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Dynamic Musculoskeletal Biomechanics in the Human Jaw

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Dynamic Musculoskeletal Biomechanics in the Human Jaw DYNAMIC MUSCULOSKELETAL BIOMECHANICS IN THE HUMAN JAW by CHRISTOPHER CHARLES PECK BDS, The University of Sydney, 1988 MSc(Dent), The University of Sydney, 1995 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Oral Biology) We accept this thesis as confonning to the required standard 'THE UNIVERSITY OF BRITISH COLUMBIA NOVEMBER 1999 ® Christopher Charles Peck, 1999 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Q/-«J "fct'ftlo^ ( 0>oJ W^oJfL £cwu,o The University of British Columbia Vancouver, Canada Date 2°V .NW*—\ \^ DE-6 (2/88) ABSTRACT The high prevalence of functional disorders in the human jaw emphasises the need to understand better its dynamic behaviour. In the present studies, dynamic mathematical models based on typical physical properties of the human jaw and skeletal muscles have been developed. In the first three studies, a model of the entire jaw was created and utilised to predict jaw elasticity and viscosity, and to simulate muscle-driven symmetrical and asvmmetrical jaw movements. Specifically these models were constructed without "ligaments" (temporomandibular capsule or other accessory jaw ligaments) to determine whether or not plausible motion could be simulated in their absence. In the fourth study, a specific model of the temporomandibular ligament and outer wall of the TMJ capsule was created to investigate further these passive structures' perceived role in constraining jaw movement. Variations in their structure have been implicated in jaw hypermobility and joint disorders. In the fifth study, a specific model of the masseter muscle was developed and consisted of six contiguous muscle compartments in which muscle fibre orientations and lengths differed. The functional implications of this complex internal structure was investigated when the model was stretched in opening and lateral jaw movements. In the first three studies, the jaw models required low elasticity and heavy damping to match in vivo conditions, and consequently low levels of muscle activity (tone) were needed to maintain a clinical jaw rest position. In the absence of "ligamentous" constraints about the jaw, plausible symmetric, and asymmetric movements were possible. In study four, putative capsular regions about the TMJ were suggested to remain taut throughout an entire ipsilateral jaw movement, however for contralateral, opening and protrusive jaw movements, the capsule remained slack during the middle third of the movement. In study five, although theoretically capable of generating high passive tensions, the masseter muscle model generated low overall passive tension to stretch. Dynamic modelling suggests hypothetical relationships between the jaw's structural and functional variables. Jaw muscle coactivation generates varied movements, and together with passive tensions affords a degree of jaw stability. Muscle and "ligaments" probably cooperate to constrain jaw movement, although muscle appears predominant in the mid- range of jaw movements. The internal structure of the masseter muscle may allow maximum movement with minimum passive