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THE CUSPLESS CENTRALIZED OCCLUSAL PATTERNCHASTAIN G. PORTER, D.D.S.*

Uhwsity of Katasas City, School of Dedstry,Kansas City, MO.

PART ITHE PROCEDURET HE IMMEDIATE OBJECTIVE of an occlusion is the provision of aneffective chewing mechanism. The long-range objective, of even greater im-

portance, is the preservation of the residual structures in a state of optimumhealth. The cuspless centralized type of occlusion is a logical approach to attain-ment of both objectives.

VERTICAL JAW RELATIONIntraoral central bearing plates are attached to bases upon which anteriorwax rims have been built (Fig. 1). These are positioned to parallel the mean

foundation plane areas of both ridges.The vertical jaw relation is determined by a correlation of physiologic, esthetic,

mechanical, and phonetic factors.The rest position is first determined as accurately as possible by using

Pleasures* method of measuring from reference points on the nose and chin.This measurement is now decreased 3 or 4 mm. to determine the occlusalvertical position. The wax rims are inserted and trimmed for estheticlength and contour. Parallelism of the central bearing plates and of the under-lying ridges is hoped for at this time, The caliper is returned to the face, andall factors are carefully considered. Some revision of thinking may now be inorder. If compromise is necessary, it should usually favor the physiologic factors.Phonetic tests are deferred until the time of try-in. The central bearing stylusis now adjusted to maintain this vertical relation, after which a slight reductionin the height of the mandibular wax rim is made. Contact exists now only atthe central bearing point, and thus both bases are stabilized.

Read before the American Denture Society, Miami Beach, Fla., Nov. 6, 7954.Received for publication Aug. 23, 1954.*Clinical Professor of Dental Prosthesis.313

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A Gothic arch tracing is scribed by the stylus on the blackened central bcar-ing plate on the lower base. The bearing plate is then indented at the apt dthe tracing which is the centric point. N%h the patient exerting a light ci~siugpressure, and with the stylus in the indentation at the apex of the tracing, plasteris introduced between the bases with a syringe to record centric relation, andto attach the bases to each other in this position. No eccentric checkhitch ;trcmade, and a face-bow transfer is not used. Only the unstrained rctruded centricrelation of the jaws at the predetermined vertical level is desired. The asscn~hlage,including the casts, is positioned and mounted arbitrarily on an accurate articu-lator. The articulator is regarded as a maintainer of the static centric jalv TX:-lation, and not as a reproducer of functional jaw movements.

Fig. l.-The intraoral central bearing and tracing device attached to the basesprior to securing the jaw relation record.

Fig. Z.-The mandibular working occlusal surfaces are lingualThe buccal halves of the teeth are the suhocclusal surfaces. to the ridge fulcrum.

TOOTH ARRANGEMENT AND OCCLUSIONThe anterior teeth are positioned for best esthetics and facial support, but

without a vertical overlap. There should be no incisal contact in centric occlusion.Posterior teeth are used which possess the following specifications : ( 1) nocusp height ; (2) sharp cutting ridges ; (3) free sluiceways ; (4) working occlusal

areas constituted of the lingual halves of the lower teeth; (5) sub-occlusal areasconstituted of the buccal halves of the lower teeth ; and (6) balancing~elements tofunction only for balance in eccentric positions.

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CUSPLESS CENTRALIZED OCCLUSAL PATTERN 315These posterior teeth are aligned over the center of the mandibular ridges,

observing Sears basic principles. The mandibular working occlusal surfaces areplaced entirely to the lingual side of the ridge fulcrum without encroaching uponthe tongue (Fig. 2). The lower level of the subocclusal surfaces of the mandibu-lar teeth creates a reverse occlusal pitch not unlike the Pleasure or Boswell schemeof occlusion, which directs the occlusal forces downward and toward the lingual.

Fig. 3.

Fig. 4.Fig. 3.-The flat occlusal plane paralleling the ridges with the teeth in centric occlusion.

