Articulo Dr. Dawson (1)

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N e w d e f i n i ti o n f o r r e l a t in g o c c l u s i o n t o v a r y i n g c o n d i t i o n s o ft h e t e m p o r o m a n d i b u l a r j o i n t

P e t e r E . D a w s o n , D D S aCenter For Advanced Dental Study, St. Petersburg, Fla.C e n t r i c r e l a t i o n i s t h e a c c e p t e d t e r m f o r d e f i n i n g t h e c o n d y l a r a x i s p o s i t i o n o f i n t a ct ,c o m p l e t e l y s e a te d , p r o p e r l y a l i g n e d c o n d y l e - d i s k a s s e m b l i e s . H o w e v e r , s o m e s t r u ct u r-a l l y d e f o r m e d t e m p o r o m a n d i b u l a r j o i n t s m a y f u n c t i o n c o m f o r t a b ly , e v e n t h o u g h t h e yd o n o t f u l f i ll th e r e q u i r e m e n t s f o r c e nt r i c r e l a ti o n . A w i d e r a n g e o f te m p o r o m a n d i b u -l a r d i s or d e r s f r o m p a r t ia l t o c o m p l e t e d i s k d e r a n g e m e n t s w i t h o r w i t h o u t r e d u c t i o nm a y a d a p t t o a c o n f o r m a t i o n t h a t p e r m i t s t h e jo i n t s t o c o m f o r t a b l y a c c e p t m a x i m a lc o m p r e s s i v e l o a d i n g b y t h e e l e v a to r m u s c l e s . T h e r e h a s b e e n n o a c c e p t e d t e r m i n o l o g yt o d e f in e t h e c o n d i t io n o r p o s i t i o n o f s u c h jo in t s . Th e p u r p o s e o f t h i s a r t i c l e i s tod e f i n e a n e w t e r m , a d a p t e d c e n t r i c p o s t u r e, a n d t o e x p l a i n i t s ra t i o n a l e a n d h o w i t isd e t e r m i n e d . V e r i f i c a ti o n o f s u c c e s s f u l a d a p t a t i o n i s a n i m p o r t a n t s t e p i n d i a g n o s i s,b e c a u s e i t r u le s o u t s t r u c t u r a l in t r a c a p s u la r d i s o r d e r s a s a s o u r c e o f o r o f a c ia l p a ina n d e s t a b l i s h e s r e s p o n s i b l e g u i d e l i n e s f o r i n i t i a t i o n o f o c c l u s a l t r e a t m e n t o r p r o s t h e t i cd e n t i s tr y . I t al s o e s t a b l i s h e s a m u c h n e e d e d t e r m i n o l o g y f o r m o r e s p e c i f i c d e s c r i p t i o no f t e m p o r o m a n d i b u l a r j o i n t p o s i t i o n a n d c o n d i t i o n f o r c l i n i c a l r es e a r c h o n t h er e la t io n s h ip b e t w e e n o c c lu s i o n a n d t h e t e m p o r o ma n d ib u la r j o in t s . ( J PROSTHET DENT1995;74:619-27.)

Confusion about the relationship between dentalocclusion and the temporomandibula r joints (TMJs) hasbeen evident in the literature for many years. Manyauthors advocate that condyle position is critical to theequilibrium of the ma sticatory system at maximal inter-cuspationYTM Others have argued that little or no rela-tionship exists between faulty occlusion and temporoman-dibula r disorders. 2~

In c ontrast to published information that occlusion is nota factor in temporoman dibu lar disorders (TMDs), a reviewof the literature suggests that such a conclusion is not to-tally supported, because the information is routinelydevoid of specific details about the position or the conditionof the temporomandibular joints in relation to occlusalcontacts.20-2t F urt her confusion results from the u se o f thesingle ter m "TMD" to denote a whole constellation of signsor s ymptoms with no specificity of the type of intracapsu-lar deformation or whethe r any s tructural deformation haseven occurred.

It is important to determine the type of intracapsulardeformation or change in TMJ structu res before attempt-ing to determine the optimal relationship between thetemporomandibularjoints and maximal intercuspation ofthe teeth. B ecause the position of the condylar axis can be

aDirector.Copyright 9 1995 by The Editorial Council of THE JOU~AL OVPROSTHETIC DENTISTRY.0022-3913/95/$5.00 + 0. 10/1/67765

altered by these changes , this article att empt s to clarify therationale for positioning healthy condyle-disk assembliesin centric relation and suggests more definitive terminol-ogy and rationale for positioning temporomandibularjointsthat have undergone intracapsular deformation and struc-tural change.

