3034 Dynamic changes in articular and occlusal forces during simulated tooth clenching
C.C. PECK, K. YASHIRO, and A.G. HANNAM, University of British Columbia, Vancouver, Canada

The differential stiffness of the teeth and temporomandibular joints (TMJs) suggests there may be sequential changes in their reaction forces during increasing muscle activity. Dynamic modeling is a useful way to study these interactions during tooth clenching. Objective: To predict dynamic changes in occlusal and TMJ loads during progressively increasing muscle contraction in the intercuspal position. Methods: A dynamic 3D human jaw mathematical model was constructed, which was based on one developed previously (Langenbach and Hannam, 1999) with dynamics software (ADAMS 10.0; MD Inc, MI). Articular (A) and occlusal (O) viscoelastic properties were derived from previous studies (Muhlemann, 1960; Siebert, 1981; Beek, 2001). Three different stiffness conditions tested the model's sensitivity viz., low (A: 30N/mm, molar O: 120N/mm), medium (A: 60N/mm, molar O: 160N/mm) and high (A: 90N/mm, molar O: 245N/mm). The TMJ was modeled with a “sphere within sphere” contact algorithm and occlusal contacts with multiple “sphere against sphere” contacts. Dynamic clenching was simulated by uniform increases in temporalis, masseter and medial pterygoid activity to reach maximum muscle tensions in 0.5s. Results: Increasing muscle tension caused increased occlusal forces, which transferred anteroposteriorly. This resulted in initial torque around a transverse axis through the jaw's mass center. With further tooth loading, the torque reversed. Joint forces increased more rapidly in the medium (134N) and high (174N) stiffness states to reach near maxima at 60% muscle activation. The resultant torques increased to maxima of 0.001Nm(low stiffness), 0.0007Nm (medium), 0.00055Nm(high) as maximum occlusal contacts were established. In the low stiffness states, joint forces steadily increased at 276N/s throughout the clenching task to a maximum of 138N. Conclusions: The model performed consistently for the different stiffness states however it was more sensitive to changes in articular than dental stiffness. Jaw torque reversals with steadily increasing muscle activation result from differential compression between articular and occlusal sites as muscle tensions increase.

Seq #275 - TMJ - Structure and Function II
3:45 PM-5:00 PM, Friday, 8 March 2002 San Diego Convention Center Exhibit Hall C

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