MATERIAL AND METHODS

The SAM2 articulator (Fig. 1), a conventionalarcon pattern articulator, was used for cast mounting.The upper arm of the articulator was modified toaccommodate the use of a Dentatus face-bow withorbital pointer (AB Dentatus, Stockholm, Sweden).This modification allowed the maxillary casts to bepositioned in the articulator in the same relationship tothe arbitrary hinge axis that was established in a previ-ous study.11 The mounted casts at each stage of theinvestigation were transferred to the condylar positionindicator (Fig. 2). This instrument has 6 sensitive dialgauges (360-degree rotation = 1 mm linear displace-ment) that indicate movement of each condylar analogin 3 planes. The movements measured were thosebetween successive cast mountings.

Two studies were undertaken. The first, principalstudy used the SAM instruments to measure condylarshift. The second study, which used the same casts andrecords, measured shifts at the occlusal surfaces with atraveling microscope. In principle, these studiesrepeated the previously reported study11 using analternate method.

Measurement of condylar shift

Stone casts (Kaffir D Dental Stone, South WesternIndustrial Plasters, Bromham, England) were pro-duced from irreversible hydrocolloid (Caulk Seltrate,Dentsply International Inc, Milford, Del.) impressionsof 18 volunteers (undergraduate dental students anddental nurses ranging in age from 21 to 24 years) whohad reasonably intact and well-cared-for dentitionswith a clearly defined maximal intercuspal position. ADentatus face-bow record was made using the averagehinge axis position, as described by Beyron,12 andthe same reference points used in the previous study11

(13 mm from the most posterior border of the tragus ofthe ear on a line to the outer canthus of the eye).

The upper cast was mounted in the SAM articulatorusing the face-bow record; the lower cast then wasmounted with the teeth in maximal intercuspal posi-tion. Care was taken to ensure that the incisal pin ofthe articulator contacted the incisal table, thus estab-lishing a reference point for the VDO. The mountedcasts were removed from the articulator and attachedto the arms of the condylar-positioning instrument.They again were related in maximal intercuspal posi-tion, and the condylar dial gauge readings wererecorded.

A bite registration tray (Coe Laboratories Inc,Chicago, Ill.) was loaded on both sides with a metaloxide/eugenol paste (Kerr’s Bite Registration Paste,

Kerr Manufacturing Co, Romulus, Mich.) and placedover the occlusal surfaces of the mandibular teeth.Bilateral manipulation has been shown to be the mostconsistent method for achieving the most retrudedmandibular position.13 This method therefore wasused to manipulate each subject’s mandible into themost retruded mandibular position. A record wasmade at the point of initial occlusal contact, which iscommonly called the RCP. Care was taken to ensurethat the mandible was in its most retruded position(the operator-induced closing movement with the sub-ject relaxed).

The mandibular cast was remounted in the articu-lator with the casts seated in the retruded record(Fig. 3). The remounted casts then were transferredto the condylar position indicator. The new dial read-ings, indicating changes in condylar position, were

Fig. 1. SAM2 articulator.

Fig. 2. Condylar position indicator.

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614 VOLUME 84 NUMBER 6

recorded. The casts were replaced on the articulator,and the original VDO was reestablished by modify-ing the occlusal surfaces of the teeth until allinterfering contacts on the retruded path of closure(terminal hinge axis movement) were eliminated.This was achieved by ensuring that the incisal pinreestablished contact with the incisal table. Theadjusted casts again were transferred to the condylarposition indicator, and the dial readings once morewere recorded.

Measurement of shift at occlusal surfaces

At each stage previously outlined (namely, maximalintercuspal position, RCP, and restored VDO), theSAM articulator was placed on a platform in a fixedrelationship to the eyepiece of a traveling microscope(Fig. 4). Small crosses marked on the buccal surfacesof all first premolars were located in the eyepiece cross

hairs, and their successive shifts were recorded. Eachmeasurement was repeated an additional 2 times, andthe mean value of the shifts was calculated.

RESULTS

The findings showed changes in position at thecondylar analogs and at the occlusal surfaces betweenmaximal intercuspal position and RCP and betweenmaximal intercuspal position and the most retrudedmandibular position after the original VDO wasrestored. Results are summarized in Tables I through III.

Condylar analog retrusion in the horizontal planeat RCP was found to have a range of 0.6 to 2.4 mmwith a mean of 1.0 ± 0.4 mm. After occlusal adjust-ment to restore the VDO, the range was reduced to0 to 0.4 mm with a mean of 0.2 ± 0.1 mm.

