Characterisation of human jaw biomechanics based on screw theory

Abstract

In this paper the characterisation of jaw-mechanics, by means of the motion screw and the wrench, is presented demonstrating its ability to provide a simplified, yet complete description of jaw function. Motion data and anatomical data from a single subject is used to implement the screw theory approach where the muscle forces are represented at each instant during the movement by a unique screw or wrench while the jaw-movement characteristics are described by another screw, the motion screw, resulting in a simplified representation of the 3D-mechanics of the jaw. The combined wrench and motion screw representation is used to construct an integrated computer model of jaw biomechanics. The results of an experimental program, involving Magnetic Resonance (MR) imaging for obtaining accurate anatomical representations of the masticatory muscles and the bony structures, as well as jaw-motion data collected via an optoelectronic recording instrument, are presented. The results show that the experimentally derived, screw-based model conforms to the clinically observed behaviour of jaw function and can provide a quantitatively accurate means of analyzing mandibular biomechanics.

Keywords:

• Mandibular mechanics
• wrench axis
• motion screw

Additional information

Notes on contributors

J A Gal

Graduating from the University of Sydney with a BSc and BEng (Hons), Dr John Gal gained an MEngSc in jaw-kinematics and completed his PhD, in 1984, in the robotics area. He joined Sydney University as Lecturer in 1994 and since 1996 he is Senior Lecturer in Robotic & Mechatronic Engineering at the University of Western Sydney. His main areas of research involve jaw-mechanics, collaborating with the Universities of Zurich and Sydney, winning an ARC Large Grant for this work (1997). He has published in the last five years 15 journal and conference papers in biomedical applications, robotics and industry automation.

L M Gallo

Dr Luigi M. Gallo graduated in Electrical Engineering from the Swiss Federal Institute of Technology (ETH), Zurich. After his doctorate he has become Director of the Experimental Laboratory at the Clinic for Masticatory Disorders and Complete Dentures at the Dental School in Zurich. He is a “Privatdozent” in Biomedical Engineering at the Faculty of Medicine with research interests involving the development and use of innovative hardware and software for the non-invasive study of function and dysfunction of the masticatory system. In the last few years he has published over 25 papers in peer reviewed journals on biomedical and dental research.

S Palla

Professor Iven Klineberg AM, RFD is Professor of Prosthodontics and Head - Jaw Function and Oro-facial Pain Research Unit at the University of Sydney. He graduated from that institution BDS(1963), MDS(1966) and BSc (1968) . He obtained his PhD from University of London (1971) becoming Commonwealth Medical Fellow, Royal College of Surgeons of England and FDSRCS(Eng). He has been Visiting Professor at the University of Michigan (1977-8) and Dean, Faculty of Dentistry at University of Sydney (1991-8). Areas of clinical interest include TMD and oral implant restoration while research includes occlusion relating to TMjoint neurology, jaw muscle function and dysfunction.

G M Murray

Greg Murray is an Associate Professor in the Faculty of Dentistry, University of Sydney. He graduated BDS (Hons) from the University of Sydney in 1980, obtained his FRACDS in 1983, MDS in 1984, and PhD in 1990. His PhD supervisor was Professor Barry Sessle (Toronto, Canada) and the work focussed on the cerebral cortical control of orofacial movements. He has been at Sydney University since 1990 and has published 50 papers, 7 book chapters and 100 conference abstracts. He is a member of a number of societies including the Society for Neuroscience and the International Association for Dental Research.

I J Klineberg

Professor Sandro Palla is Chairman of the Department of Masticatory Disorders and Complete Dentures at the Dental School of the University of Zurich since 1981. His research interests include MR imaging, mandibular kinesiology and the development of non-invasive techniques to study the loading conditions of the temporomandibular joint.

C W Johnson

Chris Johnson is a Senior Lecturer in Computer Systems, Faculty of Information Technology, at the University of Technology, Sydney. He has been involved in the study of muscle activation in mandibular function with the University of Sydney where he has been undertaking a PhD program in this area. His research interests include EMG recordings of muscle activity as well as computer modeling and simulation of jaw function.