Biomechanical Models and the Analysis of Form: A Study of the Mammalian Masticatory Apparatus

Abstract

SYNOPSIS. Biomechanical models of the mammalian masticatory system were traditionally based on a simple classification of feeding types and prediction of function from form. The functional significance of spatial relationships between teeth, muscles and jaw joint, the shape of the mandible and sizes of the jaw muscles were explained in terms of optimal transmission of muscle forces to a specific bite point. Direct, experimental study of jaw movements and muscle activities has revealed new data, highly relevant to the construction of realistic mechanical models and the explanation of aspects of the morphology of the chewing apparatus. The jaw muscles do not reach comparable percentages of their maximum force simultaneously. The relative involvement of each muscle depends on the bite point. During mastication they fire in complicated patterns of successive, partially overlapping contractions. The linear relationship between electromyogram and muscular tension may be employed to estimate muscular tension in vivo. Computed resultant forces gradually change in magnitude and direction during chewing cycles; there is a close correlation with the jaw movements. The necessity to perform the movements may be an extra constraint on jaw muscle morphology. If muscle force estimates are used in a threedimensional static analysis, bite forces and joint reaction forces are found, different from those resulting from one- (simple lever) or two-dimensional static analysis. The explanation of tooth and joint morphology is influenced by these modifications.