There is no contact of the second molars or of the anterior teeth.Fig. 4.-There is a firm contact of the balancing ramps in protrusive or lateral positions.There is a light contact on the anterior teeth in protrusion.

The occlusal pattern is oriented and limited to occupy only the horizontal foun-dation areas of the ridges. The bicuspids and first molars will usually fillthis .segment, but additions or omissions of teeth may be made. A flat occlusalplane, paralleling the mean foundation planes of both jaws, is developed on theentire working occlusal pattern. This complies with the principle of applyingforce at right angles to the support. Balancing elements or ramps are providedby inclining the occlusal surfaces of the lower second molars upward at about a30 degree angle, as advocated by Hardy. The upper second molars are set outof any possible occlusal contact and are frequently omitted. The occlusion isthus centralized from all aspects, antero-posteriorly and bucco-lingually (Fig. 3).At the time of the try-in, a careful check is made to assure a firm contact of the

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IAancing ramps in the various positional closures iPig. 4). lf necessary, alttr-ations are made to assure l~osterior halance with a light sitnultaneous ini isalcontact.

After the correction of any dimensional change incident to processing [hedentures, the occlusion is perfected at the chair (Fig. 5:). A central bearing point.device is attached to the dentures with modeling plastic. Starting with a slightlyopen position, premature occlusal contacts are detected and reduced. Progressivrreduction of the height of the central hearing point ant1 sl~~9htspot grinding resultin further refinement of thr occlusal halancc.

These procedures4 are productive of an effective chewing mechanism whichis conducive to a prolonged health of the supporting structures.

Fig. EL-Occlusal view of the finished dentures. The working occlusal surfaces are shownin white, the subocclusal areas in black, and balancing surfaces are shaded,PART II

THE RATIONALEVERTICAL JAW RELATION

The correct vertical relation cannot be ascertained by the consideration ofany one factor. The patients sense of tonic muscle balance and free-way spaceis sometimes unreliable, and if it is accepted as the sole criterion, it will oftendictate too short a vertical jaw relation. Satisfactory ridge or mean foundationplane parallelism is frequently unattainable even though it is highly desirable.

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Volume 5Number 3 CUSPLESS CENTRALIZED OCCLUSAL PATTERN 317Increasing the vertical jaw relation to produce the most pleasing and youthfuliacial appearance is often not only futile, but it may be destructive to the undc-r-lying bone. Phonetic tests after the teeth are set will occasionally suggest anerror of judgment. Only by weighing all factors can the most favorable verticalposition of the mandible be assured.

CENTRIC JAW RELATIONEven though, as stated by BOOS, the greatest power point is not always

at the position of the apex of the Gothic arch tracing, the precise centric relationshould be determined as the starting point. Its value as the final destination ofthe chewing cycle is of paramount importance. If the Gothic arch centric relationis not accepted, it may be discovered later, with dismay, that the other functionalor acquired positions were merely misinterpretations. Some application of a tracingis the only sure and demonstrable method qf ascertaining centric relation. Thecentral bearing intraoral tracing appliance, while not infallible, is simple andeffective, if it is used properly. The stability of the bases of the occlusion rimsis enhanced, and fewer variables are present than by most other methods.

THE ARTICULATORIt should be realized that sagittal or other articulator adjustments exert

only an infinitesimal influence on the limited occlusal paths. These translatoryexcursions are entirely nonfunctional as shown by Boswell and Kurth. Articu-lator reproduction of the functional chewing cycles is manifestly impossible, andhas not even been attempted. The mounting of casts in orientation with the hingeaxis certainly can be of no value in the development of a cuspless occlusion incomplete dentures. Craddock and Symmons have shown that errors obviatedby use of the face-bow cannot be detected clinically. There can be no objectionto such procedures, however, as they constitute an innocuous pastime for thedentist.

POSTERIOR TEETH AND OCCLUSIONBoucher has stated that research should be done to find out, not to prove.