tension generation. ii TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS iii LIST OF FIGURES ix LIST OF TABLES xiii ACKNOWLEDGMENTS xiv 1 INTRODUCTION 1 1.1 Introduction to the thesis 1 1.2 Jaw Structure 2 1.2.1 The craniomandibular skeleton ; 3 1.2.2 Temporomandibular Joint : 4 1.2.3 Muscles 6 1.3 Jaw Function 7 1.3.1 Methodology for measuring j aw function 8 1.3.1.1 Measurement of j aw kinematics 8 1.3.1.2 Measurement of bite force and electromyography (EMG) 10 1.3.1.3 Animal Studies 11 1.3.1.4 Modelling 12 1.3.1.4.1 Static Jaw Modelling 13 1.3.1.4.2 Muscle modelling 14 1.3.1.4.3 Dynamic Jaw Modelling 15 1.3.2 Jaw Motion 17 1.3.3 Jaw Muscle Function 19 1.3.3.1 Muscle Tension Generation 20 1.3.3.1.1 Maximum Muscle Tension 20 1.3.3.1.2 Active Muscle Tension 22 1.3.3.1.2.1. Length-tension and velocity-tension relationships 22 1.3.3.1.3 Passive Muscle Tension 23 iii 1.3.3.2 Muscle Activity 25 1.3.4 Jaw Loading 28 1.3.4.1 Condylar loading 30 1.4 Summary 33 2 STATEMENT OF THE PROBLEM : 35 3 DYNAMIC SIMULATION OF MUSCLE AND ARTICULAR PROPERTIES DURING WIDE JAW OPENING 38 3.1 ABSTRACT 38 3.2 INTRODUCTION 39 3.3 METHODS 41 3.3.1 Detenriination of Forces Required to Attain Wide-Gape 41 3.3.2 Definition of the Jaw Model 42 3.3.2.1 Mandible and Dentition 44 3.3.2.2 Temporomandibular Joints 45 3.3.2.3 Muscles 47 3.3.2.4 Specification of Muscle Fibre/Tendon Ratios 47 3.3.2.5 Specification of Muscle Tension Properties 49 3.3.2.5.1 Passive Muscle Tensions: 49 3.3.2.5.2 Active Muscle Tensions: 51 3.3.3 Jaw Dynamics 52 3.3.3.1 Determination of the Mandibular Rest Position (Model 40RP) 52 3.3.3.2 Muscle-Activated MiclJine Jaw Opening (Models' 40LF & 40XF) 52 3.3.3.2.1 Use of Linear Force-time Functions for Active Muscle Tensions (Model 40LF) 52 3.3.3.2.2 Use of Expanded Linear Force-time Functions for Active Muscle Tensions (Model 40XF) 54 3.3.3.3 Opening with Reduced Condylar Guidance (Models' 25PF, 25LF & 25XF) 54 3.3.3.4 Asymmetrical Opening (MODEL 40LF-As) 55 3.4 Results 55 3.4.1 Forces Required to Attain Wide-Gape 55 iv 3.4.2 Definition of the Jaw Model 3.4.2.1 Specification of Passive Muscle Tension Properties 3.4.3 Jaw Dynamics 3.4.3.1 Determination of the Mandibular Rest Position 3.4.3.2 Muscle-Activated Midline Jaw Opening 3.4.3.2.1 Use of Linear Force-time Functions for Active Muscle Tensions (Model 40LF) 3.4.3.2.2 Use of Expanded Linear Force-time Functions for Active Muscle Tensions (Model 40XF) 3.4.3.3 Opening with Reduced Condylar Guidance 3.4.3.4 Asymmetrical Opening 3.5 Discussion 3.5.1 Modelling Assumptions 3.5.2 Muscle Tensions 3.5.3 Mandibular Rest Position 3.5.4 Jaw Opening 3.5.5 Articular Loading 3.6 Conclusions 4 FORCES RESISTING JAW DISPLACEMENT IN RELAXED HUMANS: A VISCOELASTIC PHENOMENON 4.1 Abstract 4.2 Introduction 4.3 Methods 4.3.1 Mandibular Force-Motion Recordings 4.3.2 Mathematical Modelling 4.4 Results 4.4.1 Jaw Forces and Motions in Experimental Subjects 4.4.2 Mathematical Modelling 4.4.2.1 Critical Damping of the Mandible 4.4.2.2 Jaw Opening with Applied Force 4.5 Discussion 4.6 Conclusions 109 5 THE INFLUENCE OF MUSCLE CONSTRAINTS ON JAW MOVEMENTS 110 5.1 Abstract 110 5.2 Introduction Ill 5.3 Methods 114 5.3.1 Initial Jaw Positions 116 5.3.2 Movement Tasks 117 5.3.2.1 Hinge Opening Movement 118 5.3.2.2 Protrusive and Lateral