Biomechanical Modeling of the Masticatory Region

Abstract

Biomechanical simulation is an essential tool for the understanding of the human masticatory system, because many parameters and functions cannot be studied in vivo due to the invasiveness of their examination methods. Previous simulation studies include investigations of the masticatory cycle, the joint forces during opening and closing of the jaw and distraction osteogenesis. In this thesis we present projects that aim to increase the understanding of the masticatory system as well as to increase the availability of computational jaw models. We present a new optimization approach for inverse simulations that incorporates constraint reaction forces into the inverse solver. This method was used to develop an inverse dynamic biomechanical simulation of sleep bruxism. We also developed a detailed model of the sub compartments of the lateral pterygoid muscle, which we used to derive a theory that explains previously published EMG patterns during a contralateral movement of the mandible. Lastly, we investigated possible ways to port the ArtiSynth jaw model to OpenSim, which would increase its availability tremendously. To show that our optimization approach works correctly and enables us to set a predefined level of reaction force, we computed multiple simple simulations using a test model as well as an upper extremity model. Using a movement goal as well as a bite force goal we are able to realistically simulate teeth grinding behavior. Our simulations predict that bilateral masseter muscle activation is mainly concerned with the creation of closing force, while unilateral temporalis muscle activation is used to create the movement, necessary for tooth grinding. Due to the simulation set up submental activation could not be simulated, even though it is reported in literature. The simulation results for our new lateral pterygoid model show good iii agreement with activation recordings gathered using electromyography. Furthermore we developed a way to port muscle properties from ArtiSynth to OpenSim and designed a new representation of the temporomandibular joints that only uses one joint. Preliminary tests of dynamic jaw simulations in OpenSim show promising results. Together the contributions reported in this thesis have extended the capability and availability of biomechanical jaw modeling.