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1HF‘LES

llBRARY
Michigan State
University

This is to certify that the

thesis entitled

THREE-DIMENSIONAL KINEMATICS OF THE EQUINE
TEMPOROMANDIBULAR JOINT

presented by

Stephanie Julie Bonin

has been accepted towards fulfillment
of the requirements for

MS . Mednnical Engineering
degree 1n

 

M
1

/ Major pr<%essor

Date 8/29/0/

0-7639 MS U is an Afﬁrmative Action/Equal Opportunity Institution

 

PLACE IN RETURN BOX to remove this checkout from your record.
To AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6/01 cJClRC/DateDuepesop. 15

THREE-DIMENSIONAL KINEMATICS OF THE
EQUINE TEMPORAL MANDIBULAR JOINT

By

Stephanie Julie Bonin

A THESIS

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Mechanical Engineering

2001

ABSTRACT

THREE-DIMSIONAL KINEMATICS OF THE
EQUINE TEMPORAL MANDIBULAR JOINT

By

Stephanie Julie Bonin

Topics in equine medicine related to the temporomandibular joint (TMJ) receive far less
attention than other branches such as lameness, infectious disease and reproduction.
Problems with the TMJ can affect a horse’s ability to chew and properly digest its food
and to perform as an athlete. The anatomy of the equine dentition is such that the
constructs of the teeth highly inﬂuence the overall motion of the mandible and the
grinding capacity during the chewing cycle. Consequently, regular dental exams and
treatments are essential to the overall health of the animal. As in most branches of
medicine, it is important to ﬁrst understand normal function prior to analyzing
pathologies. This study examines the normal chewing pattern of seven horses while
chewing two different feed types: hay and pellets. Retro-reﬂective spherical markers
were adhered to the horse’s skull and mandible and a Motion Analysis System recorded
the marker locations as the horses chewed hay and pellets. The data were processed with
customized software and the three-dimensional displacement and rotations, described as
pitch, roll, and yaw, of the mandible relative to the skull were computed. In addition, a
virtual tracking marker was created on the mandible and tracked relative to the skull. The
mandible was found to have a signiﬁcantly greater range of motion while chewing hay
versus pellets. The mandibular velocity while chewing hay versus pellets was not

signiﬁcantly different.

Copyﬁghtby
Stephanie Bonin

2001

DENTAL DILEMMA
By Dale Jeffrey

When I was young my teeth came in
They got sharp edges that stole my grin
Somehow they didn’t match quite right
And now I’ve got an overbite.

As if these problems weren’t enough
My wolfers made my cheeks so rough

And aﬁer they became so sore
They couldn’t drag me through the door

There was not a bit that I would take
Nor any rider I could shake

So there I stood within my stall

No one would help me through it all

My caps came in and stuck so tight
They say I colicked in the night
And now I have the wavy mouth

I hear they’ll ship me to the south

So. ..
If you don’t want to end up like me
Your equine dentist, you should see

 

ACKNOWLEDGMENTS

I would like to thank my co-advisor, Dr. Hilary M. Clayton, for her supervision

throughout the duration of this project and guidance during the writing of this thesis.

I am grateful for the contributions of my co-advisor Dr. Brian Feeny and committee
member Dr. Alan Haddow. Thank you for being part of my committee and advising me

during the writing of this document.

I greatly appreciate the assistance of Dr. Thomas Johnson, whose desire to improve the

quality of horse’s lives lead to this research.

I would also like to express my deepest gratitude to Mr. Joel Lanovaz, whose input made
this research possible. Thank you for the valuable contributions and guidance made

throughout this project.

Finally, I would like to thank my husband, Dr. Hooman Rezaei for his patience and

understanding throughout the time required to complete this thesis.

TABLE OF CONTENTS

LIST OF TABLES ................................................................................ viii
LIST OF FIGURES ................................................................................ ix
CHAPTER 1
1. INTRODUCTION .............................................................................. 1
1.1 Equine Dental Evolution .................................................................. 1
1.2 Common Dental Malocclusions .......................................................... 4
1.3 Dental Health and Performance ........................................................................... 8
1.4 Anatomy of the Ternporomandibular Joint ....................................... 10
1.4.1 Bones of the Skull .............................................................. 11
1.4.2 Muscles of Mastication ........................................................ 12
1.5 Evaluation of TMJ Motion ................................................................ 13
1.5.1 Equine Studies ................................................................... 13
1.5.2 Human Studies .................................................................. 19
1.6 Kinematic Analysis .............................................................................. 19
1.7 Motion Analysis System ........................................................................ 21
1.8 Research Objectives ............................................................................. 22
CHAPTER 2
2. MATERIALS AND METHODS .............................................................. 23
2.1 Subjects ..................................................................................... 23
2.2 Equine Preparation ................................................................... 23
2.3 Equipment Set-Up .................................................................... 25
2.4 Data Collection Procedure ........................................................... 26
2.4.1 Standing Files .................................................................. 26
2.4.2 Tracking Files .................................................................. 26
2.5 Data Processing ............................................................................................ 28
2.5.1 Coordinate Transformations ................................................................ 30
2.5.2 Coordinate System Development ........................................................ 35
2.5.3 Euler Angles ........................................................................................ 37
2.5.4 Midline-Mandible Marker Development ............................................ 40
2.6 Data Post-Processing ................................................................. 43
2.6.1 Cycle Deﬁnition ............................................................... 43
2.6.2 Data Normalization ........................................................... 43
2.6.3 Processing Midline-Mandibular Marker ................................... 44
2.6.4 Processing Mandibular Coordinate System ............................... 44
2.6.5 Processing Euler Angle Data .............................................................. 45
2.6.6 Statistical Analysis .............................................................................. 45
CHAPTER 3
3. RESULTS ................................................................................................................... 47
3.1 General Midline-Mandibular Marker Motion .................................................... 47

3.2 Mandible Coordinate System Displacement ...................................................... 52

3.3 Euler Angles ....................................................................................................... 53
CHAPTER 4
4. DISCUSSION ............................................................................................................ 65
4.1 Signiﬁcance of Marker Placement ..................................................................... 65
4.2 Diet Effects on Dentition ................................................................................... 70
4.3 Mandibular Euler Angles During Chewing ....................................................... 73
4.4 Mandibular Coordinate System Displacement .................................................. 75
4.5 Midline-Mandibular Marker Displacement ....................................................... 76
4.6 Comparisons to Previous Work ......................................................................... 77
4.6.1 Lateral Mandibular Displacement (Y-displacement) ......................... 77
4.6.2 Mandibular X- and Z- Displacement .................................................. 81
4.6.3 Mandibular Chewing Velocity and Frequency ................................... 81
4.6.4 Mandibular Coordinate System Translation and Rotation .................. 82
4.6.5 Human Studies .................................................................................... 83
CHAPTER 5
5. CONCLUSIONS AND RECOMMENDATIONS .................................................... 84
APPENDIX A
Location of midline-mandibular marker relative to skull coordinate system
viewed in all three planes for all horses ....................................................................... 87
APPENDIX B
Location of mandibular coordinate system relative to skull coordinate system
viewed in all three planes for all horses ....................................................... 109
APPENDIX C
Mandibular Euler angles for all horses ...................................................... 131
BIBLIOGRAPHY ................................................................................ 146

vii

LIST OF TABLES

Table 1: Description of horses used in the study .......................................................... 23
Table 2: Description of feed types ................................................................................ 27

Table 3: Mean (SD) x,y, and z displacement of the midline-mandibular
marker for each horse while chewing hay and pellets ....................................... 50

Table 4: Mean area encompasses by each cycle in the z-y plane

for hay and pellets ........................................................................................... 51
Table 5: Mean absolute velocity for all horses for each sample ................................... 51
Table 6: Mean cycle duration for all horses for each feed sample ................................ 52

Table 7: Mean (SD) x,y, and z displacement of the mandible coordinate
system relative to the skull coordinate system for each horse
while chewing hay and pellets ........................................................................... 53

Table 8: Mean range of Euler angles for all horses chewing hay and pellets ............... 54

viii

LIST OF FIGURES

Figure 1: Schematic of a cheek tooth’s anatomy .......................................................... 3
Figure 2: Common Malocclusions ................................................................................ 8
Figure 3: Bones of the Equine skull ............................................................................. 12
Figure 4: Mechanical recorded utilized to trace grinding patterns ............................... 14
Figure 5: Varying grinding patterns while chewing grass (Gras),

hay (Hafer), and bran (Kleie) ........................................................................... 15
Figure 6: Chewing cycle of a horse reproduced from video recordings ...................... 16
Figure 7: Path of mandible during the chewing cycle ................................................. 16
Figure 8: Upper and lowed dental arcades .................................................................. 18
Figure 9: Locations of the skin markers ...................................................................... 24
Figure 10: Camera set-up ............................................................................................ 25
Figure 11: Horse standing in calibrated volume, chewing pellet samples .................. 27
Figure 12: Location of skull and mandible coordinate systems .................................. 30
Figure 13: Two Cartesian reference frames ................................................................ 31
Figure 14: Translation and rotation of a reference frame ............................................ 34
Figure 15: Description of mandibular rotations .......................................................... 39
Figure 16: Location of Midline-Mandibular Marker ................................................... 41
Figure 17: The three planes the data are described in ................................................. 55

Figure 18:

Normalized midline-mandibular marker location in the

z-y plane from one chewing cycle viewed ﬁom the front of a horse #1
chewing on the right ......................................................................................... 56

Figure 19: Normalized midline-mandibular marker location from one chewing
cycle viewed in the z-y plane of a horse #4 chewing on the left ...................... 57

Figure 20: Normalized midline-mandibular marker from one chewing cycle
of hay (thicker line) and pellets (thinner line) from horse #5 .......................... 58

Figure 21: Characteristic chewing patters of the normalized midline-
mandibular marker location from one chewing cycle of horse #4
chewing on the left, viewed in the z-x plane .................................................... 59

Figure 22: Characteristic chewing patters of the normalized midline-
mandibular marker location from one chewing cycle of horse #4
chewing on the left, viewed in the x-y plane .................................................... 60

Figure 23: Location of mandible coordinate system during one sample
chewing cycle from horse #4 viewed in the z-y plane ..................................... 61

Figure 24: Location of mandible coordinate system during one sample chewing
cycle from horse #4 viewed in the z-x plane .................................................... 62

Figure 25: Location of mandible coordinate system during one sample chewing
cycle from horse #4 viewed in the x-y plane .................................................... 63

Figure 26: Euler angles for one trial from horse #1 chewing hay:
pitch (top), roll (middle), and yaw (below) ...................................................... 64

Figure 27: Schematic of enamel ridges for a left cheek tooth while chewing
on the left. Black = upper molar, Grey = lower molar (a) maximum
lateral excursion (start of grinding phase) (b) mid grinding phase
(0) end of grinding phase (resting position) ..................................................... 80

Figure 28: z-y location of midline-mandibular marker for horse #1
chewing on the right ................................................................... 88

Figure 29: z-x location of midline-mandibular marker for horse #1
chewing on the right ................................................................... 89

Figure 30: x-y location of midline-mandibular marker for horse #1
chewing on the right ................................................................... 90

Figure 31: z-y location of midline-mandibular marker for horse #2
chewing on the left ..................................................................... 91

Figure 32: z-x location of midline-mandibular marker for horse #2
chewing on the left ..................................................................... 92

Figure 33: x-y location of midline-mandibular marker for horse #2
chewing on the left ..................................................................... 93

Figure 34: z-y location of midline-mandibular marker for horse #3
chewing on the left ..................................................................... 94

Figure 35: z-x location of midline-mandibular marker for horse #3
chewing on the left ..................................................................... 95

Figure 36: x-y location of midline-mandibular marker for horse #3
chewing on the left ..................................................................... 96

Figure 37: z-y location of midline-mandibular marker for horse #4
chewing on the left ..................................................................... 97

Figure 38: z-x location of midline-mandibular marker for horse #4
chewing on the left ..................................................................... 98

Figure 39: x-y location of midline-mandibular marker for horse #4
chewing on the left ..................................................................... 99

Figure 40: z-y location of midline-mandibular marker for horse #5
chewing on the left .................................................................... 100

Figure 41: z-x location of midline-mandibular marker for horse #5
chewing on the left .................................................................... 101

Figure 42: x-y location of midline-mandibular marker for horse #5
chewing on the left .................................................................... 102

Figure 43: z-y location of midline-mandibular marker for horse #6
chewing on the left .................................................................... 103

Figure 44: z-x location of midline-mandibular marker for horse #6
chewing on the left .................................................................... 104

Figure 45: x-y location of midline-mandibular marker for horse #6
chewing on the left .................................................................... 105

Figure 46: z-y location of midline-mandibular marker for horse #7
chewing on the left .................................................................... 106

Figure 47: z-x location of midline-mandibular marker for horse #7
chewing on the left .................................................................... 107