There has been, as yet, no valid, large-scale research Lmdertaken to establish therelative merit of various tooth forms. Commendable projects, such as inaugurated1)~ Paynell and Trapozzano and Lazzari,l should be carried on and greatly ex-panded. The effect of various tooth forms on residual tissues should receiveforemost consideration. Until this is accomplished, clinical observation, experience,and logic must serve as guides. All physical laws and logic favor the acceptanceof the cuspless, centralized, nonanatomic concept of occlusion. It is just too muchto expect of the mucosa, which is trapped between the denture base and the bone,to withstand the clash of the humps and bumps of cusped occlusion. The finaland irrefutable argument in favor of cuspless occlusion lies in the question : Whathappens when inevitable resorptive bone change, however slight, occurs? Cananyone deny that cusped teeth must then contact on the inclines of the cuspswith the resultant diversion of vertical forces into traumatic horizontal forces.

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318 PORTERIf no cusps are present, no harm will result and the greatest power point GU~[be utilized freely without much loss of chewing efficiency.

Final spot grinding and equilibration in the mouth, using centralized pressure,compensates for undetectable variances in yielding tissues in a manner otherwiseimpossible. A minimum of grinding should be done, and the basic occlusal patternmust be preserved. Thus, it is possible to develop a better bilateral and pro-trusive balance than by the use of any adjustable articulator. This occlusal haf--ante, while probably not of great functional value, is nevertheless highly importantin all nonmasticatory closures. This is especially true during neurologic excursions,as described by Shanahan. Even though the value of balancing ramps has heenquestioned by KurthI and others, Yurkstas and Emerson have demonstratedthat they do make contact during mastication.

SUMMARYWhile the case in favor of the cuspless centralized occlusal pattern has not

yet been proved by the eye witness of research, circumstantial evidence stronglypoints to both the ineffectiveness and destructiveness of the anatomic type 4occlusion. Many dentists are following the lead of such thinkers as Sears, Hardy,DeVan, French, Jones, Kurth, Moses, and Pleasure in the procession away iron7the imitators of the cusp-studded anatomic curve of Spee. The feasibility of thecuspless centralized occlusal pattern should be more carefully explored andevaluated. REFERENCES1. Pleasure, M. A.: Correct Vertical Dimension and Free-way Space, J.A.D.A. 43:160-163,1951.2. Sears, V. H.: The Need for Basic Principles in Denture Construction, J.A.D.A. 41:X%-540, 1950.3. Hardy, I. R.: Technique for the Use of Non-anatomic Acrylic Posterior Teeth, D. Digest48 :562-S& 1942.4. Porter, C. G.: Simplicity Versus Complexity, J. PROS. DEN. 2:723-729, 1952.5. Porter, C. G.: Vertical Relation-The Enigma of Complete Denture Construction, Den-tal Survey 26:806-808, 1950.6. Boos, R. H. : Occlusion From Rest Position, J. PROS. DEN. 2:575-588, 1952.7. Boswell, J. V. : Practical Occlusion in Relation to Complete Dentures, J. PROS. DF.s.1:307-321, 1951.8. Kurth, L. E.: Mandibular Movements in Mastication, J.A.D.A. 29:1769-1790, 1942.9. Craddock, F. W., and Symmons. H. F.: Evaluation of the Facebow, J. PROS. Der;.2:633-642, 1952.10. Boucher, C. 0.: Through the Eyes of the Editor, J. PROS. DEN. 3:443, 1953.11. Payne, S. H. : A Comparative Study of Posterior Occlusion, J. PROS. DEN. 2:661-666,1952.12. Trapozzano, V. R., and Lazzari, J . B.: An Experimental Study of the Testing ofOcclusal Patterns on the Same Denture Bases, J. PROS. DEN. 2:440-457, 1952.13. Shanahan, T. E. J.:1953. Physiologic and Neurologic Occlusion, J. PROS. DEN. 3:632-632.14. Kurth, L. E.: Personal communication.15. Yurkstas, A. A., and Emerson, W. H.: A Study of Tooth Contact During MasticationWith Artificial Dentures, J. PROS. DEN. 4:X8-174, 19.54.

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