A Comprehensive Finite Element Model of the Human Masticatory System

Abstract

Understanding the role and mutual influence of the different components of the masticatory system during biting tasks is crucial for the improvement of the occlusal configuration of antagonistic teeth concerning CAD/CAM produced tooth reconstructions. The aim of this thesis is the creation of a comprehensive model of the stomatognathic system, which permits the reproduction of mandibular movements during the chewing act, including the micromovements of the teeth. The numerical model is based on the finite element method (FEM), which makes use of an explicit scheme for time discretization. The different tissues are represented by both, linear and non-linear material models, while contact is defined between the articular surfaces of the temporomandibular joint. A detailed explanation of the construction of the model is given, which includes the creation of the geometry of each component, the assembly process, the meshing process, and, finally, the proper allocation of material laws. Studies regarding the mineral tissue of the system focus on the first and third principal stresses developed in the mandibular bone during bilateral and unilateral biting as well as incisive biting. An analysis of tooth mobility while biting a deformable bolus is carried out for both, molar and incisive teeth, employing two different hyperelastic material models that lead to realistic force-displacement results. Since in soft tissues compressive loads are handled through a different mechanism than tensile loads, first and third principal stresses are investigated. A study of the performance of the temporomandibular joint follows, which gives attention to the behavior of the different attachments, and to the distribution of loads between the teeth and the joints, when different bite conditions are introduced in the mandible. Stress distributions in the articular disc are studied under several conditions, as well. A study of the role of the muscles ensues, regarding both the production of force as well as their passive reaction to stretching. Since investigations in the literature show a large variety of parameters for the muscles, multiple configurations are investigated involving different characteristic curves for the active and passive behavior of the muscles. Additionally, the kinetic mastication process is reproduced with the help of experimental data concerning the kinematics of the jaw and the measured electrical activity of the muscles during different biting tasks. Finally, the evolution of the movements and the forces on the teeth while in contact with the bolus, is investigated. In particular, the chewing simulations provide insight into the short-range kinetic interactions between antagonistic teeth during mastication, thus representing data of essential importance for ensuring interference-free fixed dental reconstructions. Furthermore, the model allows to examine the effect of rigid spacers between the jaws on the stress patterns in the articular discs, thus delivering information on the mechanism of various occlusal support conditions in the context of prosthetic reconstructions and splint therapy.