Figure 48: x-y location of midline-mandibular marker for horse #7
chewing on the left ................................................................... 108

Figure 49: z-y location of mandibular coordinate system for horse #1

xi

chewing on the right ................................................................... 1 10

Figure 50: z-x location of mandibular coordinate system for horse #1
chewing on the right ................................................................... 1 1 1

Figure 51: x-y location of mandibular coordinate system for horse #1
chewing on the right ................................................................... l 12

Figure 52: z-y location of mandibular coordinate system for horse #2
chewing on the left .................................................................... 1 13

Figure 53: z-x location of mandibular coordinate system for horse #2
chewing on the left .................................................................... 1 14

Figure 54: x-y location of mandibular coordinate system for horse #2
chewing on the left .................................................................... 1 15

Figure 55: z—y location of mandibular coordinate system for horse #3
chewing on the left .................................................................... 1 16

Figure 56: z-x location of mandibular coordinate system for horse #3
chewing on the left .................................................................... 1 17

Figure 57: x-y location of mandibular coordinate system for horse #3
chewing on the left .................................................................... 1 18

Figure 58: z-y location of mandibular coordinate system for horse #4
chewing on the left .................................................................... l 19

Figure 59: z-x location of mandibular coordinate system for horse #4
chewing on the left .................................................................... 120

Figure 60: x-y location of mandibular coordinate system for horse #4
chewing on the left .................................................................... 121

Figure 61: z-y location of mandibular coordinate system for horse #5
chewing on the right ................................................................... 122

Figure 62: z-x location of mandibular coordinate system for horse #5
chewing on the right ................................................................... 123

Figure 63: x-y location of mandibular coordinate system for horse #5
chewing on the right ..... . .............................................................. 124

Figure 64: z-y location of mandibular coordinate system for horse #6
chewing on the right ................................................................... 125

xii

Figure 65: z-x location of mandibular coordinate system for horse #6

chewing on the right ................................................................... 126
Figure 66: x-y location of mandibular coordinate system for horse #6

chewing on the right ................................................................... 127
Figure 67: z-y location of mandibular coordinate system for horse #7

chewing on the right ................................................................... 128
Figure 68: z-x location of mandibular coordinate system for horse #7

chewing on the right ................................................................... 129
Figure 69: x-y location of mandibular coordinate system for horse #7

chewing on the right ................................................................... 130
Figure 70: Euler angles for horse #1 while chewing hay on the right .................. 132
Figure 71: Euler angles for horse #1 while chewing pellets on the right ............... 133
Figure 72: Euler angles for horse #2 while chewing hay on the left .................... 134
Figure 73: Euler angles for horse #2 while chewing pellets on the left. . . .....l35
Figure 74: Euler angles for horse #3 while chewing hay on the left .................... 136
Figure 75: Euler angles for horse #3 while chewing pellets on the left ................ 137
Figure 76: Euler angles for horse #4 while chewing hay on the left .................... 138
Figure 77: Euler angles for horse #4 while chewing pellets on the left ................ 139
Figure 78: Euler angles for horse #5 while chewing hay on the right .................. 140
Figure 79: Euler angles for horse #5 while chewing pellets on the right. . . . . .....141
Figure 80: Euler angles for horse #6 while chewing hay on the right .................. 142
Figure 81: Euler angles for horse #6 while chewing pellets on the right ............... 143
Figure 82: Euler angles for horse #7 while chewing hay on the right .................. 144
Figure 83: Euler angles for horse #7 while chewing pellets on the right ............... 145

xiii

1. Introduction:

Prior to discussing modem-day equine dentistry, it is important to understand how and
why the horse’s dentition evolved to its present state. In this section, the evolution of
equine dentition will be brieﬂy discussed, followed by a description of common
malocclusions. A description of the anatomy of the TMJ, the skull’s bones, and muscles
of mastication will follow. Previous equine and human studies that examined the motion
of the TMJ will be mentioned next. Finally, a brief discussion of kinematic analysis
techniques, a description of the motion capture system, and a statement regarding the

research objectives will complete the chapter.

1.] Equine Dental Evolution:

The evolutionary developments that lead to the modern horse Equus caballus began
during the Eocene Epoch, which lasted from about 54 million to 38 million years ago.
During the early Eocene the ﬁrst ancestral horse appeared, a hoofed, browsing mammal
known technically as Hyracotherium but more commonly called eohippus, the "dawn
horse." This animal lived on succulent plants that caused little dental wear on its short-
crowned teeth. As the years went by, climatic changes resulted in vegetation changes and
the descendants of Hyracotherium evolved to adapt to a coarse, grassy diet (Baker and

Easley, 1999).

During the remainder of the Eocene, the prime evolutionary changes were in dentition,
which appear abruptly in the fossil record. Orchippus, a genus ﬁ'om the middle Eocene,
and Epihippus, a genus from the late Eocene, resembled eohippus in size and limb
structure, but the dentition was quite different. The cheek teeth, comprising the four
premolars and the three molars found in each half of both jaws, were undergoing changes.
In eohippus the premolars and molars were clearly distinct, the molars being larger. In
Orohippus the fourth premolar had become similar to the molars, and in Epihippus the
second, third, and fourth premolars had become molar-like. Modern day horses have
retained this pattern. The six functional cheek teeth, consisting of the second, third, and
fourth premolars and the three molars, are similar in size and shape. This ﬁrst premolar
has become vestigal. It is sometimes present as the “wolf” tooth, in the upper dental

arcade, but is essentially non-functional.

In addition to these morphological changes, the individual cusps that characterized the
cheek teeth of eohippus had been replaced in Epihippus by a system of continuous crests
or ridges running the length of the molars and premolars (Encyclopedia Britannica, 2000).
As a result, the outer surface of the teeth was no longer covered entirely by enamel;
instead a folded layer of cement, enamel, and dentin was exposed to the occlusal surface

(Figure 1).

cement

dentin

enamel

 

 

functional
crown

reserve
C POW”

 

pulp cavity

 

 

 

Figure 1: Schematic of a cheek tooth’s anatomy

These calciﬁed tissues wear at different rates (enamel slowest, dentin and cementum
fastest) creating a permanently irregular occlusal surface that is advantageous in the
grinding of coarse ﬁbrous foodstuffs and acts as a self-sharpening mechanism (Baker and
Easley, 1999). These changes, which represent adaptations to a more specialized grazing

diet, were retained by all subsequent ancestors of the modern horse.

Grass is much coarser than succulent leaves and requires a different kind of tooth
structure. Grass contains abrasive silicates, both within the plant and in the soil attached
to the roots and lower stems. As equine predecessors increased in size, they were
required to forage for longer periods of time to ingest sufticient nutrients to support their
larger body mass and the food was ground into smaller particles for more efﬁcient
digestion. The changing requirements placed additional demands on the cheek teeth,
which developed larger, stronger crests and became adapted to the side-to-side motion of
the lower jaw necessary to grind grass blades. Each tooth progressed from being low-
crowned (brachydont) to developing an extremely long crown (hypsodont), most of
which, in the young animal, was buried beneath the gum line. As grinding wore down the
exposed surface, some of the reserve crown grew out. This high-crowned tooth structure
assured the animal of having an adequate grinding surface throughout its normal life
span. Adaptations in the digestive tract must have occurred as well, but the organs of
digestion are not preserved in the fossil record. In modern day horses, the permanent
cheek teeth erupt at a rate of 2-3 min/year, which is similar to the rate of attrition on the
occlusal surface of the tooth, provided the horse regularly consumes a ﬁbrous diet such as

grass rather than high levels of concentrate food (Baker and Easley, 1999).

1.2 Common Dental Malocclusions:

A horse’s teeth erupt constantly throughout its lifetime. The coarse, ﬁbrous nature of the
horse’s diet wears the surface of the teeth, but the wear patterns are not always

symmetrical and dental pathologies frequently occur. Malocclusions, or the improper

position and contact between teeth, lead to inefﬁcient chewing, bit discomfort, excessive
wear and premature loss of teeth. Many horses will not show overt symptoms of dental
problems until it is too late to treat them successﬁrlly. Malocclusions of the molars
include hooks, ramps, enamel points, sheared molar table, wave complexes, accentuated

transverse ridges, and periodontal pockets.

Hooks can develop at the rostral or caudal ends of the molar table. Rostral hooks are
dominant upper front premolars overhanging the rostral edge of the lower premolars.
They may develop as a result of a horse born with an overbite or they may be a secondary
result from molar malocclusions that force the jaw out of alignment (Johnson, 2000).
Caudal hooks are dominant lower or upper last molars overhanging the opposing molar.
They may develop as a result of a horse born with an underbite or they may be a
secondary result from molar malocclusions that force the jaw out of alignment (Johnson,
2000). Both conditions prevent horses from chewing freely from side to side, resulting in
improper and excessive molar wear. They can cause extreme discomfort when the
position of the head is changed during riding or from interaction with the bit, and the

sharp molar points can lacerate soft tissues (Baker and Easley, 1999, Johnson, 2000).

Excessive height of the lower second premolar characterizes a ramp. This condition may
occur when the upper second premolar deciduous tooth is retained, preventing normal
growth of the permanent premolar (Johnson, 2000). They may also arise from a tooth

reduction without correcting the opposing tooth. Ramps also prevent horses from

chewing freely from side to side, cause severe discomfort with the bit, and can force the

lower jaw forward over time, resulting in an underbite (Johnson, 2000).

Enamel points are sharp points that generally form on the buccal (cheek) side of the upper
molars and lingual (tongue) side of the lower molars (Baker and Easley, 1999, Johnson,
2000). They develop over time as the horse reduces the lateral excursion of the mandible
during chewing, resulting in the unopposed edge of the tooth getting longer. The unwom
enamel forms razor sharp points. Sometimes this progresses to a sheared molar table,
which is an extreme angulation of the chewing surface of the molars as seen from the
front (Hayes, 1968, Johnson, 2000). This is a more severe condition than sharp enamel
points since it precludes lateral motion of the mandible. This becomes a vicious cycle

resulting in poor utilization of feed.

Wave complexes are characterized by a series of convex and concave changes of the
crowns and occlusal surfaces of the cheek teeth with a reciprocal concave and convex
changes on the opposing arcade (Baker and Easley, 1999) resulting in an uneven
“wavelike” appearance. This condition often occurs secondary to other malocclusions
such as retained deciduous caps, missing teeth, hooks, ramps, etc. Wave complexes
cause gradual excessive wear to many molars, resulting in prematurely worn out teeth,
periodontal pocketing, decay, and loss of teeth (Johnson, 2000). The horse is prevented

from chewing freely from side to side and properly grinding its food.

Enlarged ridges that run across chewing surfaces of molars are accentuated transverse
ridges and can result from a shift in jaw alignment. Ridges develop as a result of a harder
area in one tooth wearing a soft area in an opposing tooth. This condition can also
develop if a horse is not chewing with proper lateral excursion. Excessive wear to
opposing molars, reduced front to back motion of the lower jaw, and severe periodontal

disease can result (Johnson, 2000).

Periodontal pockets develop when gum disease around a tooth allows a space to develop
between the tooth and the surrounding gum. Food collects in the resulting pocket and
leads to infection, abscesses, and bone erosion around the teeth, which lose their stability

and may fall out (Johnson, 2000). Figure 2 depicts some of the above malocclusions.

  

CAUDAL

   
   

page.“ STEPPED RAM?
mourn

OVERJET

Figure 2: Common Malocclusions

Proper and regular dental treatment can prevent and correct many of these malocclusions.

1.3 Dental Health and Performance:

In order to wear the occlusal surfaces of the teeth sufﬁciently, the mandible must undergo

adequate lateral excursion. When the teeth do not completely abrade against each other,

malocclusions, such as sharp enamel point, hooks, and ramps can develop, which can

exacerbate the problem by further preventing lateral excursion. This self-propagating
cycle can lead to inefﬁcient chewing, poor nutrition, bit discomfort, excessive wear and
premature loss of teeth. Many horses will not show symptoms of dental problems until it
is too late. In addition, horses experiencing oral pain will not perform up to their best

abilities.

Performance horses face further anomalies as they are required to wear a bridle, which
includes a bit in their mouth and cavesson (leather strap) ﬁtted snug around their nose to
aid in keeping the mouth shut. Pain can result from the bit making harsh and abrupt
contact with malocclusions at the rostral end of the cheek teeth and the cavesson prevents

the jaws from opening to avoid contact and alleviate the pain.

As a horse is ridden, the rider often changes the position of the horse’s head. As the head
moves ﬁ'om a somewhat horizontal position to an orientation that is more perpendicular
to the ground, the lower jaw may slide relative to the upper jaw. In cases where severe
wave mouth or hooks exist, the lower jaw cannot easily slide due to the cheek teeth
interfering with each other. In order to comfortably orient the head in the desired
position, the mouth must open to allow the lower jaw to slide, however, with a cavesson
ﬁtted snuggly over the nose, the jaws are unable to open. Consequently, pain can develop
at the TMJ, resulting in head tossing, teeth grinding, and tail swishing, which are often

considered training problems rather than medical problems.

