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Newly described muscle attachments to the anterior band of the articular disk of the temporomandibular joint
JA D )A A R T I C L E S
This article describes the accidental discovery of additional muscle attachments to the temporomandibular join t articular disk. Previously, only one muscle attachment has been reported in the literature. This discovery may provide valuable information for the clinician treating temporomandibular disorders.
Newly described muscle attachments to the anterior band of the articular disk of the temporomandibular joint L. J. Myers, DDS
n til this tim e, only one m uscle h as been k n o w n to a tta c h to the a rtic u la r disk of th e te m p o ro m an d ib u lar jo in t (TM J). T h is was the superior head of the lateral pterygoid m uscle that acted to m aintain the position of the disk on the condyle w hile closing. T h e o n ly la te r a l a tta c h m e n t w as th e lateral collateral ligam ent th a t attached the disk to the lateral pole of the condyle of the m andible. T h is lack of ligam ent a n d m u scle a tta c h m e n t has seem in g ly c o m p ro m ise d th e “ p e r m a n e n t” r e p a ir of the disk-condyle system after displace m e n t of th e d isk a n d th e c o n s e q u e n t s tr e tc h in g o r te a r in g o f th e la te r a l c o lla te r a l lig a m e n t a n d s tr e tc h in g of th e p o ste rio r elastic la m in a a tta c h in g th e d isk to th e p e tro ty m p a n ic fissu re of the skull. A lth o u g h successful re p o sitio n in g of the disk o n the condyle is now com m on place, this has been th o u g h t of as m ore of a “ tem porary” success as the dam age already done in the displacem ent makes the disk highly unstable. T heoretically, rep air an d reposition w ould need to be re p e a te d . R e la p se of p ro p e rly tre a te d disk displacem ents has, however, proved to be the exception rather th an the rule. T h e puzzle is pieced by the understanding of new muscles described in this article. T h e presence of previously u n rep o rted muscles w ould explain why repositioning
U
the disk on the condyle is m ore successful th a n w ould be expected. Methods and materials
T h e se m uscles w ere fo u n d by accident d u rin g a tedious p ro ced u re th a t is not
o ften p erfo rm e d o n th e d eep m asseter m uscle. A previous dissection h ad been perform ed, freeing the disk to study the retrodiskal tissues by sectioning the skull vertically th ro u g h the external auditory canal. T h e m asseter m uscle fibers were b e in g dissected a n d c h a rte d fo r vector
F ig 1 ■ N ew ly described m u scle attachm ents to the anterior band o f the articular disk o f the tem p orom andib ular jo in t in m ale specim ens. Key: 1 = head of con d yle, 2 = zygom a, 3 = deep m asseter m u scle, 4 = zygo m a tico d isk a l m u scle (n ew ), 5 = m an d ib u lar d isk a l m u sc le (n ew ), 6 = anterior band of articular disk, and 7 = superior head of lateral pterygoid muscle.
JADA, Vol. 117, September 1988 ■ 437
A R T I C L E S
analysis. After reaching the deepest fibers of this m uscle an d detaching them from the zygom atic process (and in this case th e la te r a l su rfa c e of th e a r tic u la r ca p su le ),1 6 it was seen th a t there were d e e p e r fib e rs th a t w ere a tta c h e d in com m on w ith deep m asseter m uscle fibers ju st below the m a n d ib u la r notch on the la te r a l su rfa c e of th e m a n d ib le . T h e d irectio n of the fibers was n o t p arallel to the deep masseter fibers, b u t deviated posteriorly 30°. W h e n te n s io n w as a p p lie d to these fib e rs, th e a r ti c u la r d isk , w h ic h w as prev io u sly loosened, was seen to m ove fo rw ard . T o m o re closely observe the attachm ent, the zygom atic arch was cut w ith a reciprocal saw at its anterior end an d ag a in in a m edio an terio r direction above th e condyle to av o id d is ru p tin g th e a n te r io r b a n d of th e disk w ith its attachm ents. After everting the zygomatic arch , a second set of fibers w as found in th e in n e r su rfa ce o f th e zygo m atic arch, a n d in se rtin g on the m iddle p art of th e a