3035 Dynamic simulation of different occlusal schemes during tooth clenching
K. YASHIRO, C.C. PECK, and A.G. HANNAM, University of British Columbia, Vancouver, Canada

The differential stiffness of the teeth and temporomandibular joints (TMJs) permits jaw motion during tooth clenching, and suggests dynamic modeling may be an appropriate way to study muscle, tooth and joint forces. Objectives: To compare tooth and joint reaction forces for 4 different occlusal schemes (Class I, II, anterior and posterior open-bites) during simulated tooth clenching. Methods: 3D mathematical models of the human jaw were developed with dynamics software (ADAMS 10.0; MD Inc, MI). The models' structural and functional components were based on a previous human jaw model (Langenbach and Hannnam, 1999). Regionally specific viscoelastic properties were used at condylar and posterior dental contact sites (condylar:60N/mm; molar:160N/mm; premolar:110N/mm). The TMJ was modeled with a "sphere within sphere" contact algorithm and occlusal contacts with multiple "sphere against sphere" contacts to simulate cuspal interactions. Dynamic clenching was simulated by uniform increases in temporalis, masseter and medial pterygoid activity to reach maximum muscle tensions in 0.5s. Results: Class I and Class II occlusions attained stable intercuspation. There was a progressive distribution of dental forces posteriorly with increasing elevator muscle activity. Joint loads increased rapidly to reach 150-170N during the initial 50% of muscle tension. A smaller incremental change of 20-30N was produced with further muscle activity. In contrast, the anterior and posterior open-bite models were unstable. They produced greater articular loads which increased progressively throughout clenching to reach maxima of 400 to 800N. Conclusions: Viscoelasticity appears to create complex interactions among articular and dental reaction forces. In the intact dental arch these dynamic changes appear to distribute occlusal forces more posteriorly with increasing bite force and reduce TMJ loads at high clenching levels. The high TMJ forces in open-bite occlusions predicted here are unlikely to occur in vivo where decreased and/or differential muscle contraction might be expected.

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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