1.4 Anatomy of the Temporomandibular Joint:

The temporomandibular joint is classiﬁed as a synovial, condylar joint, formed by the
condylar process of the mandible that engages with the articular tubercle of the temporal
bone. A meniscal cartilage compensates for incongruencies between the two articular
surfaces (Rosenstein et al., 2001). The joint capsule it tight and reinforced by an
indistinct lateral ligament and an elastic posterior ligament (Sisson and Grossman, 1975).
A joint complex, as depicted in Figure 3, exists on each side of the skull with
independent joint capsules, but the whole arrangement is regarded as constituting a single
condylar joint (Dyce et. al., 1987). Movement on one side must be accompanied by a
movement, not necessarily identical, on the other side (Dyce et al., 1987). Between the
articular surfaces of the mandible and the temporal bone lies a ﬁbrous articular disc that
divides the joint cavity into upper and lower compartments, the former being more
spacious (Sisson and Grossman, 1975). The complex motion of the joint can be resolved
into simpler components; a hinge movement occurs in the lower compartment between
the mandible and the disk, while translation of the mandible relative to the skull occurs at
the upper compartment. In species where the mandibular movement is simple, such as a
dog, the disk is rather thin and poorly developed. In species where lateral grinding
movements predominate, the mandibular head is larger, the surface more plateau-like,
and the disk thicker as in most herbivores (Dyce et al., 1987). Herbivores employ the
cheek teeth for grinding ingested food and the active grinding movement is preceded by
lateral displacement. The temporomandibular joint of these animals is situated high

above the occlusal plane and the lower teeth are drawn forward over the opposing upper

teeth as they approach. This contributes a grinding component that is absent when the

joint and occlusal surfaces are more nearly level (Dyce etal., 1987).

1.4.1 Bones of the Skull:

The temporal bone is one of ﬁfteen bones that articulate to form the skull. It forms the
greater part of the lateral wall of the cranium and articulates with the zygomatic, occipital,
parietal, frontal, and basisphenoid bones by rigid joints called sutures (Figure 3). It also
articulates with the mandibular condyle, and the hyoid apparatus. The temporal bone
consists of three distinct parts: squamous, tympanic, and petrous (Dyce et al., 1987). The
squamous portion of the temporal bone articulates with the mandible at the
temporomandibular joint. The mandible is the largest bone of the equine face. The left
and right mandibles are ﬁrmly joined at the mandibular symphysis that fuses in the foal at

2 to 3 months (Baker and Easley, 1999).

 

A. Incisive E. Zygomatic J. Temporal

B. Nasal F. Frontal K. Sphenoid
C. Maxilla G. Parietal L. Palatine
D. Lacrimal H. Interparietal M. Mandible

I. Occipital

Figure 3: Bones of the Equine skull

1.4.2 Muscles of Mastication:

Six muscle pairs are utilized during chewing. The masseter, which aids in closing the

mouth, originates from the facial crest and the zygomatic arch and inserts on the rarnus of

the mandible. The temporalis originates at the temporal fossa and inserts at the coroniod

process of the mandible and acts in closing the mouth. The media] and lateral pterygoids
close the mouth and move the mandible rostrally and laterally. They originate from the
pterygoid process of the basisphenoid bone, and insert on the medial surface of the
mandible. The digastricus muscle, which opens the mouth, originates from the jugular
process of the occipital bone and inserts on the ventral border of the mandible. Finally,
the occipitomandibularis, another muscle that opens the mouth, originates from the
jugular process of the occipital bone, and inserts on the caudal border of the mandible.
All muscles of mastication are innervated by the mandibular branch of the trigerrrinal (V)
nerve except for the digastricus, which has dual innervation from the facial (VII) and
trigeminal (V) nerves and the occipitomandibularis, which is supplied by the facial (VII)

nerve (Sisson and Grossman, 1975).

1.5 Evaluation of TMJ Motion:

Existing studies of TMJ motion in horses and humans are reviewed in this section.

1.5.1 Equine Studies:

Chewing is based upon the repetition of a cyclical movement that results from the

coordinated rhythmic contraction of all the muscle groups associated with the opening

and closing of the jaws. In studies of the chewing cycle in many species it was found

that, with the exception of man, mammals have consistent chewing patterns - consistent

l3

both individually and as a species (Baker and Easley, 1999). Few studies exist on

qualifying the three-dimensional motion of the equine TMJ.

In 1941, Leue developed a mechanical recorder that attached to the upper and lower jaws

of horse’s with a stationary notepad and a pen the followed the motion of the mandible

(Figure 4).

 

Figure 4: Mechanical recorder utilized to trace grinding patterns
(Leue, 1941, cited by Becker, 1962)

Dixon (2000) stated the lateral excursion values from Leue’s study were 60 mm, 38 mm,

and 23 mm while chewing grass, oats, and bran respectively. Leue, however, did not

report these values and the location that these measurements were made is not speciﬁed

(Figure 5).

 

Figure 5: Varying grinding patterns while chewing grass (Gras), hay (Hafer),
and bran (Kleie) (Leue, 1941, cited by Becker, 1962)

Leue proposed that bundles of ﬁbrous food such as hay or grass could readily be
maintained on the occlusal surface of the mandibular cheek teeth as they moved laterally
to their full extent, thereby allowing a complete horizontal grinding movement.
However, just a limited quantity of particulate food, such as bran, could be retained on
the narrow mandibular occlusal surface. Therefore, a primary vertical mandibular
movement, with minimal lateral excursion, was required to maintain particulate food
between the occlusal surfaces. The lack of lateral excursion allows the development of
enamel overgrowths. Diets high in concentrates also greatly limit the length of time
horses chew forages and so further predispose to such enamel overgrowths (Leue, 1941,

cited by Dixon et al., 2000).

Baker and Easley (1999) conducted a two-dimensional video analysis of the equine

masticatory movements. Their results corresponded to the general masticatory cycle of

15

herbivorous mammals with the chewing cycle being divided into three phases according
to the relative displacement of the mandible: the opening stroke (0), the closing stroke
(C), and the power stroke (P). Figure 6 depicts isolated frames from a video recording of
equine mastication and Figure 7 shows the positional changes of the mandible. Note that
frames 1- 4 represent the opening stroke, frames 5-6 represent the closing stroke, and

frames 7-10 represent the power stroke.

 

Figure 6: Chewing cycle of a horse reproduced from video recordings
(Baker and Easley, 1999, reproduced with permission).

6,4,??9
£2
)10}

Figure 7: Path of mandible during the chewing cycle
(Baker and Easley, 1999, reproduced with permission).

l6

It is evident that Baker and Easley observed the chewing cycles from the front of the
horse, however, they did not deﬁne the speciﬁc plane that the motion was observed in. In
addition, the motion was tracked by observing how a point on the lower lip displaced
relative to a point on the upper lip. The lips consist of highly mobile soft tissue and
cannot be classiﬁed as rigid bodies. Therefore, movements of the lips do not accurately
represent mandibular motion, though they may indicate the general pattern of movement.
In a study by Collinson (1994), the chewing frequency was measured using
electromyography in four horses chewing food classiﬁed as low, medium, and high ﬁber.
The frequency ranged from 1.14 Hz while chewing food with high ﬁber content to 1.16
Hz while chewing food with low ﬁber content. Collinson also measured the absolute
velocity of the fourth premolar, which ranged from 85 mm/sec while chewing high-ﬁber
food to 104 min/sec while chewing low-ﬁber food. Incisor displacement was reported to

be 44-45 mm.

The studies of Leue (1941) and Baker and Easley (1999) were two-dimensional. Previous

studies of three-dimensional equine chewing motion have not been discovered.

The arrangement of the teeth within the upper and lower jaws is such that the lateral
outward curve of the upper dental arcade is not fully accommodated by the conformation
of the lower arcade, i.e. the lower arcade is straighter and the distance between the left

and right arcades is less in the mandible than in the upper jaw (Figure 8).

l7

 

ii”; ' a”;

'--* cg.
~

 

 

Figure 8: Upper and lower dental arcades

As a consequence of the discrepancy in width between the upper and lower dental
arcades, the mandible must move a considerable distance laterally to make complete
occlusal contact across the width of the teeth in the upper arcade. Complete occlusal

contact is necessary to ensure that the entire molar table receives even and adequate wear.

18

1.5.2 Human Studies:

Human studies have been performed to evaluate the three-dimensional TMJ motion.
Techniques utilized include magnetic resonance imaging (MRI) to acquire sequential
images of the joint capsule during opening and closing of the mouth (Chen and
Buckwalter, 1992, Koolstra and Van Eijden, 1992), an optoelectronic system that tracks
light-emitting diodes (Zhang et al. 1995, Ostry et al. 1997, Gallo et al., 2000), and
magnetometers in which the displacement of magnets on the incisors is detected and
recorded (Plesh et al., 1993). Computed tomography allows three-dimensional
examination of the TMJ and has been used primarily for morphological examination and
to develop mathematical models of the joint (Christiansen et al. 1987, Paz et al. 1990,
Raustia et al., 1990). Similar techniques (radiographic, ultrasound, computed
tomography, scintigraphy, and magnetic resonance imaging) have been applied in studies
of the equine TMJ, primarily for anatomical purposes and not for motion analysis
(Patterson et al., 1989, Warmerdam et al., 1997, Weller et al., 1999, Rosenstein et al.,

2001).

1.6 Kinematic Analysis:

A complete understanding of joint kinematics is important in understanding the etiology,
pathology, diagnosis, and treatment of joint disorders resulting from injury or disease, in

the design of better prosthetic devices, and in the general study of locomotion (Grood and

19

Suntay, 1983). In order to evaluate joint motion, a set of coordinate systems needs to be
established in the segments proximal and distal to the joint. In 1983, Grood and Suntay
developed a joint coordinate system that provides a simple geometric description of the
three-dimensional rotational and translational motion between rigid bodies. Their
coordinate system was applied to the knee and the joint motions were described in a way
that provides clinical signiﬁcance for physicians and orthopaedic surgeons. Joint
coordinate systems are created by using markers placed on key anatomical locations such
that the axes of the coordinate systems are aligned with anatomical axes of the body

segments.

Kadaba et al., (1990) developed a systematic method for lower extremity external marker
placement, sometimes called the Helen Hayes method, named after the hospital where the
technique was developed. The relatively small number of body surface markers used in
the system render it easy to implement in routine clinical gait evaluations to compute the
motion at the pelvis, hip, knee, and ankle joints. The markers are used to deﬁne a
coordinate system for each segment, and axes and planes about which the limb rotations

take place.

The author has not encountered any study of TMJ motion, human or animal, that utilizes

body surface markers to track the motion.

The location of one coordinate system relative to another is commonly described by Euler

angles (or Cardan angles) or by the concept of a helical axis. Euler angles are deﬁned as

20

a set of three ﬁnite rotations assumed to take place in sequence to achieve the ﬁnal
orientation from a reference orientation (Kadaba, 1990). The displacement of a segment
from one position to another can also be represented as a rotation about and a translation
along a particular axis in space called the helical axis or screw axis (Woltring et al.,
1985). The motion of the mandible relative to the skull will be deﬁned in this thesis by
three successive rotations: pitch, roll, and yaw (Ostry et al. 1997, Fredrickson and
Drevemo, 1971). This research study used a highly accurate optical motion capture
system to track markers attached to the skin overlying bony landmarks on the skull and
mandible of horses during chewing. The data describe the three-dimensional motion of
the equine TMJ by six degrees of freedom: three translations and three rotations, using

Euler angles as the rotational position coordinates.
1.7 Motion Analysis System:

The three-dimensional Optical Motion Capture System from Motion Analysis
Corporation is a high performance video/computer-based instrumentation system that
tests and measures the movement of objects. This system is commonly utilized for
animation production, industrial measurement and control systems, and movement
analysis such as gait analysis, sports medicine and performance, product design and

development, orthotics and prosthetics, and virtual surgeries.

The Motion Analysis system functions like other videographic systems. Spherical retro-

reﬂective skin markers are placed on the segments of interest (assumed to be rigid bodies)

21

and each marker must be seen by at least two cameras. The action to be measured must
take place in a calibrated volume. The coordinates of the skin markers are determined
through automatic digitization, where the marker periphery is located through edge
detection and the center of the marker is calculated. In the McPhail Equine Performance
Center, the Motion Analysis system is typically used for locomotion analysis in horses,
but the highly sensitive system with sub-millimeter accuracy can detect and track much
smaller motions. This project applies the Motion Analysis system to study the kinematics
of TMJ motion during chewing in horses to provide baseline information of
characteristic, normal chewing patterns that can be compared to future studies of

pathological equine TMJ motion.