n te r io r b a n d of the disk. T h e fib ers o r ig in a tin g o n th e m a n d ib u la r no tch inserted laterally to this but were still o n the anterior p o rtio n of the anterior band. At th a t tim e, kn o w in g there were no reported muscles w ith these origins and in se rtio n s, the h ead of the d ep a rtm en t of anatom y was called to see the discovery. H e dissected the m a n d ib u la r head free of its fibers to its insertion a n d origin, an d suggested that p h o to g rap h s be taken an d o th e r heads exam ined in the same way to determ ine if this was an anom aly. C u rre n tly , d iss e c tio n s h av e b een p e r form ed on 14 other adults, one full-term fetus, a n d one M acaca m onkey. In all specim ens, these muscles have been found alth o u g h they have varied in size in the d ifferen t specim ens. T h e re seems to be a gender difference w ith the female not as w ell d e v e lo p e d , b u t w ith so few specim ens it cannot be deem ed universal. T h e fetus was m ale a n d the tw o muscles were w ell differentiated. In the monkey, th e m uscles w ere p rese n t ag a in . In all cases, the m an d ib u la r diskal muscle was s e p a ra te fro m th e p o s te rio r b o rd e r of the tem poralis m uscle w ith the masseteric nerve p a s sin g betw een th e tw o m asses of m u sc le fib ers. In o ld e r sp e cim en s, the zygom aticodiskal m uscle showed an increase in fibrous tissue w ith consequent loss of m uscle fibers. T h is same finding was n o t seen in the m a n d ib u la r diskal m uscle (Fig 1, 2). In later dissections it was found that the best way to show these muscles was 438 ■ JADA, Vol. 117, September 1988
Fig 2 ■ Photographs, top left and right, and bottom left, show new ly described m uscle attachments in female specim ens. Bottom right show s same in male fetus (Key: same as in Fig 1).
to remove the jo in t ap p aratu s com pletely as follows. W ith the b rain rem oved and the head sectioned sagittally, the vertical cut is m ade w ith a reciprocal saw through the external auditory canal. T h is leaves o n ly a sm a ll se c tio n o f th e ty m p a n ic plate b ehind the T M J. In m ost specim ens, th is is easily rem oved a t the p etro ty m p a n ic fissure. T h is exposes the cran ial a tta c h m e n t of the su p e rio r retro d isk a l lam ina. T h e superficial lam in ae of the m a sseter m u scle are rem o v ed , le a v in g on ly the deep lam in ae. T h e zygom atic a rc h is th e n c u t v e rtic a lly in fro n t of the zygom aticotem poral suture and again at a 45° ang le postero an terio rly ju s t in front of the lateral pole of the condyle, le a v in g th e o r ig in o f th e r e m a in in g m a sse te r in ta c t. T h is o p e n s u p th e coro n o id process th a t is then cu t h o ri zontally for the rem oval of the tem poralis m uscle. T h e tem poralis m uscle is then rem oved by d issection a t th e o rig in at th e side of th e sk u ll. W ith b lu n t d is section, the tem poralis m uscle is removed w ith th e c u t p o r tio n of th e c o ro n o id pro ce ss. T h is o p e n s u p th e la te ra l pterygoid muscle, w hich is carefully freed from its origins o n the lateral pterygoid plate and the greater w ing of the sphenoid bone. T h e neck of the condyle is sectioned h o r iz o n ta lly . U s in g th e c o n d y le as a handle, tension is placed on the capsule of the T M J an d the capsule is detached from the skull by sharp dissection from th e la te ra l m uscle. N ex t, the d isk can be retrac te d laterally an d in fe rio rly so th a t the in n e r attachm ents of the capsule
can be reached to be severed w ith a scalpel. T h e disk can then be rem oved w ith the lateral pterygoid m uscle; the zygom atic bone section an d all o th er attach m en ts are intact at one end. Discussion