This article suggests three categories for condyle-fossarelationships: centric relation, adapted centric posture,and treatment position. These categories will be defined,explained, and related to maximal intercuspation of theteeth.C E N T R I C R E L A T I O N

Centric relation is defined in this article as the preciselocation of the horizontal condylar axis when properlyaligned condyle-disk assemblies are completely seated intheir respective bony sockets. Because the position of thehorizontal condylar axis determines the maxillo-mandib-ular relationship during jaw closure, any variation incondyla r position will change the closing arc of the mandi-ble and th us affect the initial contact of the mandibularteeth against the maxillary teeth. If maximal intercuspaltooth con tact is not coincident with the completely seatedposition of both condyles, the condyles mus t be displacedto achieve complete jaw closure into maximal intercuspa-tion. Numerou s electromyographic studies reported thatocclusal interferences to centric relation disrupt the coor-dination of mas ticato ry muscle function. 25-3~

The most important criterion for centric relation is the

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Fig. 1. In coordinated muscle function, triad of strong el-evator muscles pulls condyles up slippery posterior slopesof eminentiae. Inferior lateral pterygoid muscles releaseand stay released th rough complete closure if no occlusalinterferences to centric relation occur.

complete release of the lateral pterygoid muscles duringjaw closure. 2 During jaw closure in intact TMJs thecondyle-disk assemblies are pulled up t he eminent iae by atriad of stro ng elevato r muscles (Fig. 1). To ensure a coor-dinated ne uromus culatu re function, the release of inferiorlateral pterygoid muscle contraction must allow thecondyles to slide up to the apex of force positions,n~ at whichpoint th e medial pole of each condyle-disk assemble wouldbe stopped by bone. This buttressed bone stop occurs atthe height of concavity in the medial thir d of each fossa(Fig. 2). This relationship would then be considered theideally aligned or completely seated condyle-disk assem-bly.

The condyles mus t be free to move down and up the pos-terior slope of the eminence during function. The functionof the massete r and internal pterygoid muscles shouldkeep th e condyles loaded 2 against the eminentiae in allexcursive movements (Fig. 3) and in centric relation. Fol-lowing this philosophy, it may be more descriptive to saythat centric relation is the most superior position that theproperly aligned condyle-disk assemblies can achieveagainst the eminentiae. This position would appear to bephysiologic, because it results mechanically from coordi-nated release function, which completely seats the condyle-disk assemblies if no occlusal inclines interfere. Thesignificance of this uppermost position is that only at thisbone-braced relationship is the coordinated activity of theinferior lateral pterygoid muscles achieved through com-plete closure. Ligament bracin g is not a factor, because thecondyles can be displaced down and back from centric re-lation before the ligaments reach their functional limita-

tions. This "uppermost" position is a departure from theconcept of"most retruded." To equate centric relation withthe "retruded position" is still common in the literature,which, although it may be confusing, is acceptable ifachieved by coordinated masticatory muscles. I t should notbe considered centric relation if the condyles are forcedaway from the eminent iae to a more retruded position thanthe one achieved by the coordinated muscle function. Un-fortunately, in patients under going dental procedures thetechnique of pushing the jaw back to record centric relationis still too prevalent.

The reason we advocate preciseness in l(~cating centricrelation is because of the common clinical observation thateven the most minute deflection from the bone-bracedcondyle position may activate uncoordinat ed contraction ofthe lateral pterygoid muscles in opposition to elevatormuscle contraction. Our observations of this uncoordi-nated muscle activity suggests that it can result in myo-fascial pain i f disrup tive occlusal contact is prolonged. It isreasonably assumed th at prolonged isometric contractionof antagonistic muscles can result in myogenous pain,particularly in the smaller lateral pterygoid muscles,which are at a disadvantage.

The trigger that activates lateral pterygoid contractioncan be inconspicuous. The exquisit e sensitivi ty of peri-odontal and interdenta l proprioceptive sensors can triggerpainful reflex muscle patterns from deflective occlusal in-terferences tha t are easily missed by clinicians who do notrecognize their impor tance or the importance of verifyingthe accuracy ofcentric relation before starting any occlusalcorrection procedures (Fig. 4).

In most, if not all, of he published studies th at downplaythe role of occlusion, no att empt has been reported to pre-cisely locate and verify an acc urate centric relation. If thisverification is not done, any conclusions drawn regardingthe relationship between correct occlusion and properlypositioned temporo mandibul ar joints are highly suspect.

The mandible is in centric relation if four criteria arefulfilled:1. The disk is properly aligned on both condyles.2. The condyle-disk assemblies are at the highest pointpossible against the posterior slopes of the eminentiae.3. The medial pole of each condyle-disk assembly is braced

by bone.4. The inferior lateral pterygoid muscles have releasedtheir contraction and are passive.If all four of these criteria are fulfilled, he althy temporo-

mandibu lar joints in centric relation can accept all of theloading that the elevator muscles can apply, because all ofthe force is directed through avascular, noninnervatedstru ctures tha t were designed to be load-bearing. 3236 If theupwa rd slide of the condyle-disk assemblies is stopped bybone, no resistance should be required from the inferiorlateral pterygoid muscles once the condyles are completelyseated; therefore upward loading should not alter their

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Fi g. 2. The condyle-disk assemblies slide up convex posterior slopes of eminentiae untilmedial poles (solid arrow) are stopped by buttres sed bone at medial third of fossae. Circleindicates upper most position at which medial pole braces aga inst bone (with disk inter-posed). Lat eral two thirds of roof of fossa is thin and n ot beari ng area.