Retrusion at the occlusal surfaces was found to havea range of 0.4 to 1.5 mm with a mean of 0.7 ± 0.3 mmat RCP. After occlusal adjustment to restore the VDO,the range was reduced to 0 to 0.5 mm with a mean of0.2 ± 0.1 mm.

LIMITATIONS OF THIS STUDY

This study used stone occlusal models of youngdentate subjects with reasonably intact dentitions andgood maximal intercuspation. The SAM2 articulatorwith condylar position indicator that used condylaranalogs was used to estimate condylar shift. This studycould not be carried out in vivo; thus it was not possi-ble to directly measure condylar shift. It would beunethical and unnecessarily destructive to alter theocclusion of individuals who do not have pathologicocclusal disturbances.

DISCUSSION

The use of an arbitrary face-bow was deliberatebecause the authors wished to copy as closely as possi-ble the method of the previous study11 and becausethe use of the kinematic face-bow in determining thetrue hinge axis location is a notoriously error-proneprocedure.14 The average hinge axis position is said topass through the condyles. If the average axis is with-in 5 mm of the true axis, the maximum error at theocclusal surfaces would be of the order of 0.05 mm,15

a negligible amount.For the purposes of this study, the mandible was

regarded as a rigid structure. The face-bow recordusing the average hinge axis gave a 3-dimensional sta-tic model, which allowed the assumption that thecondylar analog shifts accurately reflected any truecondylar shifts.

The criticism that older patients with partially den-tate mouths may have a larger horizontal shift betweenmaximal intercuspal position and centric relation is notrelevant to this study. The aim of the study was todemonstrate that, in subjects with reasonably intact

Fig. 3. Remounted casts in retruded contact position.

Fig. 4. Traveling microscope measuring occlusal shift atRCP.

WILSON AND NAIRN THE JOURNAL OF PROSTHETIC DENTISTRY

DECEMBER 2000 615

dentitions, any difference is very small. Should they sub-sequently lose most or even all of their natural toothcontacts, such subjects should be able to adapt com-fortably to restorations with maximum intercuspationcoincident with the most retruded mandibular position.

Condylar analog shift

The most important feature of these results is theclear demonstration that any shift is very small. Thecondylar horizontal shift compares closely to occlusalretrusion after occlusal adjustment. The range ofretrusions at RCP was much larger than the range afterocclusal adjustment. As there was an opening compo-nent and a retrusive component at RCP, this couldhave involved some translation of the condyles as wellas a hinge rotation. After occlusal adjustment torestore the VDO, the condylar displacements becamesmall in all measured dimensions.

Occlusal shift

The horizontal occlusal shift at RCP was much larg-er than that after restoration of the VDO. After occlusaladjustment, the range became very small. For themajority of subjects, the amount of occlusal adjustmentrequired to restore the original VDO was minimal; itconsisted mainly of the removal of premature interfer-ing contacts on the retruded path of closure.

The much larger shifts obtained at RCP explain thecommonly held but mistaken opinion that maximal

intercuspal position is significantly forward from themost retruded mandibular position.

The results obtained in this study are strikinglysimilar to those reported in the previous study11 andthus reinforce the previously reported results andconclusions.

CONCLUSIONS

This study and its previously reported countepart11

confirm that, when the mandible is moved from max-imal intercuspal position to retruded contact position,any shift at the occlusal surfaces or the condyles is verysmall if interfering contacts on the retruded path ofclosure have been eliminated.

These results strongly support the argument for mak-ing maximal intercuspal position coincident with themost retruded mandibular position when undertakingmajor restorative procedures (namely, full-mouth reha-bilitation) in which there is no existing definitive,functional maximal intercuspal position. The findingsare especially relevant to the fabrication of completedentures where any guidance to the previous dentulousmaximal intercuspal position is missing.

We thank Dr Julian Woelful of Columbus, Ohio, for his gener-ous gift of the SAM instruments.

REFERENCES

1. Kydd WL, Sander A. A study of posterior mandibular movement fromintercuspal occlusal position. J Dent Res 1961;40:419-25.

Table I. Condylar analog repositioning (mm) (n = 18)

Retruded contact position After occlusal adjustment

Minm Maxm Mean SD Minm Maxm Mean SD

Vertical 0.8 2.2 1.1 0.4 0 0.5 0.2 0.1Lateral 0 0.7 0.3 0.2 0 0.4 0.2 0.1Horizontal 0.6 2.4 1.0 0.4 0 0.4 0.2 0.1

Condymeter method.

Table II. Occlusal retrusion (mm) (n = 18)

Retruded contact position After occlusal adjustment

Minm Maxm Mean SD Minm Maxm Mean SD

0.4 1.5 0.7 0.3 0 0.5 0.2 0.1

Microscope method.

