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Jaw Clenching: Muscle and Joint Forces, Optimization Strategies

¹ Research Group Biomechanics, Faculty for Mathematics, University of Karlsruhe, D-76128 Karlsruhe, Germany;
² Department of Reconstructive Dentistry and Temporomandibular Disorders, Dental School, University of Basel, Switzerland;
³ Department of Prosthodontics, University of Heidelberg, Germany; and
⁴ Department of Prosthodontics, Dental School, University Hospital Freiburg, Germany

^* corresponding author, myo.schindler{at}t-online.de

Realistic masticatory muscle and temporomandibular joint forces generated during bilateral jaw clenching are largely unknown. To determine which clenching directions load masticatory muscles and temporomandibular joints most heavily, we investigated muscle and joint forces based on feedback-controlled electromyograms of all jaw muscles, lines of action, geometrical data from the skull, and physiological cross-sectional areas acquired from the same individuals. To identify possible motor control strategies, we applied objective functions. The medial pterygoid turned out to be the most heavily loaded muscle for all bite directions. Biting with accentuated horizontal force components provoked the highest loading within the medial and lateral pterygoids. The largest joint forces were also found for these bite directions. Conversely, the lowest joint forces were detected during vertical biting. Additionally, joint forces with a clear posterior orientation were found. Optimization strategies with the elastic energy as objective function revealed the best fit with the calculated results.

KEY WORDS: jaw muscles • joint forces • muscle forces • EMG • optimization