Fig . 3. No muscles are in a position to distr act condyles. Whe the r occlusal contac t is onanterior teeth only or posterior teeth only, all elevator muscles combine to direct thecondyles antero-superiorly in centric relation (A) and also keep th em loaded agai nst em-inentiae as they travel up and down the slopes in function (B).

passive state during closure or activate their contractioneven during strong clenching. So unless the muscles aretriggered by a disruptive occlusal contact that occursbefore maximal closure is complete, the coordinated re-lease of he inferior lateral pterygoid muscle should remainconsistent with elevator muscle contraction during the re-petitive clenching posture associated with swallowing.

When both condyle-disk assemblies are completelyseated in centric relation, their medial poles should be at

the highest point of concavity of that part of each fossa.From where the medial poles are stopped by bone the fos-sae walls curve downward on three sides so that from acorrect centric relation, the condyles cannot travel for-ward, backward, or medially without moving downward(Fig. 5). The un der sta nding of this apex of force position isextremely impor tant to our concept of centric relation. I tmeans tha t failure to completely seat condyles when har -monizing an occlusion invariably results in a muscle-

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Fig. 4. Load testing conducted at suspected centric rela-tion hinge position with torquing action start ing with gen-tle loading first, then increasing pressure from light to veryfirm. Any sign of tension or tend erness in either joint in-dicates that centric relation has not been achieved. Fingersmust be placed on posterior half of mandible duringmanipulation.

braced condyle instead of a bone-braced condyle. It alsomeans t hat wheneve r the condyles go to their more upwardcentric relation position during function, the closing forcesare directed more on the most posterior teeth, whichbecome pivotal to the upward moving condyles (Fig. 6).

Contra ry to some opinions tha t centric relation is not afunctional position, that observation has not been sup-ported by extensive researc h at the University of Florida isor in studies that show that the retruded position is usedfrequently in swallowing. 37 If the idea t hat the condyles dogo repeatedly to centric relation is doubted, it would onlybe necessary to observe the facets of wear on the teeth ofa numb er of patients. Casts mo unted correctly in centricrelation routinely show that if wear facets are present, thefacets always extend to centric relation on tooth inclinesthat interfere with centric relation.

A study of condyle/fossa anatomic condition makes itevident that the medial wall of the fossa braces against themedial pole of he condyle disk assembly when the condylesare in centric relation. This fact is why centric relation isthe midmost position of the mandible (Fig. 7). Thus fromcentric relation it is not possible for eithe r condyle-disk as-sembly to move horizontally toward the midline. I f such amovement occurs, it is an indication t hat the condyles werenot completely seated in centric relation at the start ofmovement. From centric relation the orbiting condylemust move downward as it moves medially.

A D A P T E D C E N T R I C P O S T U R EMany TMJs function with complete comfort and appar-

ent normalcy, even though they have undergone deforma-tion caused by disease, trauma, or remodeling and there-fore automatically c annot fulfill all of our criteria for cen-tric relation. Some TMJs click or exhibit other signs ofintracapsular disorder, but they do not prevent patientsfrom functioning in an acceptable and comfortable man-ner. Determining whether a deformed TMJ can functionacceptably with comfort and with a reasonable degree ofstability is one of the m ost impo rtant decisions in the di-agnostic process.

The author defines adapted centric posture as the rela-tionship of the mandible to the maxilla that is achievedwhen deformed temporom andibular joints have adapted tothe degree that they can comfortably accept firm loadingwhen completely seated at the most superior positionagainst the eminentiae.

Like centric relation, adap ted centric posture is a hori-zontal axial position of the condyles. It occurs irrespectiveof vertical dimension or toot h contact. It is also a midmostposition, because even if the disk is totally displaced, themedial pole of the condyle adapts to the concavity of thefossa and maintains contact against its medial incline.

The mandible is in adapted centric posture if four crite-ria are fulfilled:1. The condyles are comfortably seated at the highestpoint against the eminentiae.2. The medial pole of each condyle is braced by bone. (Thedisk may be partially interposed.)3. The inferior lateral pterygoid muscles have released

contraction and are passive.4. The condyle-to-fossa relationships occur at a manage-able level of stability.The consequences of adaptive changes in the temporo-

mandi bular articulation may be positive or negative withregard to symptoms. The same adaptive changes that re-sult in reduction of symptoms may simult aneously produceserious and progressive deformation ofintracap sular struc-tures and dama ge to collateral structures eleswhere. Teethand supporting structures can be especially affected bystruc tural changes of the TMJs. We note that excessiveocclusal wear or hypermobility of teeth is routinely ob-served as disharmony between the TMJs and the occlusionprogresses. 3s Our clinical observation is consistent: unsta-ble TMJs result in unstable occlusions.

Adapted centric posture m ay be achieved in a variety ofintracapsular deformations. The progression from ahealthy, intact TMJ to one that is deformed and hasadapted may include stages that produce pain and dys-function as the adaptation process takes place. The pro-gression of deformation ma y occur with little or no intra-capsular pain. Diagnosis made on the basis of symptomsonly is insufficient and may lead to false assumptionsabout the source of pain in patients with TMD.