1.8 Research Objectives:

The goal of this study is to investigate how horses chew different types of food. The
objectives are to describe the normal three-dimensional motion of the equine
temporomandibular joint (TMJ) during chewing and to measure differences in the motion
while chewing hay versus pellets. The null hypothesis is that there is not a signiﬁcant
difference between the mean values of the variables that measure mandibular motion in
horses chewing hay versus pellets. The experimental hypothesis is that the variables

investigated are signiﬁcantly different while chewing hay versus pellets.

22

2. Materials and Methods:

In this section, the subjects and equipment and their preparation will be described. The
data collection procedure and the processing techniques will be discussed next and the

data processing protocol will be explained.

2.1 Subjects:

The subjects were seven horses including one Hanoverian, one Quarter Horse, two
Thoroughbreds, one Morgan, and two Appaloosas. A veterinary dentist veriﬁed that no
malocclusions existed in these horses. The horses ranged from 4-15 years old, 480-655

kg, and 155 to 175 cm tall at the withers (Table 1).

Table 1: Description of horses used in the study

Horse No. Breed
1

Hanoverian

Quarter Horse

 

2.2 Equine Preparation:

Hair was removed with clippers where markers were to be secured, including the
forehead, nose, and right and left angle of the mandible, facial crest, articular tubercle,

and condylar process. The skin was cleaned with rubbing alcohol to remove dirt and

23

sweat. Twelve tracking markers were glued onto the skin with cyanoacrylate glue (super
glue) on the most rigid locations on the skull and mandible (Figure 9). These tracking
markers were placed on the forehead (8) and nose (9) on the midline of the face,
bilaterally on the middle (6) and rostral (7) part of the facial crest, the notch on the
mandible for facial vessels (5) and dorsally (3) and ventrally (4) on the caudal aspect of
the mandibular ramus. In addition, virtual markers were placed on the right and left
articular tubercles of the skull (1) and condylar processes of the mandible (2) on each
side. Due to the close proximity of the tubercles and the condylar processes, two standing
ﬁles were recorded: one with the tracking markers and the articular tubercle virtual

markers and a second standing ﬁle with the tracking markers and the condylar process

virtual markers.

 

Figure 9: Locations of skin markers

24

2.3 Equipment Set-Up:

A Motion Analysis system for kinematic analysis (Motion Analysis Corporation, Santa

Rosa, CA) was utilized for collecting data. Six Falcon infrared cameras (Motion Analysis

Corporation, Santa Rosa, CA) were placed in a semi-circle around of the volume

occupied by the horse’s head (Figure 10).

Camera 3: . .
height = 150 cm
x-distance = 260 cm
y-distance = -270 cm

Camera 2: —>
height = 50 cm
x-distance = 240 cm
y-distance = -70 cm

 

 

 

 

 

T

Camera 1:
height = 240 cm
x-distance = 270 cm
y-distance = -60 cm

Front of horse

1

 

 

l A

 

 

T

Calibrated Volume

Figure 10: Camera set-up

. 4— Camera 4:
height = 150 cm
x-distance = —260 cm
y-distance = -270 cm

' Camera 5:
height = 50 cm
x-distance = -240 cm
y-distance = -70 cm

 

 

 

 

 

f

Camera 6:
height = 240 cm
x-distance = -270 cm
y-distance = -60 cm

The aperture and focus were adjusted for each camera to establish the highest quality

image. The volume was calibrated according to Motion Analysis speciﬁcations. In

addition, a video camera was set up to record the data collection process. A time code

25

super imposed on the video image coincided with the time code ﬁle generated by the

Motion Analysis system.

2.4 Data Collection Procedure:

2.4.1 Standing Files:

The horse stood with its head in the calibrated volume with the tracking markers and the
virtual articular tubercle markers in place. Data were collected for one second at 60 Hz
while the horse was not chewing. A single frame of data is sufﬁcient for a standing ﬁle,
however. The articular tubercle markers were removed and the condylar process markers
were glued in place. Again, the horse stood in the calibrated volume while data were
collected for one second at 60 Hz. The standing ﬁles were later utilized to calculate the
locations of the articular tubercles and condylar processes from the measured locations of

the tracking markers.

2.4.2 Tracking Files:

The virtual markers were removed and the horse was fed hay and pellets in random order
while the head was in the calibrated volume. The hay was a mature, ﬁrst cutting from a
ﬁeld composed of 90% timothy, 10% alfalfa. The pellets and were a commercial
concentrated feed commonly fed to horses on a daily basis. The following table provides

information on the feed samples:

26

Table 2: Description of feed types.

 

Feed Type Description Dry Matter Protein Fiber
Grass Ha Over-mat_ure first cutting 84.40% 8.70% 44.60%
Pellets Purina H_o_rse Chow #100 90.00% 10.00% 30.00%

 

 

 

 

 

 

 

 

 

 

Data were collected at 120 Hz while the horse was chewing the sample (Figure 11) and a
data set was considered acceptable if the horse did not move its head out of the calibrated
volume, did not make any rapid movements with its head, and was not in the process of
ingesting feed. Upon giving the horse the second feed sample, the horse was allowed to
consume the new feed type for at least 2 minutes to ensure that the prior feed type was no
longer in the mouth before collecting data with the new feed type. A minimum of 4

chewing cycles per trial and a minimum of 6 trials per feed type were recorded.

 

Figure 11: Horse standing in calibrated volume, chewing pellet sample

2.5 Data Processing

The x, y, 2 locations of each marker were acquired every 1/120 second during the data
collection. The ﬁles were analyzed through a customized MATLAB (The Mathworks,
Natick, MA) program in order to determine how the mandible moves relative to the skull.

The procedure was as follows:

1) Temporary coordinate systems were created on both the skull and mandible. The
skull’s origin was the forehead marker and the mandible’s origin was the more ventral
marker on the right side of the mandibular ramus. These locations were chosen because
they appeared to have the least amount of skin displacement relative to the underlying
bones during chewing. Skin displacement considerations will be discussed in more detail

in section 4.1.

2) Vectors from the local origin to each marker on the segment were determined.

3) A generalized cross validation was performed on the tracked data in order to remove

high frequency noise in the data (Woltring, 1986). This technique is a ﬁltering process

that ﬁts a cubic spline to the raw data.

4) A transformation matrix and a translation vector were determined using a singular

value decomposition method based on Soederkvist and Wedin (1993).

28

The algorithm by Soederkvist and Wedin (1993) produces a rotation matrix and a
translation vector that describe the rotation and translation of the mandibular coordinate
system from its neutral position (horse not chewing, obtained from the standing ﬁle) to
the new orientation at each frame of tracked data. The algorithm determines the motion
of a rigid body by using the positions of landmarks in a least-squared sense. The method
uses the singular value decomposition of a matrix derived from the positions of the
landmarks. Although the skull and mandible are rigid structures, skin displacement
relative to the underlying bones occurs; this algorithm was employed because it obtains
transformation matrices that minimize high frequency errors that possibly arise from skin
displacement and provides a best approximation of the rotation. Matrix transformations

will be described in full detail in the next section.

5) Upon smoothing the data and obtaining the transformations to describe the motion of
the mandible, an orthogonal coordinate system, based on the skull and mandible anatomy,
was established for both the skull and mandible (Figure 12). This was done in order to

describe the relative motion of the mandible in anatomical terms.

29

 

Figure 12: Location of skull and mandible coordinate systems

The techniques used to create these coordinate systems will be discussed in section 2.7.2.

6) Euler angles were directly calculated utilizing techniques from Ramakrishnan and

Kadaba (1991). Euler angles will be described in section 2.7.3.

7) A virtual midline-mandible marker was created and tracked relative to the skull’s
coordinate system. This marker aids in visualizing the mandibular motion and allows
comparisons to be made to previous studies. The technique used will be explained in

section 2.5 .4.

2.5.1 Coordinate Transformations

A rotation transformation matrix and a translation vector are necessary in order to

describe the 3-dimensional motion of an object in space. A geometric vector is uniquely

30

represented by an algebraic vector that contains components of the geometric vector in a
Cartesian reference frame. The components of a vector, however, are deﬁned in a
speciﬁc Cartesian reference frame. Consider a second Cartesian x’-y’-z’ frame with the
same origin as the X—Y—Z frame, as shown in Figure 13. Unit x’, y’, and z’ coordinate
vectors are denoted by f, g, and h, respectively and unit X, Y, and Z coordinate vectors

are denoted by i, j, and k.

 

 

Figure 13: Two Cartesian reference frames with the same origin
and rotated with respect to each other

A vector s in space can be represented in the X-Y-Z frame as

s=sxi+syj+szk (1)
or in the x’-y’-z’ frame as

s=sx’f+sy’g+sz’h (2)

where

31

sx=50i sy=30j sz=30k (3)
and
sx’=SOf sy’=s-g sz’=30h (4)
The algebraic vectors that deﬁne s and s’ are
s = [s,,,sy,sz]T (5)
in the X-Y-Z frame and
s’ = [s,,’,s,,’,sz’]T (6)
in the x’-y’-z’ frame.
It is clear that there is a relation between s and 3’, since they are deﬁned by the same
geometric vector s. To establish the relationship between s and s’, the f, g, and h unit
vectors are expanded in the terms of the i, j, and k unit vectors as
f: 311i + 321I+ a3|k
g = 312i + 322] +332" (7)
h = 313i +823] + 333k
where aij are the following direction cosines:
an =i0f=cose(i,f)
an = i o g = cos 0(i,g)
an = i 0h: cos 0(i,h)
a21=j0f=cos 0(j,f)
azz =j I g = cos 0 (j,g) (8)
a23=j0h=c030(j,h)

a3i=k0f=cose(k,f)

32

a32=k’829039(k,3)
a33=k0h=cose(k,h)
Substituting Eq. 7 into Eq. 2 yields
3 = (31 in’ + aizsy’ + 31352,)i+(3215x, + Szzsy’ + 32385)] + (331811, + arzsy’ + 213382,)k (9)
Equating corresponding right sides of this representation of s and Eq. (1),
Sx = aier’ + aizsy’ + 31382,
5y = agisx’ + szzsy’ + a23sz’ (10)
S2 = a3lsx’ + a3zsy’ + a33sz’
In matrix form, this is
s = As’ (11)

where A is called the direction cosine matrix or rotation transformation matrix:

all an an
A: a21 “22 “23
“31 “32 “33

(12)

When the origins of the X-Y-Z and x’-y’-z’ ﬂarrres do not coincide, the foregoing

analysis is applied between the x’-y’-z’ and the translated X-Y-Z ﬂame, as shown in

Figure 14.

33

Z 2 Point P

 
 

—>

 

 

Figure 14: Translation and rotation of a reference ﬂame.

If the algebraic vector s’P locates point P in the x’-y’-x’ ﬂame, then in the translated X-Y-
Z ﬂame, the vector is As’P. Thus,

r" = r + As’P (13)
where r is the translation vector ﬂom the origin of the X-Y-Z reference ﬂame to the
origin of the x’-y’-z’ ﬂame.

In the present study, the transformation matrix and translation vector are obtained in order
to describe the orientation of the mandible ﬂom its neutral (non-chewing) position to the

position at each ﬂame.

34

2.5.2 Coordinate System Development

The skull and mandible are treated as rigid bodies and in order to describe how one
moves relative to the other, each needs its own orthogonal coordinate system. The skull
and mandible unit vectors are analogous to the i, j, k and f, g, h unit vectors respectively

in Figure 13.

The tubercle markers were used to establish the y-axis of the skull’s coordinate system:

tubercle left - tubercle right
I tubercle leﬂ — tubercle rightl

skull '—

 

(14)
This establishes a unit vector ﬂom the right tubercle to the left tubercle.
Two unit vectors were established along the facial crests, ﬂom the mid-facial crest
markers to the rostral marker on each side. A temporary I’-axis of the skull was

established by averaging the right and left unit vectors:

__ right vector + left vector

 

I'skull _ 2
(15)
The 2 and x-axes was determined by utilizing principles of cross products:
K skull : 1.5/cull XJ skull
(16)
I skull : Jskull X K skull
(17)

35

The origin of the skull was the midpoint between the tubercle markers:

tubercle left + tubercle right

Skull Origin 2 2

 

(18)
A similar technique was applied to the mandible where the j-axis was established using

the condyle markers:

_ condyle left -c0ndyle right

 

 

Jmandible — .
I condyle left - condyle right I
(19)
The 1’ axis established for the skull was also used for the mandible:
I 'maudible = I'm”
(20)
The z and x-axes was determined by utilizing principals of cross products:
Kmaudible : I ’mandible XJmandible
(21)
[mandible = Jmandible X K mandible
(22)
The origin of the mandible was the midpoint between the condyle markers:
Mandible Origin : condyle left +2c0ndyle right
(23)

The motion of the mandible coordinate system relative to the skull coordinate system was

described using Euler angles.

