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Standards

Temporomandibular Joint (TMJ)

DAVID DEAN
Department of Anatomy
Case Western Reserve University Medical School
10900 Euclid Avenue
Cleveland, OH 44106-4930

June 2, 1994

Its behavior makes the TMJ one of the most complex joints in the human body. The primary and stylized behavior to which the joint is adapted is chewing hard. During forceful mastication the postcanine dentition on only one side of the side of mandible (the "working side") undergoes repetitive mediolateral circular motions (the "power stroke"). The contralateral side (the "balancing side") muscles generate the necessary force. The balancing and working side alternate, unconsciously, in the vast majority of individuals. During mastication the balancing side TMJ serves as the fulcrum; more specifically, the condylar head moves anteriorly (slides) and presses against the articular eminence of the articular disc (Hylander, 1979; Walker, 1978;Dean, 1986). Proof of this model comes from individuals with unilateral damage of the TMJ; they report pain when chewing occurs on the opposite side.

Kinematic models of mastication concentrate on the position the balancing side condyle takes versus the articular tubercle during forceful occlusion. The entire mandible undergoes the circular power stroke in this position, however during each chewing cycle the balancing side condylar head moves anteroinferiorly then medially before returning to its original position (Dubrul, 1980). The oblique and horizontal fibers of the "TMJ ligament," found lateral to the joint capsule, help prevent posterior and anterior overexcursion, respectively (Aiello and Dean, 1990). Most commonly, the mandibular foramen has been chosen as the center of rotation during the anterior excursion that occurs during chewing (Rees, 1954; Smith, 1985).

Geometrically, the axis of mastication at the mandibular foramen (point 4) could be best modeled as the perpendicular intersecting a plane created from three dimensional coordinates at points 1, 3, and 5 in figure 1. The other points offered may be useful for specimens or patients viewed either radiologically or in surgeries requiring tactile location. Most of these landmarks are curvature extrema the others are intersections of various tissues and/or bone.

Figure 1: Lateral view of a hemimandible (modified from Aiello and Dean,1990). Locations of landmarks: point 1: coronoid tip; point 2: bottom of the mandibular notch; point 3: internal-most condylar head; point 4: mandibular foramen as represented by tip of lingula; point 5: angle of mandible (gonion); point 6: inferoanterior-most point (menton); point 7: anterior most point on corpus (pogonion); point 8: midpoint on alveolar margin between lower central incisors.
Figure 2: Lateral view of temporomandibular joint (modified from Aiello andDean, 1990). Locations of landmarks: point 9: external-most condylar head(condylion); point 10: inferior-most mastoid process (mastoidale); point11: inferior-most external auditory meatus; point 12: superior-most external auditory meatus (porion); point 13: superolateral-most point glenoid fossa; point 14: inferolateral-most point articular eminence (articulare); point 15: superolateral-most point on arc between articulare and anterior masseteric tubercle; point 16:anteroinferior-most point along superior edge of zygoma.

References

Aiello L and Dean MC (1990) Human Evolutionary Anatomy. London: AcademicPress.

Dean D (1986) Covariation between craniofacial form and chewing. M.A. thesis: Temple Univ. Ann Arbor: University Microfilms.

Dubrul EL (1980) Sicher's Oral Anatomy. St. Louis: Mosby.

Hylander, WL (1979) An experimental analysis of temporomandibular joint reaction force in macaques. Am. J. Phys. Anthropol. 51:433-456.

Walker AC (1978) Functional anatomy of oral tissues: Mastication and deglutination. In (JH Shaw, EA Sweeney, CC Cappuccino, and SM Meller, eds.): Textbook of Oral Biology.