A lth o u g h th ese m u sc le s a re p ro b a b ly derived em bryologically from the m asseter m u sc le , th ey d iffe r in th e ir in s e rtio n a n d o r ig in . T h e m a n d ib u la r d isk a l m uscle o rig in ates in com m on w ith the in s e rtio n of th e deep m asseter m u scle a n d inserts on the lateral p o rtio n of the anterior b an d of the articu lar disk. T h e z y g o m atico d isk al m u scle o rig in a te s in com m on w ith the o rig in of the deepest m a sse te r m u sc le a n d in s e rts o n th e an terio r b an d of the articu la r disk ju st m edial to the m an d ib u lar diskal muscle. T h e in n e rv a tio n is o b v io u sly th ro u g h the m asseteric nerve th at passes between these two muscles an d the distal border o f th e te m p o ra lis m u sc le a n d te n d o n to the coronoid process. T h ese tw o m uscles vary in size an d shape in all dissections w ith the inserting te n d o n s u s u a lly c o n v e r g in g n e a r th e anterior b and of the disk. T h e m an d ib u lar diskal m uscle often has two, or in one case, three separate tendons converging o n th e a r tic u la r d isk . T h e o r ig in s o f th e m u sc le fib e rs in v o lv e d in th ese separate tendons likewise have diverging attachm ents, often in a fanlike arran g e ment. P art of the o rig in of this m uscle is often on the fascia of the in n erm o st
ARTICLES
deep m asseter m uscle. In the fetus d issected , how ever, the m u scles were isolated in to com p letely separate and distinct bundles with a com m on tendon of insertion to the articular disk. T h e m andibular diskal m uscle origin is to the lateral surface of the mandible, just at and b elo w the m an d ib u lar n otch without attachment to the fascia of the deep masseter m uscle. T h e zygom aticodiskal o rigin is circum spect w ith ou t the m ixing of fibers from the origin of the deep masseter muscle or the crossing fibers to the temporalis fascia. T he two m uscles make a distinct, inverted "L ” shape. More fetal dissections are planned to investigate the variation between the adult and fetus as the difference is definite in one case. The size variation in relation to gender needs to be investigated as this may be im p o rta n t in the ob viou s gender d if ference (reportedly seven female to three m ale) in the occurrence o f TM J dysfunction. Presence of these two muscles w ould h o ld the d isk an teriorly w ith active tension in three p osition s rather than an active force p ulling only in a medioanterior direction in the form of the superior head of the lateral p terygoid m uscle. T his muscle was thought to be resisted in the lateral direction only by the lateral collateral ligam ent. T h is interm ittent tension placed on the lateral collateral ligam ent w ould tend to stretch it and cause more dysfunction than is found. W hen d y sfu n ctio n is caused by an o v er w h e lm in g force o f any k ind , the zygom adcodiskal m uscle sim ply turns at right angles toward the medial as the mandibular diskal muscle falls through
the mandibular notch. In treating patients for some time, an unusual soreness has been n oted deep in the area o f the mandibular notch that was not explain able. This may be from the repositioning of these muscles into a position where they m ust again becom e active after a lo n g period of in activity. W hen these muscles are in place, there is an active tension caused by the mandibular diskal muscle in an inferoanterolateral direction that pulls down on the helmetlike disk, and tends to hold it in place. T his may be an exp lan ation o f the relative lack of relapse after successful disk replace ment. If the disk is held in place long enough, there may be repair of the lateral collateral ligament in spite of the sparse blood supply. Summary
T h e presence of these tw o m uscle at tachm ents w ill be h elp fu l in treating TM disorders. Why they have not been previously described is a mystery, but it is m ore u nd erstan dab le w hen the difficulty of dissection is noted. Freeing the disk w hile investigatin g the retrodiskal area, and then performing fiberby-fiber dissection of the deep masseter muscle are uncomm on procedures. Mus cle fibers often e x ist from the deep m asseter m uscle to the cap su le o f the TM J, and these m u scles co u ld easily be mistaken for the fibers already known and, therefore, ignored when the masseter was removed in dissection. If the first specimen dissected had not been a welld evelop ed m ale w ith stro n g tendon attachment, the attachments w ould have been missed in this case as well.