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Fig. 5. Medial pole of each condyle-disk assembly is braced against uppermo st roof ofconcavity at medial third of each fossa. From t hat seated position condyles cannot moveforward, backward, or medialward without t raveling downward (circle represents medialpole position). Because an terio r face of each condyle disk assembl y ( l ine wi th three arrows)is against eminence in centric relation, no forward translat ion is possible without down-ward movement.

Proper diagnosis requires an orderly evaluation ofintra-capsular struct ures, not jus t to see wheth er deformation ispresent but to determine t he specific stage of deformationresponsible for the discomfort. The clinical experience ofthe author has shown that in most patients with so-calledTMD, the discomfort is far more likely to be myogenousrather than intracapsular, even when some deformationhas occurred within the intracapsular structures. This di-agnosis cannot be determin ed on the basis ofepidemiologicpercentages. It must be determined by specific testing ofeach individual patient to determine whether any intrac-apsula r stru ctures are disordered, and, if they are de-formed, to determine whether they have adapted to amanageab le level of comfort and stability. A combinationof history, load testing, auscultation, and palpation canusually lead to a diagnosis, but some type of imaging ma ybe needed for specificity.

Some of the most common intracap sular conditions thatmay permi t an a dapted centric posture are (1) lateral poledisk derangements , (2) complete disk derangements withformation of a pseudo-disk, (3) complete disk displacementwith perforation, and (4) other partial disk derangementsand asymptomatic clicking TMJs.L a t er a l p o l e d i s k d e r a n g e m e n t s

Piper's classification of intra capsul ar disorders distin-gnishes between lateral pole disk derangements andderang ement s in which the disk is displaced off both thelateral and medial poles of the condyle. If the disk is not

displaced off the medial pole, it is possible to achieve com-plete seating ofthe condyle with no discomfort. This is trueeven when a lateral pole click has progressed to closed lockof the lateral half of the disk. I f the intraca psular defor-mation is intercepted at these stages, it has been our clin-ical experience that stability of the articulation can beachieved if harmon y is established be tween the occlusionand the completely seated condyle-disk assemblies.

The experience of the author also suggests that lateralpole disk derang ements can be treated as normal joints ifthe medial pole disk alignment is acceptable and if adaptedcentric posture can be veri fied by load tes ting. 39 In my ex-perience the key to success is in main taini ng coordinatedmusculature function through elimination of all occlusalinterferences to a verified adapted centric posture.C o m p l e t e d i sk d e r a n g e m e n t s w i t h f o r m a t i o no f a p s e u d o d i s kIn the early stages of a complete disk displacement it isthe experience of the a uthor tha t a period exists duringwhich pain is a symptom. Considerable pain may resultfrom compression of the vascular and richly innervatedretrodiskal tissue by the condyle (Fig. 8). If this compres-sion occurs, adapted centric posture cannot be achievedbecause the TMJ will not accept loading without some de-gree of discomfort. Although not predictable, the retrodis-kal tissue is sometimes converted to a fibrous connectivetissue pseudo-disk. We have observed such pseudo-diskformation in cadaver specimens, in open-joint microsur-

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, ~ l [ [ / [ [ i l F i g . 7 . M e d i a l p o l e b r a c i n g in l i n e w i t h m e d i a l p t e r y g o i dt i i[IIr m u s c l e c o n t r a c ti o n e s t a b l i sh e s midmosto s i t i o n a t c e n t r i c: ~ ~ ~ ~ re la tio n. T hi s m i dm o st p os i t i o n is c on si s te nt ly s m u lt a-' n e o u s w i t h u p p e r m o s t p o s it io n .

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F i g . 6 . B e c a u s e c o nd y le s m u s t d i sp l ac e d o w n w a r d t o a c- ~ xc o m m o d a t e i n t e r c u s p a l p o s i ti o n t h a t i s f o r w a r d o f c e n t ri cr e l a t io n ( A ), m o s t p o s t e r i o r t o o t h t h a t i n t e r f e re s b e c o m e sp i v o t a l p o i n t w h e n c o n d y l e s a r e p u l l e d u p i n t o c e n t r i c r e - F i g . 8 . I n e a r l y s t a g e s o f c o m p l e t e d i s k d e r a n g e m e n t ,l a t io n . B , I n f e r i o r l a t e r a l p t e r y g o i d m u s t r e m a i n a c t i v e l y c o n d y l e l o a d s o n t o v a s c u l a r , r e t r o d i s k a l t i s s u e , w h i c h i sc o n t r a c t ed w h e n e v e r t e e t h a r e i n t e r c u s p a te d , r i c h ly i n n e r v a t e d . W h e n t h i s s t r u c t u r a l m i s a l i g n m e n t o c-

c u r s, T M J c a n n o t a c c e p t l o a d i n g w i t h o u t p a i n .g e r y , a n d o n m a g n e t i c r e s o n a n c e i m a g e s . I f t h i s f o r m a t i o no c c u r s, i t i s p o s s i b l e t h a t b l o o d v e s s e l s a n d t h e i r a c c o m p a -n y i n g s e n s o r y n e r v e s w i ll e v a c u a t e t h e b e a r i n g a r e a , a n dt h e f i b r o u s e x t e n s i o n o f t h e o r i g i n a l d i s k w i ll e v e n t u a l l y b ea b l e t o a c c ep t l o a d i n g w i t h n o d i s c o m f o rt . I t m a y t h e n b ep o s s ib l e t o a c h i e v e a n a d a p t e d c e n t ri c p o s t u r e t h a t a p p e a r st o b e a s s t a b l e a s a n i n t a c t c o n d y l e - d i s k a l i g n m e n t .C o m p l e t e d is k d i s p l a c e m e n t w i t h p e r f o r a t io n