Movements: EMG Based-Muscle Activation 118 5.3.2.3 Lateral Movements: Muscle Activation According to Muscle Length 120 5.4 Results 122 5.4.1.1 Operator Guided Hinge Opening 122 5.4.1.2 Protrusion 122 5.4.1.3 Lateral Movements 124 5.4.1.3.1 EMG-Based Muscle Activation 124 5.4.1.3.2 Muscle Length-based Activation 131 5.5 Discussion 137 5.5.1 Jaw Modelling 137 5.5.2 Muscle-driven Jaw Motion 138 5.6 Conclusions 143 6 THE EFFECT OF THE LATERAL TEMPOROMANDIBULAR LIGAMENT AND CAPSULE ON JAW MOTION 144 6.1 Abstract 144 6.2 Introduction 145 6.3 Methods 147 6.3.1 Capsular Morphology 148 6.3.2 Mandibular Movement 150 6.4 Results 153 6.4.1 Opening Movement 157 6.4.2 Protrusive Movement 160 vi 6.4.3 Contralateral Movement 162 6.4.4 Ipsilateral Movement 163 6.5 Discussion ; 168 6.5.1 Assumptions 168 6.5.2 The Role of the Lateral Capsular Wall 169 6.6 Conclusions 174 7 A MODEL OF THE PASSIVE TENSION PROPERTIES OF THE MASSETER MUSCLE 180 7.1 Abstract 180 7.2 Introduction 181 7.3 Methods 183 7.3.1 Complex Muscle Models (Models CU & CD) 183 7.3.1.1 Complex Muscle Model Components 185 7.3.1.1.1 Muscle Thickness 185 7.3.1.1.2 Tendon Properties 191 7.3.1.1.3 Fibre Properties 191 7.3.2 Simple Muscle Model (Model S) 193 7.3.2.1 Simple Muscle Model Components 193 7.3.3 Muscle Dynamics 195 7.3.4 Mandibular Movement 195 7.4 Results 196 7.4.1 Jaw operiing 196 7.4.1.1 Resultant forces at superior (2ygomatic) muscle attachment 196 7.4.1.2 Fibre and tendon dynamics 197 7.4.2 Contralateral Jaw Movement 207 7.4.2.1 Resultant forces at superior (zygomatic) muscle attachment 207 7.4.2.2 Fibre and tendon dynamics 212 7.5 Discussion • 213 7.5.1 Modelling 213 7.5.2 Resultant Muscle Forces 219 7.5.3 Muscle Component Properties 220 vii 7.6 Conclusions 222 8 GENERAL DISCUSSION 224 8.1 Jaw modelling 224 8.2 Jaw dynamics 227 8.2.1 Passive constraints 227 8.2.1.1 Jaw muscles , 227 8.2.1.2 Lateral capsular wall 229 8.2.2 Active constraints (muscle) 230 8.2.3 Condylar loading 231 9 GENERAL SUMMARY & CONCLUSIONS 233 10 FINAL COMMENTS & FUTURE DIRECTIONS 235 11 BIBLIOGRAPHY 238 viii LIST OF FIGURES Page Figure 1 Anterolateral view of the basic model showing the muscle group actuators' lines of action 43 Figure 2 Temporomandibular joint analogues 46 Figure 3 Incisal point envelope of border movements produced by the kinematically-driven model 48 Figure 4 Generic passive muscle length-tension curve utilised for all muscle group actuators in (A) previous studies, and (B) current study 57 Figure 5 Comparison of rest position incisal gape for passive muscle tension function exponents between 10 and 0.0001 58 Figure 6 Effect of simple and expanded linear jaw-opener muscle activity on incisor opening pathway for 40° condylar guidance models 70 Figure 7 Effect of simple and expanded linear jaw-opener muscle activity on incisor opening pathway for 25° condylar guidance models , 71 Figure 8 Effect of simple linear, unilateral jaw-opener muscle activity (the left lateral pterygoid actuator has been removed) on incisor opening pathway for 40° condylar guidance model 72 Figure 9 Jaw-opener tensions plotted against time for 40° condylar guidance models: 40LF&C40XF 73 Figure 10 Jaw-opener tensions plotted against time for 25° condylar guidance models: 25LF & 25XF.
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