-------------------- J!*OA -------------------T h e author thanks W illiam Knisely, PhD , dean of graduate studies; K. K. Faulkner, PhD , chairman of the department of anatomy; W. J. L. Felts, PhD, department of anatomy; D. Feeback, PhD , department of anatomy; and Pam Lawson of the basic science d iv is io n , U n iv e r sity o f O k la h o m a C o lle g e s o f M ed ic in e an d D en tistry, for h e lp in d is s e c tio n , availability of laboratory space, and obtaining the large num ber o f specim ens used in th is series of dissections. A lth o u g h a library search w as m ade for any reference to these muscles and none found, the search w as carried further by c o n ta c tin g oth er p erson s in terested in b asic research in T M J. Dr. Parker M ahan, by te le p h o n e, m e n tio n e d th at a m u scle was described by R ichard Koritzer, D D S, Ph D , of G len Burnie, MD, that was sim ilar to the mandibular diskal muscle. It is not know n at this time if this is the same muscle described here or is an anterior, m ore su p erficia l e x te n sio n o f the d eep m asseter m u scle as he nam es it the m an d ib u lar capsular. It should be noted, however, that the m uscle may have been reported previously. Several references pertaining to this research are included. Dr. Myers is in private practice w ith an interest in temporomandibular dysfunction, and is researcher, departm ent of anatom y, U niversity o f Oklahom a. Address requests for reprints to the author at 509 W Gore Blvd, Lawton, OK 73501. 1. Scott, J.H . T h e grow th and fu n ctio n o f the muscles of m astication in relation to the developm ent o f the facial skeleton and of the dentition. Am J Orthod 40:429-499, 1954. 2. Sym ons, N .B. T h e attachm ent of the muscles o f mastication. Br Dent J 96:76-81, 1954. 3. R ees, L .A . Stru cture an d fu n c tio n o f the mandibular joint. Br Dent J 96:125-133, 1954. 4. Carlson, D.S. Growth of the masseter m uscle in Rhesus monkeys (Macaca Mulatta). Am J Phys A nthropol 60:401-410, 1983. 5. Procter, A .D ., and D eV incenzo, J.P. Masseter m uscle position relative to dentofacial form. A ngle Orthod 40:37-44, 1970. 6. Herring, S.W., and W ineski, L.E. D evelopm ent o f the m asseter m u scle and oral behavior in the pig. J Exp Zool 237:191-207,1986.
Myers : NEW MUSCLE ATTACHMENTS TO TMJ DISK ■ 439
This article describes the accidental discovery of additional muscle attachments to the temporomandibular join t articular disk. Previously, only one muscle attachment has been reported in the literature. This discovery may provide valuable information for the clinician treating temporomandibular disorders.
Newly described muscle attachments to the anterior band of the articular disk of the temporomandibular joint L. J. Myers, DDS
n til this tim e, only one m uscle h as been k n o w n to a tta c h to the a rtic u la r disk of th e te m p o ro m an d ib u lar jo in t (TM J). T h is was the superior head of the lateral pterygoid m uscle that acted to m aintain the position of the disk on the condyle w hile closing. T h e o n ly la te r a l a tta c h m e n t w as th e lateral collateral ligam ent th a t attached the disk to the lateral pole of the condyle of the m andible. T h is lack of ligam ent a n d m u scle a tta c h m e n t has seem in g ly c o m p ro m ise d th e “ p e r m a n e n t” r e p a ir of the disk-condyle system after displace m e n t of th e d isk a n d th e c o n s e q u e n t s tr e tc h in g o r te a r in g o f th e la te r a l c o lla te r a l lig a m e n t a n d s tr e tc h in g of th e p o ste rio r elastic la m in a a tta c h in g th e d isk to th e p e tro ty m p a n ic fissu re of the skull. A lth o u g h successful re p o sitio n in g of the disk o n the condyle is now com m on place, this has been th o u g h t of as m ore of a “ tem porary” success as the dam age already done in the displacem ent makes the disk highly unstable. T heoretically, rep air an d reposition w ould need to be re p e a te d . R e la p se of p ro p e rly tre a te d disk displacem ents has, however, proved to be the exception rather th an the rule. T h e puzzle is pieced by the understanding of new muscles described in this article. T h e presence of previously u n rep o rted muscles w ould explain why repositioning
U
the disk on the condyle is m ore successful th a n w ould be expected. Methods and materials
T h e se m uscles w ere fo u n d by accident d u rin g a tedious p ro ced u re th a t is not
o ften p erfo rm e d o n th e d eep m asseter m uscle. A previous dissection h ad been perform ed, freeing the disk to study the retrodiskal tissues by sectioning the skull vertically th ro u g h the external auditory canal. T h e m asseter m uscle fibers were b e in g dissected a n d c h a rte d fo r vector
F ig 1 ■ N ew ly described m u scle attachm ents to the anterior band o f the articular disk o f the tem p orom andib ular jo in t in m ale specim ens. Key: 1 = head of con d yle, 2 = zygom a, 3 = deep m asseter m u scle, 4 = zygo m a tico d isk a l m u scle (n ew ), 5 = m an d ib u lar d isk a l m u sc le (n ew ), 6 = anterior band of articular disk, and 7 = superior head of lateral pterygoid muscle.