36

2.5.3 Euler Angles

Euler angles are the three successive rotation angles that describe a body’s orientation in
three-dimensional space. In 1776, the Swiss mathematician Euler ﬁrst established a
series of transformations to describe the motion of a spinning top. Euler angles are
sequence dependent, that is, the rotations must occur in a speciﬁc order to properly
describe a body’s orientation. These rotations are typically labeled 0:, B, and y and in gait

analysis, the rotations have the following deﬁnitions and anatomical descriptions:

Step 1: Rotation 0t (ﬂexion/extension) about the Y-axis

 

Y, Y,

 

37

Step 2: Rotation B (ab/adduction) about the Xl—axis (also called the ﬂoating axis)

 

22’ Z3

 

38

The terminology used in gait analysis is not applicable in describing the motion of the
TMJ. Gait analysis terminology describes joint motion of limbs and how they move
relative to the midline of the body. In this case, the skull and mandible are on the midline
of the body and more appropriate terminology must be used. In a study performed by
Ostry et al. (1997), the three rotations of the human mandible have been described as
pitch, roll, and yaw where pitch is a rotation at about the Y (transverse horizontal) axis,
roll is a rotation [3 about the X1 (longitudinal) axis, and yaw is a rotation 7 about the 22
(vertical) axis (Figure 15). Fredricson and Dreverno (1971) also used this terminology to
describe the equine hoof motion during racing. This is the convention utilized in this

study.

  
   

a, PITCH

I +

 

 

 

 

 

Figure 15: Description of mandibular rotations

39

Utilizing the convention of right-handed coordinate systems, a positive pitch (rotation or
about the y-axis) is deﬁned as opening the jaw and negative pitch is closing the jaw. This
is contrary to Ostry’s deﬁnition, where negative pitch is opening. A positive roll is a
counter-clockwise rotation B about the x-axis when viewed ﬂom the ﬂont of the horse
and a negative roll is a clockwise rotation. A positive yaw occurs when the jaw rotates
(y) clockwise about the z-axis when viewed ﬂom above the horse and negative yaw is

counter-clockwise.

The rotation matrix, R, is established through the following equation:

R = Z(Y)X(B)Y(0t) (24)

Setting Eqn. (12) = Eqn.(24), the rotational angles can be calculated:

Roll = B = arcsin(-K mandible o J skull) (25)
Pitch = or = arcsin(K mandible o I skull/cos(B)) (26)
Yaw = y = arcsin(l mandible 0 J skull/cos(B) (27)

2.5.4 Midline-Mandibular Marker Development:

In order to measure the displacement of the mandible, a tracking marker placed on the
midline of the mandible would have been ideal. The only bony structure on the midline is
at the mandibular symphysis, just caudal to the lower lip. This location, which is in close
proximity to the lips, is not suitable for a marker due to the high amount of skin

displacement occurs at that location while chewing. Therefore, a virtual marker was

40

created along the midline of the mandible utilizing the average x-coordinates of the
rostral facial crest markers (marker #7 in Figure 16) and the z-coordinates of the markers
placed on the notch (marker #5 in Figure 16) on the mandible ﬂom the standing ﬁle. The
y-coordinate was set equal to zero to place this virtual marker on the midline of the

mandible.

Virtual Midline
Mandible Marker

 

Figure 16: Location of Midline Mandibular Marker

This mandibular marker, originally a static marker represented in mandible coordinates,
was ﬁrst converted into a tracked marker in global coordinates. This was accomplished
by multiplying the markers location by the i-j-k unit vectors of the tracked mandible

coordinate system for each ﬂame of data. The mandible origin was then added to this

41

product in order to represent the midline marker in global coordinates. The marker, now
expressed in global coordinates, was represented in the skull’s coordinate system in order
to observe how the marker moved relative to the skull. This was achieved by creating a
vector ﬂom the skull origin (located half way between the tubercle markers) to the
midline-mandible marker. This vector was then multiplied by the i-j-k unit vectors of the
skull coordinate system to express the midline marker in terms of the skull coordinate

system.

42

2.6 Data Post-Processing

2.6.1 Cycle Definition

Data were processed for three trials per feed type for each horse. Each trail was deﬁned
by three consecutive chewing cycles. The cycles with the least amount of overall head
movement were manually selected for each trial as rapid head movement may cause
undesirable marker movement. A cycle was deﬁned ﬂom one minimum pitch angle to
the next. The minimum pitch angle coincides with the mouth being fully closed. As the
mouth opens, the pitch angle increases to a maximum value when the mouth is fully
opened. The mouth closes again and the pitch angle decreases to a minimum when the
mouth is fully closed. Each cycle had several local minimum and maximum pitch angles,
therefore, the minimum pitch angle with the largest magnitude was manually selected to

deﬁne the starting and ending ﬂames of each cycle.

2.6.2 Data Normalization

All tracked and standing ﬁles were processed with customized software. The output
included the x, y, and 2 location of the midline-mandibular marker relative to the skull’s
coordinate system and the three Euler angles and translations that describe the orientation
of the mandible, relative to the skull, for each ﬂame of data. In order to normalize the
data, the output ﬂom the standing ﬁles was subtracted ﬂom the tracking ﬁle output for all
trials. The x, y, and 2 locations of the midline-mandibular marker and the mandible

relative to the skull were averaged over the 60 ﬂames of standing ﬁle data and subtracted

43

ﬂom the x, y, and 2 values ﬂom the tracked ﬁles. Likewise, the average of each Euler
angle was determined in the standing position and subtracted ﬂom the tracked ﬁles. This
referenced the midline-mandibular marker location, mandible coordinate translation, and
Euler angles to their standing positions. The data are referred to as “normalize ” to

distinguish them ﬂom the raw date in the following sections.

2.6.3 Processing Midline-Mandibular Marker Data

A virtual midline-mandibular marker was created to aid in visualizing mandibular
motion. From the normalized data, the minimum and maximum x, y, and 2 values of the
midline-mandibular marker data were found for every cycle. The total displacement in
the x, y, and 2 directions was calculated by subtracting the minimum ﬂom the maximum
values in each direction. The displacements were calculated for every cycle, averaged for
each trial, and the three trials were averaged for each horse, as stated in section 2.6.1.
The area contained within the path that the midline-mandibular marker described was
calculated in the z-y plane for each cycle and averaged in the same manner as the
displacements. The absolute velocity of the midline-mandibular marker was calculated

and averaged.

2.6.4 Processing Mandibular Coordinate System Data

From the normalized data, the minimum and maximum x, y, and 2 values of mandible

coordinate system data were found for every cycle. The total displacement in the x, y, and

2 directions was calculated by subtracting the minimum ﬂom the maximum values in
each direction. The displacements were calculated for every cycle, averaged for each

trial, and the three trials were averaged for each horse.

2.6.5 Processing Euler Angle Data

The minimum and maximum values were found for each angle and trial ﬂom the
normalized data. The total angular displacement for pitch, roll, and yaw were calculated
by subtracting the minimum values ﬂom the maximum for each cycle and averaged for

each horse.

2.6.6 Statistical Analysis:

Three cycles of data were evaluated for each trial and three trials were evaluated for
each feed type. The variables investigated were averaged over the three cycles for
each trial and the three trials were averaged and standard deviations (SD) determined
for each horse (sample size, n, is three). The mean values of the variables of interest
while chewing hay and pellets were compared for all horses using a two-tailed paired
samples t-test (SPSS, Inc., Chicago, IL). The necessary assumption for applying the
paired t-test is that the data have a normal distribution (Triola, 1998). In this study,
the sample size for the paired t-test computation, N, is 7, for the number of horses, the
standard deviation for the entire population is not known, and the data were plotted

and subjectively appeared to have a normal distribution, therefore the normal

45

distribution assumption is not unreasonable. In this test, the t statistic is calculated
by:

d

: (”‘8 (28)
SD, NW

t

where dave is the mean difference between the average values, for each horse, while
chewing hay versus pellets, SDd is the standard deviation of the differences and N is the
number of pairs (7 in this study). The corresponding signiﬁcance value associated with
“t” can be looked up in a t-distribution table or calculated with software. In this study, 7
horses were examined and therefore there were 6 degrees of ﬂeedom (N-l). A 95%
conﬁdence interval, which is a measure of how certain we are that the interval contains
the population parameter, (Triola, 1998) was chosen. The choice of 95% is most common
because it provides a good balance between precision and reliability (Triola, 1998).
Values were considered signiﬁcantly different when the conﬁdence parameter, p, was
less than 0.05. This signiﬁcance level indicates that less than 5% of all the tests for
signiﬁcant differences between hay and pellets will be false positive. This level of
signiﬁcance is standard in most studies evaluating biological data. A signiﬁcant
difference in values will reject the null hypothesis, that there is not a signiﬁcant
difference between the mean values of the variables that measure mandibular motion in

horses chewing hay versus pellets.

46

3. Results:

In this chapter, results for the midline mandibular marker, including its motion in all three
planes for a horse chewing on the right and left and the differences between chewing hay
versus pellets are displayed ﬁrst. The mean area the marker encompasses, and the mean
velocity and cycle duration will follow. Finally, the mean x, y, z and angular
displacements for the mandibular coordinate system are provided. The ﬁgures

illustrating these results are at the end of the chapter.

3.1 General Midline-Mandibular Marker Motionz.

When a horse chews, occlusal contact only occurs between the cheek teeth of the side
being chewed on. Therefore, in a chewing cycle, the horse chews on either the left or the

right side. During this study, four horses were chewing on the right and three on the left.

The data were plotted in the z-y plane (observing the motion ﬂom the ﬂont of the horse),
the z-x plane (observing ﬂom the right of the horse), and the x-y plane (observing ﬂom
above the horse). These orientations are depicted in Figure 16. The z-y plane is the

transverse plane, the z-x plane is the sagittal plane, and the x-y plane is the dorsal plane.

The location of the midline-mandibular marker relative to the skull’s coordinate system
was plotted in all three planes. When the movements of the midline-mandibular marker
in the z-y plane are viewed ﬂom the ﬂont in a horse chewing on the right side (Figure
17), the lower jaw starts in the upper-most, closed position (1), then moves clockwise and

slightly to the horse’s left (i.e. to the right of the graph) to its maximum pitch angle (2).

47

As the jaw starts to close, it swings to the horse’s right (moving to the left of the ﬁgure)
to the position of maximum lateral excursion for the cycle (3). At this point, the cheek
teeth establish contact to grind the food as the jaw slides to the left and upward to return
to the starting position (1). Chewing in this direction is considered chewing on the right

side because the cheek teeth on the right side of the jaws are utilized for grinding.

A horse chewing on the left starts with the lower jaw in the closed position (1), followed
by the jaw moving counter-clockwise, when viewing ﬂom the ﬂont of the horse, as it
opens and moves slightly right to its most open position (2). The jaw then swings to its
left-most position as it closes (3) and the left cheek teeth establish contact to grind

(Figure 18).

The path that the midline-mandibular marker follows has the same basic geometry while
chewing hay and pellets. There is a difference, however, in the mandibular excursion of
the cycles for the two feed types. Comparison of the mandibular movements in the z-y
plane when chewing hay versus pellets shows that the mandible undergoes more lateral

excursion while chewing hay compared to pellets (Figure 19).

When observing the z-x plane of a horse chewing on the left (Figure 20), the midline-
mandible marker moves in the negative x and z-directions while the lower jaw opens and
positive x and z-directions as the jaw closes. In the x-y plane of a horse chewing on the
left (Figure 21) this marker moves in the negative x and y—direction during the opening

phase. During the closing phase, the maker initially moves in the positive y-direction,

48

then moves in the negative y-direction. The marker moves in the positive x-direction for

the duration of the closing phase.

In general, the midline-mandibular marker moved in the negative x- and z-directions
(caudoventrally) during the opening phase of the cycle, and in the positive x- and 2-
directions (rostrodorsally) during closing. The motion in the y-direction depended on if

the horse was chewing on the left or right.

Graphs of the location of the midline-mandibular marker for all three planes for all

chewing cycles for each horse and feed-type can be found in Appendix A.

Chewing cycles are complicated with many detailed features. To quantify the cycles,
mean and standard deviations for x, y, and z displacements, velocities, and areas
encompasses by the path of the midline-mandibular markers were calculated and
tabulated for all horses while chewing both hay and pellets. The mean values for each
variable were compared while chewing hay versus pellets with a paired t-test as described
in section 2.6.6. For example, in comparing the statistical difference between the
mandibular marker x-displacement while chewing hay versus pellets (Table 3), the
difference (1 between the mean x-displacement value for hay and pellets was determined
for each horse. The mean value and the standard deviation (SDd) of the difference d
across the seven horses were used to compute the variable t for the paired t-test (eqn. 28).
The bottom row in the tables represents the means across the values entered in the table

for the seven horses, and the standard deviations of those numbers. These numbers do

49

not account for the standard deviations in each line of the table and are not used to verify

the hypothesis through the paired t-test.