T h e m o s t l i k e l y p r o g r e s s i o n f r o m a c l o se d - lo c k , a n t e r i o rd i s p l a c e m e n t o f t h e d i s k i s to p r o c e e d t h r o u g h a p a i n f u ls t a g e o f c o m p r e s s i o n o f t h e r e t r o d i s k a l t i s s u e s , w h i c h b e -c o m e l e s s p a i n f u l a s t h e c o n d y l e p e r f o r a t e s t h e s e n s i t i v e

v a s c u l a r t i s su e s a n d b e g i n s t o l o ad a g a i n s t b o n e . A s t h es o f t - t i s s u e p e r f o r a t i o n e x p a n d s , a c o m p l e t e b o n e - t o - b o n ec o n t a c t m a y r e s u l t t h a t p e r m i t s l o a d i n g w i t h n o i m p i n g e -m e n t a g a i n s t i n n e r v a t e d s t r u c tu r e s . A t t h i s s t a g e i t is p os -s i b le t o v e r i f y a n a d a p t e d c e n t ri c p o s t u r e b y t h e a b s e n c e o fd i s c o m f o r t w h e n t h e c o n d y l e s a r e l o a d e d .

T h e t y p i c a l s e q u e n c e o f e v e n t s t h a t w e h a v e e x p e r i e n c e da f t e r t h e r e t r o d i s k a l t i s s u e i s p e r f o r a t e d i s a p r o g r e s s i v ef l a t t e n i n g o f b o t h t h e c o n d y l e a n d e m i n e n c e . T h e o s t e o a r -t h r i t i c d e f o r m a t i o n s t a r t s a t t h e a r t i c u l a r c a r t i l a g e , c a u s-i n g a l o s s o f h e i g h t o f t h e c o n d y le . B e c a u s e t h e p e r f o r a t i o n

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and disk dera ngeme nt d isrupts the flow of synovial fluid,nourishment to the articular surfaces is compromised.Thus the osteoarthritic joint is not completely stable.Although the condyle will continue to lose height as itsbearing surface breaks down, the deformation can usuallybe slowed to a manage able condition by reestablishing co-ordinated muscle function and reducing muscle hyperac-tivity. Any discomfort in this type of problem is invariablymyogenous. It can be readily resolved by restoring har-mony between the occlusion and the completely seatedTMJs, even though they have undergone deformation.

It is the author's contention that patients with slowlyprogressing osteoarthritis can be made as comfortable aspatients with intact TMJs if occlusal harmony is estab-lished with adapted centric posture. If both condyles canaccept loading with no discomfort, relief of myofascial painis highly predictable if all occlusal interferences to thebone-braced condyle position are completely eliminated.Typically, it is necessary to adjust the occlusion periodi-cally as condylar height is lost, but it does not create aman agem ent problem if patients are informed of this needin advance. In my clinical experience minimal correctionsto the occlusion are all t hat is needed at 9- to 12-month in-tervals to maintain comfort in the masticatory muscula-ture.O t h e r p a r t i a l d i s k d e r a n g e m e n t s a n da s y m p t o m a t i c c l i c k i n g T M J s

Reciprocal clicking is a sign that some degree of defor-mation has occurred in the diskal ligaments. The varia-tions in deformation of the ligaments and the disk appearunlimited. However, many clicking and deformed jointshave a dapted sufficiently so that they can comfortably ac-cept loading. If a structur al analysis shows that the condi-tion is reasonably stable, adapted centric posture may beachieved, even though the disk is deranged and a click ispresent. The key to successful treatm ent of adapted TMJsis the complete seating of both condyles so that the inferiorlateral pterygoid muscles can release their contractionduring closure all the way to maximal intercuspation.T R E A T ME N T P O S I T I O N

Three general types ofintr acapsular disorders result inpain or discomfort when the temporo mandibul ar joints areloaded.1. In complete displacement of he disk, disk displacementis almost always anterior to the condyle, which resultsin compression of the vascular, innervated, ret rodiskalstructures. If the disk is not reducible and compressionofretrodi skal tissue causes discomfort, it is necessary todetermine a tre atment position for the condyle for thepurpose of developing an adapted centric posture thatcan even tually acce pt loading.2. Retrodiskal inflammation and ede ma usually occurs asa result of trau ma and ma y or may not be associated

with disk displacement. When the retrodiskal tissuesare swollen and painful, t he condyles cannot completelyseat to either centric relation or adapted centric posturewithout compressing these structures. A treatme nt po-sition that reduces the compressive force and allows theinflamma tion to subside should be determined. Antiin-flammatory medication and soft diet are recommendedin combination with the use of a trea tme nt position thatis protruded enough to prevent compression of retro-diskal tissue. The condyles should be permitted toretu rn to centric relation or adapted centric posture assoon as the edema is reduced, which is usually a mat-ter of a few days.3. Pathologic conditions and struc tural or functional dis-orders that affect the ability of the int racaps ular struc-tures to accept loading can result from a variety ofcauses. The basic rule is, "If the TMJs ca nnot acceptloading with complete comfort...find out why."