JADA, Vol. 117, September 1988 ■ 437
A R T I C L E S
analysis. After reaching the deepest fibers of this m uscle an d detaching them from the zygom atic process (and in this case th e la te r a l su rfa c e of th e a r tic u la r ca p su le ),1 6 it was seen th a t there were d e e p e r fib e rs th a t w ere a tta c h e d in com m on w ith deep m asseter m uscle fibers ju st below the m a n d ib u la r notch on the la te r a l su rfa c e of th e m a n d ib le . T h e d irectio n of the fibers was n o t p arallel to the deep masseter fibers, b u t deviated posteriorly 30°. W h e n te n s io n w as a p p lie d to these fib e rs, th e a r ti c u la r d isk , w h ic h w as prev io u sly loosened, was seen to m ove fo rw ard . T o m o re closely observe the attachm ent, the zygom atic arch was cut w ith a reciprocal saw at its anterior end an d ag a in in a m edio an terio r direction above th e condyle to av o id d is ru p tin g th e a n te r io r b a n d of th e disk w ith its attachm ents. After everting the zygomatic arch , a second set of fibers w as found in th e in n e r su rfa ce o f th e zygo m atic arch, a n d in se rtin g on the m iddle p art of th e a n te r io r b a n d of the disk. T h e fib ers o r ig in a tin g o n th e m a n d ib u la r no tch inserted laterally to this but were still o n the anterior p o rtio n of the anterior band. At th a t tim e, kn o w in g there were no reported muscles w ith these origins and in se rtio n s, the h ead of the d ep a rtm en t of anatom y was called to see the discovery. H e dissected the m a n d ib u la r head free of its fibers to its insertion a n d origin, an d suggested that p h o to g rap h s be taken an d o th e r heads exam ined in the same way to determ ine if this was an anom aly. C u rre n tly , d iss e c tio n s h av e b een p e r form ed on 14 other adults, one full-term fetus, a n d one M acaca m onkey. In all specim ens, these muscles have been found alth o u g h they have varied in size in the d ifferen t specim ens. T h e re seems to be a gender difference w ith the female not as w ell d e v e lo p e d , b u t w ith so few specim ens it cannot be deem ed universal. T h e fetus was m ale a n d the tw o muscles were w ell differentiated. In the monkey, th e m uscles w ere p rese n t ag a in . In all cases, the m an d ib u la r diskal muscle was s e p a ra te fro m th e p o s te rio r b o rd e r of the tem poralis m uscle w ith the masseteric nerve p a s sin g betw een th e tw o m asses of m u sc le fib ers. In o ld e r sp e cim en s, the zygom aticodiskal m uscle showed an increase in fibrous tissue w ith consequent loss of m uscle fibers. T h is same finding was n o t seen in the m a n d ib u la r diskal m uscle (Fig 1, 2). In later dissections it was found that the best way to show these muscles was 438 ■ JADA, Vol. 117, September 1988
Fig 2 ■ Photographs, top left and right, and bottom left, show new ly described m uscle attachments in female specim ens. Bottom right show s same in male fetus (Key: same as in Fig 1).
