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CENTRIC RELATION IS OBSOLETKALBERT I;. KADER, D.D.S.

Vancouver, British Colzcnzbia

A DVANCED STUDENTS in dentistry have been attempting by variousmeans to overcome the deficiencies of centric relation. None of these es-pedients are successful because centric relation, itself, is unsound in principle, butthey do have an encouraging portent ; they indicate that dentistry is finally realizingthe dangers of the centric relation concepts. More and more, those who arerestive under the failures of prevailing techniques are realizing that centric relationis merely a static position of the jaw that is useless in functional occlusion. Ilihatis far more important, they are also becoming aware that all efforts to maintaincentric relation and, at the same time, to have teeth in occlusion are impossible.

Let us suppose a patient to be edentulous. By using any of the conventionalmethods (including single or multiple intraoral or extraoral Gothic arch tracingsor any combination), the dentist has located centric relation to his entire satis-faction. Whether his methods involve so-called strained or unstrainedrelationships is of no importance here. To obviate argument, let it be concededthat the dentist has met every requirement of conventional teaching ; he has locatedcentric relation to perfection.

Ijow, the first insurmountable obstacle presents itself; namely, just how isthis centric relation to be transferred to the articulator wherein all restorationsconcerned with occlusion for the mouth must be made?

DIFFICULTY OF TRANSFERT\o part of this relationship can be transferred to an articulator, except thehorizontal relation of the alveolar ridges. Meanwhile, some definitions of centric

relation require that the condyles be in their most retruded positions in their fossae.This is a concept that is far removed from mere relationship of the alveolar ridgesin space. The distance from the rotational centers of the condyles, the naturalsymmetries and/or asymmetries existing between the two condyles, between thecondyles and the occlusal plane both laterally and anteroposteriorlp, and the abso-lutely necessary orientation of all these to some cranial reference plane have beentossed aside the instant the mounting in the articulator is attempted. To repeatand to emphasize, nothing but the horizontal relation remains, and that, too, willbe lost the instant the technician opens the articulator to set up the first tooth.

Received for publication Nov. 27, 1954.333

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334CUSPAL INTERFERENCR

There will be an objection at this point from some defender of centric relationHe will insist that the technician has taken precautions to see that the vcrticaidimension does not change while the teeth are being substituted for the occlusionrims. Let this be granted ; let vertical dimension be unchanged in the slightratdegree. But what is to be done about the cusps required on the teeth? QLI~Wclearly, these will intrude upon and adversely affect the all-important verticaldimension. Vertical dimension demands that these cusp tips bottom in thrfropposing fossae. The technician has set up the teeth, then, with tips of the cuspsin their opposing fossae and with vertical ditnension exactly as established 1)) theocclusion rims. To do this, the teeth have been arranged so that the cusps pas:each other and their opposing cuspal inclines on the way to the vertical dimensionof occlusion. Since the articulator in this case will open and close on an arc !111iteunlike the opening and closing arc in the hcatl, the cusps cannot fail to interfere.The truth of this is attested by the universal grief over cuspal interference :IIH~the widespread advocacy of some form of flat tooth in an egort to dodge it.

VARYING RADIIXow let it be assumed that an attempt has been made to meet the above

trouble by using such cusp perversions that the simple surfaced occlusion rinlsare practically duplicated by flat teeth. This is far from Ijeing a satisfactory answermechanically, not to mention the necrobiosis that will be forced by blunt teeth.Thus, a further error has been added to alibi for the primary error. The impossi-bility of compensating for the disparity of radii between the articulator hinge axesthat dictate how the teeth shall be set up in the instrument and the condylar hingeaxes that control these same teeth meeting in the head hecotnes apparent. Theradii will, most certainly, be unequal. Ti the articulator radius is shorter thazlthe head radius, the anterior teeth will strike too soon in function. If the artictr-later radius is longer than the head radius, the posterior teeth will strike too wwin function. These discrepancies are forecast by ordinary mathematics and cm-firmed by everyday results.

