Multibody dynamics modelling of the masticatory system of the house mouse (Mus musculus)

Chabokdast, Anna

May 2015

Thesis or dissertation

© 2015 Anna Chabokdast. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

Understanding the function of masticatory system of the mouse, the model of choice for craniofacial studies is invaluable, yet has been investigated poorly. Multibody dynamic analysis (MDA), which is a 3D computer modelling technique used in this study, is ideally suited to replicate and investigate this complex system. To mechanically solve this intricate system, system indeterminacy should be tackled using optimisation algorithms. The mouse has two types of teeth, hence two very different types of biting: incisal and the molar biting. To understand the masticatory function, modelling these two types of biting is invaluable. This study aims to investigate the differences in muscle function between incisors and molar biting. It was hypothesized that the generated bite force in the first molar would be higher than the incisor, due to the mechanical advantage of the latter. Moreover, the model sensitivity to the optimisation algorithms and the constraint types as well as muscle attributes such as intrinsic stress value and cross sectional area were studied. Functional development of the masticatory system of the mouse was an additional interest in this study.

The first MDA model of the adult mouse masticatory system was developed and two optimisation algorithms, Dynamic geometric optimisation (DGO) and minimisation of overall muscle energy (MOME), were used to overcome the system indeterminacy. Furthermore, individual-specific adult model were developed and maximal and sub-maximal incisor and first molar biting were simulated. In addition, a simplistic model of the juvenile incisal biting was developed in which maximal incisal bite force and muscle activation pattern was studied.

Some divergences were predicted from DGO and MOME, which were resulted from different basis of the activation factors in the two algorithms. Nevertheless, DGO was chosen as the optimisation algorithm mainly because it allowed for the simulation of a full biting cycle and for inclusion of some key developments in the future. The maximum predicted bite force in incisal biting was lower than the in vivo measurement, which was possibly due to averaging PCSA across specimens. A correction factor of 25% was added to muscle intrinsic stress value to compensate for this underestimation. Moreover as expected, the maximum predicted bite force at the first molar position was larger than that of the incisor. It was also found that the ratio of muscle forces between incisal and molar biting did not remain constant, however, was more consistent for simulation of low bite forces. In addition, incisal bite force in juvenile model was in agreement with in vivo bite force measurement from the same individual.

MDA presented here provides a model which may be used to study many functional tasks and to investigate functional development and intertwined relationship between function and development in the mouse and similar rodents.

Hull York Medical School, The University of Hull and the University of York
Cobb, Samuel N.; Fagan, M. J. (Michael J.), 1957-
Sponsor (Organisation)
University of Hull
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