The displacements of the midline-mandibular marker in the x, y, and z-directions were

determined for each cycle and averaged (Table 3). Based on the paired t-test, the

displacements in the x, y, and 2 directions for the entire group were signiﬁcantly larger

for hay than for pellets, under the assumption that the data have a normal distribution.

Consequently, the null hypothesis will be rejected and the experimental hypothesis

accepted. Horse #4 varied ﬂom the group, however, this did not effect the statistical

result.

Table 3: Mean (SD) x, y, and z displacement of the midline-mandibular marker for each
horse while chewing hay and pellets

 

Mean X-Disp. (SD) (mm)

Mean Y-Disp. (SD) (mm)

Mean Z-Disp. (SD) (mm)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Horse HAY PELLETS HAY PELLETS HAY PELLETS
1 5.86 (0.56) 3.47 (0.12) 13.33 (1.39) 11.03 (0.22) 13.33 (1.34) 12.05 (0.14)
2 6.76 (2.64) 5.02 (0.60) 23.51 (0.79) 17.91 (0.74) 19.25 (1.24) 17.97 (0.75)
3 7.14(1.27) 4.71 (0.10) 17.35 (0.73) 12.16(0.36) 16.44 (0.30) 11.33 (0.23)
4 4.40 (1.06) 4.97 (0.57) 21.74 (0.75) 15.90 (1.96) 11.63 (0.86) 11.33 (1.30)
5 5.34 (1.14) 4.02 (0.54) 16.95 (0.67) 13.53 (0.67) 21.00 (0.26) 18.19(O.62)
6 7.20 (3.16) 5.58 (0.79) 19.01 (1.37) 17.31 (1.69) 13.67 (0.33) 12.29 (0.72)
7 5.37 (0.41) 4.30 (0.39) 21.73 (2.61) 19.75 (1.72) 15.03 (0.29) 13.23 (0.23)
Total Mean 3.03 (1.02) 4.53 (0.71) 19.37 (2.43) 15.33 (3.22) 15.77 (3.36) 13.93 (2.37)

 

The area encompassed by the midline-mandibular marker in each cycle, was calculated

for the z-y plane and averaged in a similar manner (Table 4). The area encompassed

when chewing hay was signiﬁcantly larger than when chewing pellets, rejecting the null

hypothesis.

50

 

Table 4: Mean area encompassed by each cycle in the z-y plane for hay and pellets

 

 

 

 

 

 

 

 

 

 

 

 

 

Mean Area SD) (mm2) _
Horse HAY PELLETS
1 146.27 (6.95) 94.43 (3.49)
2 306.95 (29.52) 240.75 (5.31)
3 190.77 (3.31) 93.72 (5.53)
4 168.82 (17.29) 119.03 (24.51)
5 237.56 (20.63) 147.60 (14.90)
6 137.29 (10.26) 112.13 (9.24)
7 154.23 (6.26) 100.53 (2.31)
Total Moan 191.71 (61.71) 129.75 (52.33)

 

 

The absolute velocity of the midline-mandibular marker was determined for each cycle
and averaged for each horse (Table 5). The mean velocities for the hay and pellets were

very similar, failing to reject the null hypothesis for this variable only.

Table 5: Mean absolute velocity for all horses for each feed sample.

Meanv
Horse Y
.10 1
87.15 . 115.79 11.1
75.07 .61 65.81 4.1

81.03 5.1 77.85
77.44 3 71.87
70.56 72.89 4.
85.05 92.51
Total Mean 77.63 79.03

 

The cycle duration was determined for each cycle and averaged for each horse and the
mean ﬂequency was calculated for hay and pellets (Table 6). The mean duration for hay

was signiﬁcantly longer than for pellets, rejecting the null hypothesis.

51

Table 6: Mean cycle duration for all horses for each feed sample

Mean Duration
Horse HAY
.04 26 .
1007.41 601.85

906.48 1 698.15 .4

722.22 681.48
847.22 12.11 744.44 1

883.33 . 717.59
725.00 65. 624.07 11

Total Mean 846.96 1 677.65
Mean 1.18 1.48

 

3.2 Mandible Coordinate System Displacement:

The location of the origin of the mandible coordinate system was plotted relative to the
origin of the skull coordinate system in all three planes. In general, during the opening
phase, the mandible tended to move in the positive x- and negative z-directions
(rostroventrally) and in the negative x and positive z- directions (caudoventrally) during
the closing phase. The motion in the y-direction was highly variable throughout the

chewing cycle (Figures 22-24).

The three planes for additional sample chewing cycles for each feed-type can be found in

Appendix B.

The displacements of the mandible coordinate relative to the skull coordinate system in
the x, y, and z-directions were determined for each cycle (Table 7). The mean
displacements in the x, y, and 2 directions were signiﬁcantly larger for hay than for

pellets, rejecting the null hypothesis.

52

Table 7: Mean (SD) x, y, and z displacement of the mandible coordinate system relative
to the skull coordinate system for each horse while chewing hay and pellets

X Z
HAY Y
1. 1 1. 7. . . .
19.45 . 13.03 4.43 0
18.24 1. 12.42 0. 5.64 O.

6.99 1.01 6.85 0 3.12 0.51
23.24 1. 18.84 4.87
12.36 1 13.72 0. 4.64 1.
12.90 1.94 9.58 1 5.19
Total Mean 14.88 11.75 4.1 4.37

 

3.3 Euler Angles:

The three Euler angles were plotted for all trials. The beginning and end of each cycle
were deﬁned ﬂom the pitch angles. The beginning of the ﬁrst cycle was deﬁned by the
ﬁrst minimum value in the trial, which corresponds with the jaw in its fully closed
position. The lower jaw opens (positive pitch) until a maximum is reached, which
corresponds with the fully open position. The jaw then begins to close (negative slope)
until the next minimum value is reached where the mouth is closed again and the ﬁrst
cycle is complete. The pattern was repeated twice to deﬁne cycles 2 and 3. The cycles
were deﬁned for each trial and all angles were plotted within the deﬁned ranges (Figure

25).

Euler angles for all horses can be found in Appendix C.

53

The maximum and minimum angles were averaged for each trial and the angular
displacements were determined for each horse (Table 8). The mean range of motion for
pitch, roll, and yaw were signiﬁcantly larger for hay than for pellets, rejecting the null

hypothesis.

Table 8: Mean range of Euler angles for all horses chewing hay and pellets

Pitch Roll Yaw
Horse HA
. 1 . 1 4
5.47 2.37 0.41 3.70 0.
4.94 . 1.81 0.1 4.44 0.1

2.51 . 1.16 .1 4.35

7.17 . 1.81 .1 . 4.47 0.1

4.42 . 1.54 . 3.67 0.1

4.07 1.44 0. 2.94
Total Mean 4.50 1.56 . 3.91

 

54

 

 

N‘

Figure 17: The three planes the data are described in

55

 

       
   
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

l T l l l I r
2 _ m-I Opening Phase
‘ — Closing Phase
I"
1 2
‘3
0 - a _
i
i
i
i
i
-2 >— 9 —
A
E
E I.
v I
m '2
.. . _
i5 “‘ * .—,
0
N a,
Q,
‘,
2
-6 -— 2 _
l
5,
E
I
i.
- I s
8 r i
!
9
.0
L 3 r
-6 -4 0 2 4 6 8

Y-axis (mm)

Figure 18: Normalized midline-mandibular marker location in the z-y plane from one
chewing cycle viewed ﬁ'om the front of a horse #1 chewing hay on the right.
Number 1 = lower jaw in closed position, number 2 = maximum pitch angle, number 3 =
maximum lateral excursion. Arrows indicate the direction the mandible moves.

56

 

 

 

I l l l
.rﬂtﬂtﬂt."-J I'I' Opening Phase
\1 — Closung Phase

 

 

 

 

 

 

 

 

 

I
N

Z-axis (mm)

I
m

 

 

 

 

 

 

 

 

 

Y-axis (mm)

Figure 19: Normalized midline-mandibular marker location from one chewing cycle
viewed in the z-y plane of a horse #4 chewing hay on the left
Number 1 = lower jaw in closed position, number 2 = maximum pitch angle, number 3 =
maximum lateral excursion. Arrows indicate the direction the mandible moves.

57

Z-axis (mm)

 

 

 

 

r
IIII Opening Phase
— Closing Phase

 

 

 

.\"
l

 

 

 

3, -
‘I
e
g
g _
g
g
g
E .—
g
g
g
E _
,5
\.\.\ _
9
1 l J I. r 1
-15 -10 -5 0 5 10

Y-axis (mm)

Figure 20: Normalized midline-mandibular marker viewed in the
z-y plane from one chewing cycle of hay (thicker line) and
pellets (thinner line) from horse #5 chewing on the right.
Arrows indicate the direction the mandible moves.

58

N

 

J

 

 

 

 

 

T
mm Opening Phase
2 — Closing Phase
r—

0 — a
A-Z _ _.
E
E
v
.E”.

a .4 i— .—
N
.5 .. z
-8 _ _
l l

 

 

 

 

15

X-axis (mm)

Figure 21: Characteristic chewing patters of the normalized
midline-mandibular marker location from one chewing cycle of
horse #4 chewing hay on the left, viewed in the z-x plane.
Arrows indicate the direction the mandible moves.

59

X-axis (mm)

 

N‘

 

 

 

I I
.1... Opening Phase
— Closing Phase

 

 

 

 

 

 

l L l

 

18 20

6 8 1o 12 14 16
Y-axis (mm)

Figure 22: Characteristic chewing patters of the normalized
midline-mandibular marker location from one chewing cycle of
horse #4 chewing hay on the leﬁ, viewed in the x-y plane.
Arrows indicate the direction the mandible moves.

6O

Z-axis (mm)

 

 

 

I
mm Opening Phase
'1-5 ” — Closing Phase “

 

 

 

.2r _

-2.5 r

1
U
l

5'»
01
l

L
l

 

\.
‘4.5 kmg’.l.' ‘.

I.‘\ ‘.’.J.,.
I-|-|.'-l-|.|-|-I-n—

 

 

 

12 13 14 15 16 17
Y-axis (mm)

Figure 23: Location of mandible coordinate system during one sample
chewing cycle from horse #4 chewing hay on the left viewed in the z-y plane.
Arrows indicate the direction the mandible moves.

61

Z-axis (mm)

 

PX

 

 

 

 

 

 

 

 

 

 

-1.5 r- _
-2 — _.
.‘.l.lIlIlIlIl-i.,. ‘.'.l*'.l.l.
”2.5 '— .\‘\" I.’.!.’.l.|-|'\' ’~l.’ _
a" ‘.
3
‘1." _
.0‘
Q
!
! I-1
!
!
5
! —1
l
.l-l-j.,
.\‘\ .1
“.10 I.’QIQII
-5 _ _
-5.5 — _
-5 - 4
1 l l 4 l l l
3 4 5 6 7 8 9
X-axis (mm)

Figure 24: Location of mandible coordinate system during one sample
chewing cycle from horse #4 chewing hay on the left viewed in the z-x plane.
Arrows indicate the direction the mandible moves.

62

 

 

 

 

 

 

 

  
     

 

 

 

\
X
T T T "\ I I
9 "' \.1.\""r -'.' ope'im Phase ,__
.o" — Closing Phase
O".
o‘“
\ :’~’
8 " e. i _.
’s, s ,
’\
“ \“’\‘\.‘*
7 _ ‘i.,.,‘\. i _
.9
A \“
E o“
.5
5,6 9‘
.2 a,
5 1
I O
x a
5 e R _
9
‘I
S
Q
.5
4 _ g -
'I
‘QI
3 — _
1 l r r r r r r r
1 1 12 1 3 14 15 16 17 18 19
Y-axis (mm)

Figure 25: Location of mandible coordinate system during one sample
chewing cycle ﬁom horse #4 chewing hay on the left viewed in the x-y plane.
Arrows indicate the direction the mandible moves.

63

 

 

 

 

 

 

 

 

 

A
4 l 1 l l T I I
g 0‘ III1 Opening Phase
v 5 . — Closing Phase
0 2 ’- i 0" 's
a \' \.\ Os
9 3 .
E 0 >— .\.l.‘. ,..O ‘\' —1
.C 1“
o
E _2 1 4 1 1 1 1 1
20 40 60 80 100 120 140 160 180
3

 

 

g... Opening Phase
.1». — Closing Phase

.9""’“‘~
O

 

 

- o
I‘ ’.1"-‘-,.

I

 

 

Roll Angle (Deg)
N 3’.
a
‘0‘
0'
i

 

 

 

 

 

 

 

 

1 5 l l l l l l 1
20 40 60 80 100 120 140 160 180
A-1
l \ l r y l I \ K I
§ “T“ om p...
V-Z ~ 'I‘ ‘0 — Closmg Phase P
2
01-3 ~ -
c
g -4 ’- d
>_ _5 1 1 1 1 1 1 I 1
20 40 60 80 100 120 140 160 180

Frame Number

Figure 26: Euler angles for one trial from horse #1 chewing hay on the right:
pitch (top), roll (middle), and yaw (below)

64

4. Discussion:

In the realm of equine medicine, dentistry has received relatively little attention
compared with other areas, such as infectious diseases. This is at least partly due to the
lack of an accurate method for studying chewing movements and the development of
dental wear patterns. This study described a method of measuring the kinematics of
chewing and has demonstrated the value of the technique in characterizing the kinematic

differences between chewing two types of food.