Differential diagnosis must first confirm tha t the sourceof pain is within the i ntraca psular structure s an d not iso-lated i n muscle. Load testing is the most effective way tomake that determination. Masticatory muscle pain iscommon when int racapsu lar pathosis is present, becausethe muscles tend to protect the painful joint from overload.Attemp ting to treat mastica tory muscle problems withoutknowledge of the specific type of intracaps ular problem isinappropriate. Appropriate treatment combines an at-tempt to resolve the intra capsul ar problem while simulta-neously establishing equilibrium within the total mastica-tory system. If this procedure requires harmonization ofthe occlusion with a t empor ary trea tmen t position for thejoints, that decision should be based on determining theoptimal treatment position first.Not all pathologic deformation results in pain on loading.It is sometimes possible to load condyles with advancedbone disease, but the condition may be too unstable towarrant treatment procedures that are irreversible. Acomplete diagnosis including history, palpation, load test-ing, Doppler auscultation, range and path of motion test-ing, and appropriate imaging should be used to determinea specific diagnosis. 2, 39 Blood studies, surgical exploration,or both may be needed in some cases. It is not the purposeof this article to outline all the protocols for diagnos ing thewide range of diseases tha t may be encountered. Advance-ments in diagnostic tests and imaging capabilities make itdifficult for structural disorders to hide from an astute di-agnostician.D e t e r m i n a t i o n o f t r e a t m e n t p o s i t i o n

The need for a trea tmen t position can be determined af-ter it has been verified that neither centric relation oradapted centric posture can be achieved. Two objectivesexist in determining the most favorable trea tmen t positionfor the condyles: (1) relief of pain, and (2) eventual stabi-lization of he condyles in either centric relation or adaptedcentric posture.

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I t m a y b e d i f fi c u l t t o d e t e r m i n e w h e t h e r a t r e a t m e n t p o -s i t i o n is n e c e s s a r y i f l a t e r a l p t e r y g o i d m u s c l e c o n t r a c t i o ni s n o t r e l e a s e d . T h e p a i n o f m u s c l e s p a s m o r p r o l o n g e d h y -p e r c o n t r a c t i o n m a y m a k e i t t o o d i f f i cu l t t o a c h i e v e co m -f o r t a b l e s e a t i n g o f t h e c o n d y l e s , e v e n w h e n n o i n t r a c a p s u -l a r d i s o r d e r is p r e s e n t . U n l e s s a n a c t i v e i n t r a c a p s u l a r d i s-o r d e r is o b v i o u s, a n a t t e m p t s h o u l d b e m a d e t o d e p r o g r a ml a t e r a l p t e r y g o i d c o n t r a c t i o n b e fo r e a s s u m i n g t h a t t h eT M J s a r e t h e p r i n c i p a l s o u r c e o f t h e p a i n . I t i s s u g g e s t e dt h a t t h i s d e p r o g r a m m i n g i s b e s t d o n e b y c o m p l e t e l y se p -a r a t i n g a l l p o s t e r i o r t o o t h c o n t a c t b y u s i n g a s m o o t h , f l a t,a n t e r i o r b i t e p l a n e . S u c h a p e r m i s s i v e s p l i n t a ll o w s t h em u s c l e s t o m o v e t h e m a n d i b l e i n c o o r d in a t e d f u n c t io n t h a ti s u n d i s t u r b e d b y d e f l ec t i v e t o o t h c o n t a c t s . I f t h e p e r m i s -s i v e s p l i n t p e r m i t s r e l e a s e o f l a t e r a l p t e r y g o i d m u s c l e c o n -t r a c t i o n a n d a l l o w s t h e c o m p l e t e s e a t i n g o f t h e c o n d y l e s t oc e n t r i c r e l a t i o n o r a d a p t e d c e n t r i c p o s t u re , u s e o f a t r e a t -m e n t p o s i t i o n w i l l n o t b e n e c e s s a r y . T h e r e l i e f o f o c cl u so -m u s c l e p a i n o c c u r s q u ic k l y , m o s t o f t e n w i t h i n h o u r s w h e na l l o c c l u s al i n t e r f e r e n c e s a r e e l i m i n a t e d . I f t h e p e r m i s s i v es p l i n t d o e s n o t r e s u l t i n r e l i e f o f a l l d is c o m f o r t w h e n t h ec o n d y l e s a r e l o a d - t e s t e d , a n i n t r a c a p s u l a r d i s o r d e r is s u s -p e c t e d , a n d f u r t h e r t e s t i n g i s i n o rd e r t o d e t e r m i n e w i t hs p e c i fi c i t y t h e t y p e o f s t r u c t u r a l d i s o r d e r t h a t i s p r e s e n t .T h e t r e a t m e n t p o s i t i o n t h a t i s s e l e ct e d s h o u l d b e s p e ci f i cf o r t h e t y p e o f d i s o r d e r t h a t i s d i a g n o s e d .