to remove the jo in t ap p aratu s com pletely as follows. W ith the b rain rem oved and the head sectioned sagittally, the vertical cut is m ade w ith a reciprocal saw through the external auditory canal. T h is leaves o n ly a sm a ll se c tio n o f th e ty m p a n ic plate b ehind the T M J. In m ost specim ens, th is is easily rem oved a t the p etro ty m p a n ic fissure. T h is exposes the cran ial a tta c h m e n t of the su p e rio r retro d isk a l lam ina. T h e superficial lam in ae of the m a sseter m u scle are rem o v ed , le a v in g on ly the deep lam in ae. T h e zygom atic a rc h is th e n c u t v e rtic a lly in fro n t of the zygom aticotem poral suture and again at a 45° ang le postero an terio rly ju s t in front of the lateral pole of the condyle, le a v in g th e o r ig in o f th e r e m a in in g m a sse te r in ta c t. T h is o p e n s u p th e coro n o id process th a t is then cu t h o ri zontally for the rem oval of the tem poralis m uscle. T h e tem poralis m uscle is then rem oved by d issection a t th e o rig in at th e side of th e sk u ll. W ith b lu n t d is section, the tem poralis m uscle is removed w ith th e c u t p o r tio n of th e c o ro n o id pro ce ss. T h is o p e n s u p th e la te ra l pterygoid muscle, w hich is carefully freed from its origins o n the lateral pterygoid plate and the greater w ing of the sphenoid bone. T h e neck of the condyle is sectioned h o r iz o n ta lly . U s in g th e c o n d y le as a handle, tension is placed on the capsule of the T M J an d the capsule is detached from the skull by sharp dissection from th e la te ra l m uscle. N ex t, the d isk can be retrac te d laterally an d in fe rio rly so th a t the in n e r attachm ents of the capsule
can be reached to be severed w ith a scalpel. T h e disk can then be rem oved w ith the lateral pterygoid m uscle; the zygom atic bone section an d all o th er attach m en ts are intact at one end. Discussion
A lth o u g h th ese m u sc le s a re p ro b a b ly derived em bryologically from the m asseter m u sc le , th ey d iffe r in th e ir in s e rtio n a n d o r ig in . T h e m a n d ib u la r d isk a l m uscle o rig in ates in com m on w ith the in s e rtio n of th e deep m asseter m u scle a n d inserts on the lateral p o rtio n of the anterior b an d of the articu lar disk. T h e z y g o m atico d isk al m u scle o rig in a te s in com m on w ith the o rig in of the deepest m a sse te r m u sc le a n d in s e rts o n th e an terio r b an d of the articu la r disk ju st m edial to the m an d ib u lar diskal muscle. T h e in n e rv a tio n is o b v io u sly th ro u g h the m asseteric nerve th at passes between these two muscles an d the distal border o f th e te m p o ra lis m u sc le a n d te n d o n to the coronoid process. T h ese tw o m uscles vary in size an d shape in all dissections w ith the inserting te n d o n s u s u a lly c o n v e r g in g n e a r th e anterior b and of the disk. T h e m an d ib u lar diskal m uscle often has two, or in one case, three separate tendons converging o n th e a r tic u la r d isk . T h e o r ig in s o f th e m u sc le fib e rs in v o lv e d in th ese separate tendons likewise have diverging attachm ents, often in a fanlike arran g e ment. P art of the o rig in of this m uscle is often on the fascia of the in n erm o st
ARTICLES
deep m asseter m uscle. In the fetus d issected , how ever, the m u scles were isolated in to com p letely separate and distinct bundles with a com m on tendon of insertion to the articular disk. T h e m andibular diskal m uscle origin is to the lateral surface of the mandible, just at and b elo w the m an d ib u lar n otch without attachment to the fascia of the deep masseter m uscle. T h e zygom aticodiskal o rigin is circum spect w ith ou t the m ixing of fibers from the origin of the deep masseter muscle or the crossing fibers to the temporalis fascia. T he two m uscles make a distinct, inverted "L ” shape. More fetal dissections are planned to investigate the variation between the adult and fetus as the difference is definite in one case. The size variation in relation to gender needs to be investigated as this may be im p o rta n t in the ob viou s gender d if ference (reportedly seven female to three m ale) in the occurrence o f TM J dysfunction. Presence of these two muscles w ould h o ld the d isk an teriorly w ith active tension in three p osition s rather than an active force p ulling only in a medioanterior direction in the form of the superior head of the lateral p terygoid m uscle. T his muscle was thought to be resisted in the lateral direction only by the lateral collateral ligam ent. T h is interm ittent tension placed on the lateral collateral ligam ent w ould tend to stretch it and cause more dysfunction than is found. W hen d y sfu n ctio n is caused by an o v er w h e lm in g force o f any k ind , the zygom adcodiskal m uscle sim ply turns at right angles toward the medial as the mandibular diskal muscle falls through