Table III. Comparison of data for horizontal retrusion (mm) (n = 18)

Condylar analog retrusion Occlusal retrusion

Mean Range Mean Range

RCP 1.0 (± 0.4) 0.6-2.4 0.7 (± 0.3) 0.4-1.5VDO restored 0.2 (± 0.1) 0-0.4 0.2 (± 0.1) 0-0.5

RCP = Retruded contact position; VDO = vertical dimension of occlusion.

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616 VOLUME 84 NUMBER 6

2. Helkimo M, Ingervall B, Carlsson GE. Variation of retruded and muscu-lar position of mandible under different recording positions. ActaOdontol Scand 1971;29:423-37.

3. Lucia VO. Gnathological concepts of articulation. Dent Clin North Am1962;6:183-97.

4. Boos RH. Centric relation and functional areas. J Prosthet Dent1959;9:191-6.

5. Mack PJ. A discussion of some factors of relevance to the occlusion ofcomplete dentures. Aust Dent J 1989;34:122-9.

6. Noble WH. Anteroposterior position of “Myo-Monitor centric.” J ProsthetDent 1975;33:398-402.

7. Parker ML, Hemphill CD, Regli CP. Anteroposterior position of themandible as related to centric relation registrations. J Prosthet Dent1974;31:262-5.

8. Dykins WR. A consideration of centric relation. J Prosthet Dent1968;20:494-7.

9. Hoffman PJ, Silverman SI, Garfinkel L. Comparison of condylar positionin centric relation and centric occlusion in dentulous subjects. J ProsthetDent 1973;30:582-8.

10. Hodge LC Jr, Mahan PE. A study of mandibular movement from centricocclusion to maximum intercuspation. J Prosthet Dent 1967;18:19-30.

11. Wilson J, Nairn RI. Occlusal contacts in mandibular retrusion. Int JProsthodont 1989;2:143-7.

12. Beyron H. Orientational problems with prosthodontic reconstructionand occlusal analysis. [from Swedish] Swed Dent J 1942;35:1-55.

13. Kantor ME, Silverman SI, Garfinkel L. Centric relation recording tech-niques: a comparative investigation. J Prosthet Dent 1973;30:604-6.

14. Preston JD. A reassessment of the mandibular transverse horizontal axistheory. J Prosthet Dent 1979;41:605-13.

15. Brotman DN. Hinge axes. Part II: geometric significance of the transverseaxis. J Prosthet Dent 1960;10:631-6.

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THE DENTAL SCHOOL, UNIVERSITY OF WALES

COLLEGE OF MEDICINE, HEATH PARK

CARDIFF CF 4 4XY WALES, UNITED KINGDOMFAX: (12)2-274-3120 E-MAIL: wilsonj@cardiff.ac.uk

Copyright © 2000 by The Editorial Council of The Journal of ProstheticDentistry.

0022-3913/2000/$12.00 + 0. 10/1/111501

doi:10.1067/mpr.2000.111501

Complete dentures: Pre-definitive treatment—rehabilitationprosthesis (part 3)McCord JF, Grant AA. Br Dent J 2000;188:419-24.

Purpose. The authors describe the decision-making process before formulating a treatment planfor an edentulous patient. The plan includes oral tissue rehabilitation (for both soft and hard tis-sues) and other preprosthetic measures sometimes termed “rehabilitation devices.”Discussion. The authors describe common soft and hard tissue conditions that may need to becorrected before new complete dentures can be fabricated. The soft tissue conditions include tis-sue distortion, denture-related stomatitis, angular chelitis, fibrous degeneration of the residualridges, border defects, and hyperplasia of the border tissues. Hard tissue conditions includeunerupted teeth and retained roots, sharp alveolar ridges, enlarged tuberosities, tori and otherbony prominences, and sharp mylohyoid ridges. The authors describe the use of rehabilitationdevices (transitional dentures) such as conditioning dentures, occlusal pivot dentures, and stentsto help correct/control hard or soft tissue conditions. The authors also offer these helpful sug-gestions: (1) Attempt to restore soft tissue to appropriate levels of oral health before makingdentures. (2) If hard tissue enlargements are such that interarch space will not permit minimaldenture bases, or if the tongue space is constrained, then preprosthetic surgery may be necessary.(3) Occlusal pivot appliance therapy may be useful when the patient has worn dentures for a longtime and there is good justification, from a medicolegal standpoint, for copying the existing den-tures and modifying the copy. The patient’s original denture remains unaltered in the event thatthere is an unsuccessful outcome. 2 References. —RP Renner

Noteworthy Abstractsof theCurrent Literature