4.1 Signiﬁcance of Marker Placement:

The principle of virtually all modern kinematic analysis techniques is the marking of the
skin overlying certain anatomically deﬁned landmarks, with subsequent recording of the
trajectories of these markers (van Weeren, 1989). This was the technique applied in
evaluating the kinematics of the mandible during chewing. The use of skin markers in
kinematic analysis introduces an uncontrollable source of biological error since
movements of the skin are recorded and not those of the underlying skeletal structures,
which are the real subjects of study. There always exists a certain degree of sliding of the
skin over the underlying bone, the amplitude and direction of which can be expected to
vary per site. As the skin displacement is cyclic with the same frequency as the skeletal

cycle, it cannot be detected in the raw data (Capozzo et. al, 1988).

65

Because skin displacement is a systematic error, it is important to either adhere skin
markers to regions with minimal soft tissue motion or correct for skin displacement.
Often, in studies that have received a lot of attention, such as human knee and ankle
kinematics, algorithms have been developed to account for skin displacement.
Algorithms can be generated by inserting a pin into the bone under the skin being
evaluated and comparing the relative displacement of a skin marker with the bone pin on
the segment while the motion being evaluated is taking place. Reinschmidt et al. (1997)
for example, examined human knee kinematics and quantiﬁed the difference between
skin and bone marker kinematics using the average root mean square difference and the

maximal difference between the knee rotations.

There have not been any bone pin studies to analyze the skin displacement relative to the
equine skull and mandible during chewing. The actual skin displacement can be
determined by inserting a bone pin into the mandible with the marker set in place. Since
the pin is a rigid structure ﬁxed rigidly to the bone, it provides an accurate representation
of the movement of the bone. Comparisons between the movement of the bone with the
movement of the skin marker allow the amount of skin displacement relative to the bone
to be quantiﬁed and correction algorithms to be developed. Other, less invasive,
techniques such as attaching magnets to the incisors and tracking their motion with a
magnetometer mounted on the skull would also provide pure mandibular kinematics that
can be compared to the motion of the markers (Plesh et al., 1993). This technique would
be suitable as long as the horse’s natural chewing pattern is not inﬂuenced by a magnet

adhered to the incisors. Salomen and Waysenson (1979) tracked the three-dimensional

66

motion of a small radioactive source, cemented into the position of interest. The
radiation emitted by the source is detected by a scintillation detector, which counts the
amount of radiation falling on its surface by transforming the radiation into a proportional
electric current. This technique would provide the pure mandibular motion, however, the
scintillation detector would need to be mounted on the skull in order to determine the

mandibular motion relative to the skull, which may not be feasible.

In the absence of correction algorithms for the equine mandible, the skin markers were
placed in sites where skin displacement was expected to be small based on the fact that
skin was tightly adhered to the underlying bone without the intervention of copious loose
soft tissue. Pilot studies helped determine these locations. Markers were placed on the
rigid portion of the mandible and a software package, provided by Motion Analysis, was
employed to evaluate the relative displacement between the markers. The locations with

the least amount of displacement were chosen in the study.

Previous studies (Baker and Easley, 1999; Collinson, 1994) have attempted to measure
the displacement of the mandible by observing how a point on the midline of the
mandible moved relative to a point on the midline of the skull. Problems with this
technique will be discussed later. In the present study, in order to track the mandibular
motion in a similar manner and make comparisons to Baker and Easley’s and Collinson’s
results, a marker needed to be placed along the midline of the mandible. However, the
only bony structure on the midline of the mandible is at the mandibular symphysis, just

caudal to the lower lip. Unfortunately, this location is not suitable for marker placement

67

due to the high amount of skin displacement that occurs at that location while chewing.
The motion of the lips displaces the skin in that region due to their close proximity.
Therefore, a virtual marker was created along the midline of the mandible using the
average x-coordinates of the rostral facial crest markers and the z-coordinates of the
markers placed on the notch on the mandible from the standing ﬁle. The y—coordinate
was set equal to zero to place this virtual marker on the midline of the mandible. This
virtual marker was then tracked relative to the skull’s coordinate system and the
mandibular motion measured in this manner can be compared to previous studies, such as

Leue’s (1941) and Collinson’s (1994).

The transformation matrix obtained through the algorithm by Soderkvist and Wedin
(1993) more accurately represents the motion of the segment if the marker set is well
conﬁgured. Well-conﬁgured marker placement requires that the markers have a broad
distribution, that they are not placed colinearly. If a segment’s markers are placed in a
straight line and the segment rotates about that line, the motion cannot be detected
because the linear arrangement of markers does not appear to move to the detection
system. Therefore, the more distributed the marker placement, the more accurately the

transformation matrix will represent the actual motion.

The coordinate systems for both the skull and mandible were created from markers
placed on the skin overlying bony, anatomical landmarks. The coordinate systems’
locations are highly sensitive to marker placement, especially those on the articular

tubercles and condyles, which deﬁne the y-axis of the skull and mandibular coordinate

68

systems, respectively. The y-axis was also utilized to deﬁne the z—axis through principles
of cross products. Consequently, the correct marker placement was critical to produce

results that adequately represented the chewing motion.

The relatively small bony prominence at the tubercles and condyles required the use of
markers with a base that had a slightly smaller surface area compared to the markers at all
other locations. A disadvantage to using markers with a small base is that it allowed the
markers to sag away from the landmarks they were placed on under the inﬂuence of
gravity, which shifted the y-axis ventrally by as much as 1 cm. This issue did not affect
the data trends, but it is possible that the origins of the skull and mandibular coordinate

system could have been shifted slightly below the anatomical axes.

In addition, if the glue holding the markers in place was not completely set at the start of
data acquisition, or if the underlying skin was dirty, the markers occasionally fell off and
had to be re-glued in place. Typically, the markers were glued precisely at the location
they fell from because the glue remaining on the skin indicated the location, but it is
possible that minor deviations did occur. The consequence of this shift did not inﬂuence
a given trial, but may have introduced small variations in the results between trials

recorded before and after the marker relocation.

The author has not discovered any human TMJ kinematic investigations that used surface

skin markers, however, magnetic resonance imaging, optoelectronic systems, and

magnetometers have been used. MRI units are not designed to be functional for horses

69

and a magnetometer system requires placing magnets on the incisors, which would likely
disrupt a horse’s natural chewing pattern. Neither system is as accurate as the Motion
Analysis System. Optoelectronic systems ﬁrnction by tracking light-emitting diodes,

which is similar to the Motion Analysis tracking system.

4.2 Diet Effects on Dentition

As horses were domesticated, their natural, grazing diet was modiﬁed by feeding more
concentrated feeds to supplement the reduced roughage intake and provide adequate
nutrition. Not only does this diet change effect the chewing patterns of horses, but it also
requires the gastrointestinal system to process large quantities of concentrate (such as
grain and pellets) rather than roughage consumed continuously throughout the entire day,
as it is designed to do. In addition, horses lack the rurninant’s ability to regurgitate and
remasticate food, and thus are more dependent on a dentition that can effectively break
down forages to release cell contents for nutritional uptake. Given complete freedom on
pastures, horses spend as much as sixteen hours a day nibbling, chewing, swallowing,
and digesting food, little by little to prevent their small stomachs from becoming empty

(Duncan, 1992).

The folded layers of dentin, cement, and enamel that construct the horse’s teeth provide a
self-grinding mechanism that weandown the opposing occlusal surface. When the horse
chews, the jaws separate to the maximum pitch angle followed by the lower jaw moving

laterally as the pitch angle decreases until occlusal contact is again established. The teeth

70

abrade against each other in order to grind food particles, which also wears down the
occlusal surface as the lower jaw moves medially to the neutral position. A horse that
chews with maximal lateral excursion will make complete occlusal contact and will wear
the molar table evenly and adequately. If a horse regularly chews with inadequate lateral
excursion, overgrowths will develop on the buccal side of the upper molar table and on
the lingual side of the lower molar table. Initially, sharp enamel points form, which can
evolve into more serious malocclusions that will further inhibit mandibular lateral

excursion.

Gobel and Duffner (1954, cited by Dixon 2000) noted that overgrowths could be reduced
by a high roughage diet and conversely were encouraged by feeding a high concentrate
diet, such as pellets. Becker (1962, cited by Dixon 2000) also noted that such
overgrowths are rarely found in species that are constantly grazing, such as zebras,
Przewalski’s horses, mules, or African donkeys and are very slight when they do occur.
Brunner (1941, cited by Dixon 2000) found no evidence of enamel overgrowths in fossil
equine skulls. Becker (1942, cited by Dixon 2000) examined 1000 domesticated horses
and found sharp enamel overgrowths in 99.2% and buccal trauma in 78.8%. A later
study of 32,000 cavalry horses showed enamel overgrowths in 91.7% and shear mouth in
0.3% (Becker 1945, cited by Dixon 2000). These ﬁndings indicate that thedental health
of domesticated horses is much worse than that of non-domesticated equids, which
insinuates that an ample, high roughage diet that a non-domesticated horse would eat is

more desirable for improved dental health.

71

Properly maintaining a horse’s overall health, especially for an active performance horse,
should consider the effects of concentrate feeds. Racehorses, for example, have a
considerable workload and must therefore maintain a high calorie diet. Eating
concentrate feeds provides the necessary nutrient density in a smaller volume. A horse
would have to consume an extremely high volume of hay to obtain the calorie
requirements and maintain body weight if concentrates were not given. In addition, the
bulky mass of food that would accumulate within the large intestines on a hay-only diet is
not desirable for hi gh-exertion performance horses. Consequently, the equine manager
must be sure that an equine dentist maintains proper dental occlusion with routine

treatments as chewing large amounts of concentrate feeds can attribute to malocclusions.

Horses chew on one side at a time. In this study, four horses chewed on the right and
three on the left and they did not change chewing sides during data collection. The
number of cycles a horse will chew on one side before switching to the other side has not
been documented to the author’s knowledge. However, horses without malocclusions
have been observed to chew on both sides. If a malocclusion restricts a horse from
chewing on one side, continuous chewing on the other side will cause the malocclusion to
worsen. It is necessary for an equine dentist to remove these restricting malocclusions in
order to allow the horse to chew with adequate lateral excursion. If problematic dentition
is neglected, malocclusions can propagate into more serious problems such as buccal and

lingual trauma and peridontal disease.

72

4.3 Mandibular Euler Angles During Chewing:

In biomechanics, movement descriptions provide a transition from mechanical
terminology to anatomically meaningful terms. For example, when evaluating the
motion of the tibia relative to the femur, the ﬁrst joint rotation is described as
ﬂexion/extension, the second as ab/adduction, and the third as internal/extemal rotation.
This terminology, however, is not applicable when describing the motion of the mandible
relative to the skull since rigid fusion of the mandibular symphysis precludes independent
motion of the left and right sides. The opening and closing of the jaw can logically be
call ﬂexion and extension, but the rami of the mandible cannot show ab/adduction, which
refers to motion away from or towards the midline of the body or internal and external
rotation, which refers to a rotation towards and away from the midline of the body. Pitch,
roll, and yaw are commonly used in the aerospace ﬁeld to describe the 3-D motion of
aircrafts. In equine biomechanics, Fredrickson et al. (1971) used this terminology to
describe the three-dimensional orientation and motion of the equine hoof during
locomotion. Ostry et al. (1997) and used pitch, roll, and yaw to describe the rotations of

the human mandible.

The masticatory cycle in herbivorous mammals is generally considered to consist of three
events: the opening stroke, the closing stroke, and the power stroke. Collinson (1994)
described the opening stroke as a downward hinge movement of the mandible, mediated
by the gliding action of both condyles and the closing stroke as an upward movement

combined with a rotation of each condyle in its glenoid cavity. This study showed that

73

not only is there a downward hinge movement (a pitch rotation 01 about the transverse
horizonal axis) during the opening phase, but slight rotations also occur about the other

tWO axes.

As the horses chewed, the pitch angular velocity was positive as the jaws opened and
negative as the jaws closed. The roll and yaw angles were small compared to the pitch
angle during the opening phase of a horse chewing on the right. The roll rate was
negative, which was a negative rotation about the longitudinal axis resulting in a
clockwise roll of the mandible when viewed from the front of the horse, and the yaw rate
was positive (a slight positive rotation about the vertical axis). In one horse, the yaw was
negative early in the opening phase, but then became positive near the end of the opening
phase. During the closing phase, the extent of roll was small compared to pitch and yaw
and was generally positive for a horse chewing on the right, corresponding to a counter-
clockwise rotation when observed from the front. The yaw of a horse chewing on the
right was negative during the ﬁrst portion of the closing phase, followed by a positive
yaw during the second portion of the closing phase. The positive yaw corresponded to
the grinding portion, or power stroke, of the cycle where the pitch angle was small and
had little variation. The slope of molar table angle likely dictates the extent of roll angle
during the power stroke: a steeper molar table angle will result in more extensive

mandibular roll and a more level molar table will have less.