the mandibular notch. In treating patients for some time, an unusual soreness has been n oted deep in the area o f the mandibular notch that was not explain able. This may be from the repositioning of these muscles into a position where they m ust again becom e active after a lo n g period of in activity. W hen these muscles are in place, there is an active tension caused by the mandibular diskal muscle in an inferoanterolateral direction that pulls down on the helmetlike disk, and tends to hold it in place. T his may be an exp lan ation o f the relative lack of relapse after successful disk replace ment. If the disk is held in place long enough, there may be repair of the lateral collateral ligament in spite of the sparse blood supply. Summary
T h e presence of these tw o m uscle at tachm ents w ill be h elp fu l in treating TM disorders. Why they have not been previously described is a mystery, but it is m ore u nd erstan dab le w hen the difficulty of dissection is noted. Freeing the disk w hile investigatin g the retrodiskal area, and then performing fiberby-fiber dissection of the deep masseter muscle are uncomm on procedures. Mus cle fibers often e x ist from the deep m asseter m uscle to the cap su le o f the TM J, and these m u scles co u ld easily be mistaken for the fibers already known and, therefore, ignored when the masseter was removed in dissection. If the first specimen dissected had not been a welld evelop ed m ale w ith stro n g tendon attachment, the attachments w ould have been missed in this case as well.
-------------------- J!*OA -------------------T h e author thanks W illiam Knisely, PhD , dean of graduate studies; K. K. Faulkner, PhD , chairman of the department of anatomy; W. J. L. Felts, PhD, department of anatomy; D. Feeback, PhD , department of anatomy; and Pam Lawson of the basic science d iv is io n , U n iv e r sity o f O k la h o m a C o lle g e s o f M ed ic in e an d D en tistry, for h e lp in d is s e c tio n , availability of laboratory space, and obtaining the large num ber o f specim ens used in th is series of dissections. A lth o u g h a library search w as m ade for any reference to these muscles and none found, the search w as carried further by c o n ta c tin g oth er p erson s in terested in b asic research in T M J. Dr. Parker M ahan, by te le p h o n e, m e n tio n e d th at a m u scle was described by R ichard Koritzer, D D S, Ph D , of G len Burnie, MD, that was sim ilar to the mandibular diskal muscle. It is not know n at this time if this is the same muscle described here or is an anterior, m ore su p erficia l e x te n sio n o f the d eep m asseter m u scle as he nam es it the m an d ib u lar capsular. It should be noted, however, that the m uscle may have been reported previously. Several references pertaining to this research are included. Dr. Myers is in private practice w ith an interest in temporomandibular dysfunction, and is researcher, departm ent of anatom y, U niversity o f Oklahom a. Address requests for reprints to the author at 509 W Gore Blvd, Lawton, OK 73501. 1. Scott, J.H . T h e grow th and fu n ctio n o f the muscles of m astication in relation to the developm ent o f the facial skeleton and of the dentition. Am J Orthod 40:429-499, 1954. 2. Sym ons, N .B. T h e attachm ent of the muscles o f mastication. Br Dent J 96:76-81, 1954. 3. R ees, L .A . Stru cture an d fu n c tio n o f the mandibular joint. Br Dent J 96:125-133, 1954. 4. Carlson, D.S. Growth of the masseter m uscle in Rhesus monkeys (Macaca Mulatta). Am J Phys A nthropol 60:401-410, 1983. 5. Procter, A .D ., and D eV incenzo, J.P. Masseter m uscle position relative to dentofacial form. A ngle Orthod 40:37-44, 1970. 6. Herring, S.W., and W ineski, L.E. D evelopm ent o f the m asseter m u scle and oral behavior in the pig. J Exp Zool 237:191-207,1986.
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