S U M M A R YL a c k o f d e f i n i t i v e t e r m i n o l o g y t o c l a r if y d i f f e r e n t p o s i-

t i o n s a n d c o n d i t i o n s o f t h e t e m p o r o m a n d i b u l a r j o i n t s h a sc a u s e d c o n f u s i o n i n t h e l i t e r a t u r e a n d h a s c o m p l i c a t e ds c i e nt i fi c d i s c u s s i o n r e g a r d i n g t h e r e l a t i o n s h i p o f t h eT M J s t o o c c l u s i o n .

U s e o f t h e n o n s p e c i f i c t e r m T M D i s in a d e q u a t e f o rd e s c r i b i n g s p e c i fi c d i s o r d e r s o f t h e m a s t i c a t o r y s y s t e m .T h e t e r m T M D d o e s n o t s pe c i fy w h e t h e r a d is o r d e ri n v o l v e s d e f o r m a t i o n o f i n t r a c a p s u l a r s t r u c t u r e s , d o e s n o ts p e c if y w h e t h e r a d i s o r d e r i s p r i m a r i l y a m a s t i c a t o r ym u s c l e p r o b l e m w i t h o r w i t h o u t i n t r a c a p s u l a r d e f o r m a -t io n , d o e s n o t s p e ci f y w h e t h e r a d e f o r m e d T M J h a s a d a p t e ds u f f i c ie n t l y to a c c e p t l o a d i n g w i t h o u t d i s c o m f o r t , d o e s n o ts p e c if y w h e t h e r a n a d a p t e d T M J i s s t a b l e or u n s t a b l e , a n dd o e s n o t s p e c i fy t h e t y p e o f d e f o r m a t i o n o r p a t h o s i s w i t he n o u g h c l a r i t y to b e m e a n i n g f u l i n d e t e r m i n i n g a n o p t i m a lt r e a t m e n t p o s i t i o n f o r T M J s t h a t c a n n o t a c c e p t l o a d in g .

I t is t h e a u t h o r ' s b e l i e f t h a t u n c o o r d i n a t e d , h y p e r a c t i v e ,m a s t i c a t o r y m u s c l e s a r e t h e p r i m a r y s o u r c e o f r e p e t i t iv e ,t e n s i v e , a n d c o m p r e s s i v e fo r c es a g a i n s t t h e T M J s a n d t h et e e t h a n d o t h e r m a s t i c a t o r y s y s t e m s t r u c t u r e s . I t i s t h ea u t h o r ' s b e l i e f t h a t a n a l y s i s o f t h e c a u s e s f o r m a s t i c a t o r ym u s c l e p a i n o r d y s f u n c t i o n m u s t i n c l u d e a c c u r a t e d e s c r i p -t i o n o f t h e r e l a t i o n s h i p o f t h e o c c l u s io n t o t h e p o s i t i o n a n dc o n d i t i o n o f t h e T M J s .

