A three-dimensional mathematical model of temporomandibular joint loading

Objective. A mathematical model of the temporomandibular joint was develope d to study the magnitude and direction of the compressive loading experienc ed at the temporomandibular joint during clenching. Design. The model was based on the principles of static equilibrium in thre e dimensions. Background Direct measurement of temporomandibular joint loading in humans is extremely difficult. Animal models have provided an alternative in the p ast. However, evidence suggests that primates are not the most accurate hum an analogues for temporomandibular joint studies. A mathematical model was used as an alternative to direct measurement. Methods. The EMG activity of two masticatory muscles was combined with thei r cross-sectional areas to calculate the force exerted by each muscle. Expe rimentally determined forces were implemented into a quadratic programming model to solve for the compressive forces on the joint. Two objective funct ions were chosen and their ability to predict muscle and joint forces was e valuated. Results. The maximum bite forces for normal men, normal women. and women wi th temporomandibular joint disorders were 300 N (SD 102 N), 210 N (SD 57.7 N), and 120 N (SD 77.1 N). respectively, The calculated joint force for nor mal males was 260 N (SD 84.1 N). Normal females and female temporomandibula r joint disorder patients produced temporomandibular joint forces of 172 N (SD 37.5 N) and 152 N (SD 44.2 N), respectively.