A model for mylohyoid muscle mechanics

The purpose of the present study was to develop a mathematical model of the mylohyoid muscle allowing to analyze the complex mechanics of the muscle d uring jaw movement. The model was based on muscle morphology and physiologi cal properties. Bending: of fibers was incorporated into the model by pulle ys located along the upper lateral border of the anterior belly of the diga stric muscle. The dynamical properties of the muscle portions, i.e. force-l ength and force-velocity relationships, were related to sarcomere length ch anges. In addition, the effective force component produced by each portion in the sagittal plane was calculated. The model provided information on the geometrical changes of the muscle portions and the concomitant effect on s arcomere length, dynamical properties and effective force component as a fu nction of jaw opening angle. Muscle configuration changed drastically and n on-uniformly during jaw opening. However, sarcomere length changes were rel atively small and differed but slightly between the muscle portions. The mu scle portions all operated near optimum length regarding to their force-len gth relationship. In all muscle portions effective muscle force was the sma llest (10-20% of maximum isometric force) in the beginning of the opening m ovement. With an increase of jaw angle effective muscle force gradually inc reased to 60-70% of maximum isometric force in the posteriormost muscle por tion and to 20% in the anterior-most portion. Muscle fiber bending appeared to increase the sagittal plane component of the muscle force substantially . (C) 1998 Elsevier Science Ltd. All rights reserved.