PROBLEMS IX FULL MOUTII RECONSTR1:CTIOXThe result just described will be worse than duplicated in a full mouth re-

construction of natural teeth wherein the operator attempts to circumvent thedefects of centric relation by working from a fixed crown position. In the firstplace, the occlusion of the preliminary crowns that decide the fixed position isfraught with inaccuracies, for the crowns must be constructed to a vertical dimen-sion that cannot help but be opened or closed from the original centric relationmounting. Second, there is no way to prove the accuracy of the jaw relationshipthat is to be used in forming the final crowns, for, with the preliminary crownocclusal surfaces held in static relationship by the jaws and locked for mountingwith plaster, there is no possible way of checking the jaw relationships. Addthe inevitable results of these error breeders to those already credited to the

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Volutne 5Yulllll~~~ 3 CEXTRIC RELATIONS IS OBSOLETE 335prosthodontist who works with centric relation, and the final mouth reconstructionstands little chance of being a success except in some chauvinistic operators mind.

Kow, to consider the conventional mounting for a full mouth reconstruc-tion. Let us suppose that the case under consideration is a natural mouthreconstruction where all working teeth are to be prepared and covered with fullcrowns. Before these crowns can be built, the teeth must be prepared, and im-pressions of the preparations and articulator mountings must be made. It willbe from these articulator mountings that wax crowns will be carved and occludedbefore casting and upon which the cast crowns will then be adjusted for occlusionin the mouth. In short, all of the detailed work must be done on some articulator.

ERRORS PRODUCED BY INTEROCCLUSAL RECORDSThe usual preliminary step is a centric relation record followed by the mount-

ing of casts in an articulator for the purpose of diagnosis and treatment planning.This centric relation record must be made with the teeth separated sufficientlyto prevent cuspal contact. Otherwise, the accuracy of the record will be ruinedby cuspal guidance. Rarely is the occlusal separation less than 2 mm., and inmany cases the separation will be 3 mm. or more, due to gross prematurities.

With this occlusal separation parting the upper and lower teeth, the centricrelation mounting has been made in the articulator. When the wax has beenremoved and the teeth have been permitted to occlude, the first gross error hasbeen introduced. As the centric relation record was transferred to the articulator,everything but the horizontal relation was lost, and now that vertical dimensionhas been changed, even the horizontal relation has been discarded. The result ismerely a crude approximation of the patients jaw relationships. How can a realstudy be made under such handicaps ? How can a really logical and safe diagnosisbe offered the patient?

Despite the dubiety of procedures so far, let us assume that both patient anddentists are agreed, and the restorations are scheduled for completion. The teethhave been prepared, and mounting casts have been made ready. Dies, copings, andtransfers, if used, are ready and assembled. Let there be no diversionary argu-ment on the quality of the necessary work up to this point; let all be presumedto be perfect. It now becomes necessary to make a secondary centric relationrecord, upon which the success of the whole restoration depends. The questionarises as to the choice of vertical dimension. This must be registered in themouth for transfer to the articulator.

Again, let there be no quibbling over the accuracy of the centric relationrecord so secured; let us accord it perfection. The only exception to this accordwill be a centric relation resulting from a physiologic rest position mounting.Since no part of centric relation except the horizontal relation can be transferredto an articulator, and since the articulator must be closed from 2 to 4 mm. fromphysiologic rest position to attain centric occlusion, then the changed verticaldimension will upset the horizontal relation, leaving nothing in its place. Butoverlooking the physiologic rest position diversion, let us return to the conventionalsituation and the assumed perfect centric relation mounting.

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The cycle is now complete. Once more, the questions arise ; what IIJ itsabout divergent radii, how to correct ior discrepancies in mounting th

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lolume 5Tumhcr 3 CEKTRIC RELATIOlrjS IS OBSOLETE 337which consists of a combined medial, vertical, and protrusive arc that incorporatesthe Bennett movements.

That Transographics is successful is evidenced by the almost universal cn-thusiastic reports from its users. Anyone who cannot succeed with Transo-graphics lacks either background or ability. The author was the first dentist,excepting only the co-inventor of the Transograph, to learn Transographics andthe operation of the Transograph. So far as he is concerned, centric relation,lateral motions, condyle paths, balance, and kindred precepts are wholly obsolete.The new concept of natural jaw function and an articulator capable of duplicatingthis function offers dentistry something that, for the first time, makes sense-and works.

These conclusions were arrived at after many years of attempting to workwith conventional precepts in dentistry; years of changing from one techniqueto another, trying to utilize the established methods and attempting to under-stand and rationalize why one restoration worked and the next did not.1666 WEST BROADWAYVANCOUVER 9, BRITISH COLUMBIA