R E F E R E N C E S

1. Rami~ord SP, Ash MM . Occlusion. 4th ed. Phi ladelphia: WB Sau ndersCo, 1983:76.2. Dawson PE. Evahia t ion, diagnosis and t re atm ent of occ]usal problems.2nd ed. St Louis: CV Mosby Co, 1989:28-39.3. Celenza FV, Na sedkin JN. Occlusion, the state of the ar t . Chicago:Quintessen ce Publ ish ing Co Inc, 1978:31-46.4. Gilboe D. Centric rela tion as th e tre at m en t position. J PROSTI-IETDENT1983;50:685-9.5. Wil l iamson EH . Larainographic study o f ma ndibu lar condyle posi tionwh en reco rding cen tric relation. J PROSTHETDENT 1978;39:561-4.6 . G ibbs CH, L undeen HC, M ahan PE , e t a l . Movemen t s o f t he m ola rteeth a nd m and ibula r condyles dur ing chewing [Abstract]. J De nt Res1980;59:915.7. Lucia VO. A tec hniq ue for reco rding cen tric relation. J PaOSTKETDENT1964;14:492-505.8. Gra nge r ER. Cen tric relatio n. J PROSTHET DENT 1952;2:160-71.9. O keson JP. Ma nage men t of temp orom andibu lar disorders an d occlu-sion. 3rd ed. St Louis: Mosby-Year Book, 1992:110-1.10. Guiche t NF. Biologic a ws governing unct ions ofmuscles tha t move themand ible. Par t 1: Occlusal programming. J P rosthe t Dent 1977;37:648-56 .Long JH Jr. Locating ce ntric relatio n wi th a lea f gauge. J PROSTHETDENT 1973;29:608-10.Woelfel JB. A new device for accurately recording centric relation. JPROSTHET DENT 19 86;5 6:71 6-27 .McHorr is WH. O cclusal adjustm ent via selective cut t ing of natu ralteeth. Pa r t I . Int J Per iodont Rest Den t 1985;5:8-25.L aur i t zen AG. Func t iona l ana lys i s t echn ique in t h e n a tu r a l den t i ti on :atla s of occlusal analysis. C olorado Springs: HAH Publications, 1974.Schuyler CH. F und am enta l pr inciples in the correct ion of occlusal dis-harmon y, natu ral and ar ti ficial . J Am D ent Assoc 1935;22:1193-202.Lytle JD. The clinicians in dex of occlusal disease: definition, recogni-t ion and man agem ent . Int J P er iodont Rest Dent 1990;10:102-23.Beyron H. Opt im al occlusion. De nt C l in Nor th Am 1969;13:537-54.Lund een HS, Gibbs CH. Advances in occlusion. Boston: Joh n W right ,1982.Man n AW, Pankey L D. Or a l r ehab i li t a t ion . Pa r t I : Use o f t he P - M in -s t r ume n t i n t r ea tm en t p l ann ing and in r es to r ing the l ower pos te r io rtee th. J PROSTHET DENT 1960 ;10:135-5 0.20. Greene CS. Orthodont ics andtem porom andibulardisorde rs. Den t Cl inNor th A m 1988;32:529-38.21. Lipp MJ. Tem porom andibular symp toms and occlusion: a review of hel i terature a nd the concept. N Y State De nt J 1990:56:58-66.22. Dworkin SF, Ha nson Huggins K, Le Resche LH, et al . Epidemiology ofsigns and symp toms in temp orom andibu lar disorders: cl inical signs incases and controls. J Am D ent Assoc 1990;120:273-81.23. Goodman P, G reene CS, Laskin DM. Response of pat iente wi th myo-fasclal pain-dysfunction synd rom e to mock equilibration. J Am D entAssoc 1976;92:755-8.24. Adler RC. W hat do a leech and a han dpiece have in common? J CranioPractice 1993;11:1.25. Ramijord SP. Dysfunctional temporom andibu lar oint and muscle pain.J PROSTHET DENT 1961;11 :353-74.26. Bakk e M, Moller E . Distor tion ofm axim um elevator activity by uni lat -eral tooth contact . Scand J Den t Res 1980;80:67.27. Ri ise C, S heikholeslam A. The inf luence of exper ime ntal inter fer ingocclusal contacts on postural act ivi ty of the anter ior temporal andma ssete r muscles in young adul ts. J O ral Rehabi l 1982;9:419-25.28. Wil l iamson EH, Lund qnist DO. Anter ior guidance: i t s ef fect on elec-t romyographic act ivi ty of the tem poral an d ma ssete r muscles. J PRos-THET DENT 1983;49:816 -23.29 . Hann am AG, DeCow RE , Sco tt JD , Wood WW. T he r e l a t i onsh ipbetwee n denta l occlusion, muscle ac t ivi ty and associated jaw move-me nt in m an. A rch Oral Biol 1977;22:25-32.30. M aha n PE, Wilkinson TM, Gibbs CH, Ma uder l i A, Brannon LS. Supe-r ior and in fer ior bell ies of the latera l pterygoid EM G act ivi ty at b asicjaw posi t ions. J Prosthe t Dent 1983;50:710-8.31. Schae fer P. Stal la rd RE, Zander HA. Occlusal inter ferences and mas-tication: an electrom yograp hic stu dy . J PROSTHET DENT 1967;1 7:438-49 .

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32. Zola A. Morphologic limiting factors in the temp oromandibular oint. JPROSTHET DENT 1963;13:732-40.33. Sicher H. The temporomand ibular oint. In: Sarnot BG, editor. 2nd ed.Springfield, Ill: Charles Thomas Publisher, 1964.34. Mansour RM, Reynik RJ. In vivo occlusal forces and moments: forcesmeasured in t erminal hinge position and associated moments. J DentRes 1975;54:114-20.35. Smi th DM, McLochlan KR, McCall WD. A numerica l model of tem-poromandib ular join t loading. J Dent Res 1986;65:1046-52.36. Hylander WL. The human mandible: leverorlink. Am J Phi p Anthro-pol 1975;43:227-42.37. Gra f H, Zander HA. Tooth contact pat ter ns in mast ication. J PEOSTHETDENT 1963;13:1055-66.

38. Schellhas KP, Piper MA, Omlie MR. Facial skeleton remodel ing due totemporomandibular joint degeneration: an imaging study of 100patient s. Am J Neuroradiol 1990;11:541-51.39. Dawson PE, Pipe r MA. Temporomand ibula r disorders and orofacialpain. Seminar Manual. St Petersburg: Center for Advanced DentalStudy, 1993:130-45.Reprint requests to:DR. PETER E. DAWSON1 1 1 SECONDAVE., NESurrE 1109ST. PETERSBURG, FL 33701

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