A horse chewing on the left (Figure 69 in Appendix C, for example) had a positive roll

rate (mandible rolled counter-clockwise when viewed from the front) and a negative yaw

74

rate (mandible moves to the right) during the cycle’s opening phase. During the closing
phase, the roll rate was generally negative (mandible rolled clockwise) and its magnitude
was small compared to pitch and yaw. The yaw angle increased during the ﬁrst portion
of the closing phase, followed by a negative yaw rate during the second portion, again
corresponding to the grinding phase. The left molar table is sloped in the opposite
direction to the right molar table and consequently, the mandible rolls in the opposite
manner when compared to the right. Similar to chewing on the right, the negative yaw

corresponded to the power stroke of the cycle.

In order to completely describe the mandibular motion, not only do the rotations of the
mandibular coordinate system need to be provided, but also the displacement of the

coordinate system.

4.4 Mandibular Coordinate System Displacement:

During the opening phase of a horse chewing on the left, as seen in Figures 23-25, the
origin of the mandibular coordinate system moved in the negative z-direction (ventrally)
and slightly in the positive x-direction (rostrally). In general, there was little
displacement in the y-direction. During the closing phase, the mandibular coordinate
system displaced in the positive z-direction (dorsally) and slightly in the negative x-
direction (caudally). The coordinate system displaced in the positive y-direction early in
the closing phase, followed by a displacement in the negative y-direction. The change in

displacement direction likely corresponds to the power stroke of the chewing cycle.

75

A horse chewing on the right has the same general trends as a horse chewing on the left,

except the sign of the y-displacement is reversed.

In order to completely describe a rigid body’s orientation in space, the three rotation and
three displacements need to be described. The mandibular rotations and displacements
sufﬁciently describe the mandible’s orientation during the chewing cycle. However, the
location of the midline mandibular marker provides an additional visual aid in describing

the motion.

4.5 Midline-Mandibular Marker Displacement:

Plotting the midline-mandible marker serves as a visual aid in describing the mandibular
motion. The mandible’s motion is completely described by the three rotation and three
translations; however, the resulting motion is not obvious. The location of the virtual
midline-mandible marker was plotted in all three planes. During the opening phase, the
midline-mandible marker of a horse chewing on the right moved in the negative 2-
direction (ventrally) and in some horses, slightly to the left (positive y-direction) until the
maximum pitch angle was obtained. The displacement in the x-direction was minimal,
but tended to be in the negative direction (caudally). During the closing phase, the
midline-mandible marker moved to the right (negative y- and positive z-directions) until
the maximum lateral excursion was obtained and occusal contact was established. The

mandible then slid to the left (positive y-direction), back to the original position during

76

the grinding process. The midline-mandible marker slightly moved either in the positive
x-direction (rostrally) during the entire closing phase (two horses), or continued in the
negative x-direction (caudally) for the beginning portion of the closing phase, then
moved in the positive x-direction (ﬁve horses). When observing the midline—mandibular
marker motion in the z-y plane (Figures 18-19), it is likely that the slope of the cheek
teeth’s occlusal surface determines the slope of the path ﬁ'om location #3 to #1. This can
be conﬁrmed by comparing actual measurements of the horse’s teeth to the slope on the
graphs. These patterns were more clearly indicated in some horses than others, but the
general trends were similar. These results indicate that the mandible’s center of rotation

is slightly rostral and ventral to the mandibular coordinate system.

A horse chewing on the left has the same general trends as a horse chewing on the right,

except the sign of the y-displacement is reversed.

4.6 Comparisons to Previous Work:

4.6.1 Lateral Mandibular Displacement (Y -displacement):

Two previous studies have examined the lateral excursion of the equine mandible. Leue
(1941) created a molograph that ﬁtted over the rostral portion of the horse’s upper and
lower jaws and traced the mandibular path while chewing grass, oats, and bran (Figure
4). The mandible location that the sketches were created from is not indicated nor are the

excursion values in Becker’s (1962) citation of Leue’s study. Dixon (2000) stated that

77

the excursion values were 60, 38, and 23 mm while chewing grass, oats, and bran
respectively. These values were obtained by simply measuring the distances on the
sketch provided in Becker (1962). Unfortunately, the sketch does not necessarily
represent the actual excursion values as the curves are much too smooth and the sketch
could have been resized for publication purposes. Therefore, the sketch appears to be just
a representation of the general chewing pattern rather than an actual chewing cycle. The

sketch can be used to make basic comparisons between three different feeds.

Using the relative excursion values of the excursion based on Leue’s study provided by
Dixon (2000), the lateral excursion while chewing bran was 38% of the lateral excursion
while chewing grass. In the present study, the lateral excursion while chewing pellets
was 77% of the lateral excursion while chewing hay. Leue stated that a horse would
chew with more lateral excursion when the moisture content of the food is increased and
with a less when the ﬁber content is increased (cited by Baker and Easley, 1999). Grass
has a much higher moisture content than hay and bran has more ﬁber than pellets. In
addition, the particle size of bran is smaller than the size of pellets. Leue (1941, cited by
Dixon, 2000) suggested that ﬁbrous food such as hay or grass required the mandible to
move laterally to its full extent to allow complete grinding, whereas smaller particles
could be more easily retained on the occlusal surface and therefore required less lateral
excursion to adequately grind the food. This combination of factors probably contributed
to more extensive lateral excursion while chewing grass compared to hay, and reduced

lateral excursion while chewing bran compared to pellets. Consequently, the lateral

78

excursion while chewing pellets was a greater percentage of the excursion while chewing

hay compared to the relationship between bran and grass in Leue’s study.

Collinson (1994) reported incisor displacement to be 44—45 mm while chewing forages.
The displacement was measured by marking the upper and lower lips with a continuous
line at the junction between the ﬁrst incisors, recording the mastication sequences with a
video camera, and measuring the displacement from the recording. As stated previously
in regards to Baker and Easley’s (1999) efforts to track the mandibular motion during
chewing, the lips consist of highly mobile soft tissue and cannot be classiﬁed as rigid
bodies. Therefore, this method of measuring the incisor displacements is regarded as an

approximation only.

The mean lateral displacement (y-displacement) in this study, measured at the virtual
midline mandibular marker, was 19.87 mm and 15.38 mm while chewing hay and pellets,
respectively. As previously described, the virtual midline-mandible marker was created
at approximately the level of the ﬁrst molars. Therefore, this virtual marker does not
represent the motion of the incisors. The x-distance between the condyles and virtual
marker is approximately half the distance between the condyles and the incisors.
Consequently, obtaining lateral excursions of the virtual marker that are approximately

half of those measured at the incisors by Collinson is reasonable and proportional.

Collinson (1994) reported the mean width of the lower fourth premolar, the largest tooth

in the molar row, to be 1.64 cm measured from 16 horses. Although the upper check

79

teeth are slightly wider than the lower, the lateral excursion while chewing hay was
approximately 2 cm, which is sufficient to wear nearly the entire occlusal surface. The
lateral excursion while chewing pellets, however, was approximately 1.5 cm, which is
insufﬁcient to completely wear the opposing occlusal surface and consequently, sharp
enamel points can develop. If the horse’s diet primarily comes ﬁ'orn concentrates, an
equine dentist must regularly treat the horse to prevent malocclusions ﬁom developing.

Figure 27 depicts the interaction between the upper and lower enamel ridges of a left

cheek tooth while chewing on the left.

   

(a) (b) (C)

Figure 27 : Schematic of enamel ridges for a left cheek tooth while chewing on the left.
Black = upper molar, Grey = lower molar (a) maximum lateral excursion (start of
grinding phase) (b) mid grinding phase (c) end of grinding phase (resting position)

80

4.6.2 Mandibular X and Z-Displacements:

As discussed above, lateral excursions obtained in this study comply with Collinson’s
study (1994) that measured lateral excursion at the incisors. The author is not aware of
studies that also measured the displacements in the x and z-directions. The displacements
in the x, y, and z-directions were signiﬁcantly larger while chewing hay than pellets.
This is likely due to the feed-particle size as Leue (1941) described since the dry matter
contents are similar. In order to completely grind large food particles, the mandible must
open and displace more than when chewing smaller particles. This study shows that not
only does more lateral excursion occur while chewing hay, but there is also more
mandibular displacement rostro-caudally and dorso-ventrally when compared to chewing
pellets. Accordingly, the area encompassed by a cycle is signiﬁcantly larger while

chewing hay compared to pellets.

4.6.3 Mandibular Chewing Velocity and Frequency:

Collinson ( 1994) reported the absolute velocity measured at the fourth premolar to range
from 104 mm/sec for high ﬁber hay (75% ﬁber) to 85 mm/sec for low ﬁber hay (55%
ﬁber). These values are average velocities for the entire chewing cycle, obtained by
using the displacement values measured from the lips and cycle duration values to
estimate the velocity at the incisors. Incisor tooth velocity values were then used to
estimate the velocity attained by individual molar teeth during mastication (Collinson,

1994). Collinson found molar velocity to be proportional to the distance from the TMJ,

81

whereby the velocity of the third molar was approximately half the velocity of the second
premolar. The fourth premolar is the tooth just rostral to the ﬁrst molar, which is where
the velocity of the virtual midline-mandible marker was measured. This study obtained
mean absolute velocity values, measured at the virtual midline-mandibular marker, of
77.63 mm/sec for hay with 44.6% ﬁber and 79.03 mm/sec for pellets with 30% ﬁber,
which follows the trend that Collinson described. There was no signiﬁcant difference in

the velocities of hay versus pellets.

The chewing frequency reported by Collinson ranged from 1.14 Hz for high ﬁber (75%)
forages, 1.15 Hz for medium ﬁber (65%) forages and 1.16 Hz for low ﬁber (55%)
forages. By measuring masseter muscle activity with electromyography, chewing
frequency was determined. The chewing ﬁ'equencies Collinson reported were not highly
dependent on ﬁber content. The forage length was 3-12 cm, a typical range for hay. In
this study, the mean frequency was 1.18 Hz while chewing hay, which is similar to
Collinson’s ﬁndings, and 1.48 Hz while chewing pellets. Chewing frequency appears to
be dependent on particle size; the larger particle size of hay requires more time to

completely grind on the occlusal surface compared to pellets.

4.6.4 Mandibular Coordinate System Translation and Rotation:

The author is unaware of any previous study that examines the translation or rotation of

the equine TMJ.

82

4.6.5 Human Studies

In a study performed by Visscher et al. (2000), the kinematics of the human mandible for
different head postures was investigated. The head position was found to inﬂuence the
mandibular kinematics, probably due to the differences in mandibular loading. Although
the horses were fed from the same location, future studies should record chewing cycles
for different head postures to determine if the motion varies with head position. Gallo et
al. (2000) described the mandibular motion during mastication through the helical axis
pathway. In this study, three translations and three rotations described the mandibular
motion because the results give a more intuitive description of the motion. Yatabe et al.
(1997) used the kinematic center of the right and left condyles as a reference point for the
reconstruction of condylar movement paths. In the present study, the mandibular
kinematic center was established halfway between the two condyles and the motion of
that location was observed relative to the skull coordinate system. In order to make
comparisons to human condylar motion based on Yatabe’s ﬁndings, the equine condylar
motion can be observed by creating a mandibular coordinate system at each condyle and

observing translations and rotations at that point.

83

5. Conclusions and Recommendations:

A limited number of veterinarians and specialists have dedicated their lives to improving
equine dental health and understanding the development of malocclusions. On-line
equine dentistry groups are ﬂooded with discussions on dentistry techniques and theories
as to what the primary contributing factors that lead to malocclusions are. Most
professional equine dentists would agree that horses chew forages such as hay differently
than concentrate feeds and they believe that the degree of lateral excursion is an

important factor in minimizing malocclusions.

This study quantiﬁed the three-dimensional motion of the equine TMJ while chewing hay
and pellets. The results provide base-line data, including the angular and linear
displacements of the TMJ during the chewing cycle. The location of a virtual midline-
mandible marker was plotted to serve as a visual” aid in describing the mandibular motion.
The horses examined did not have any malocclusion and they encompassed a broad range
of breeds, sizes, and ages. In addition, the three-dimensional Motion Analysis tracking
system is much more accurate than the tracking points on the lips as Collinson (1994) and
Baker and Easley (1999) have done in two dimensions. Therefore, the results ﬁ'om this

study more adequately represent the general, normal 3-D motion of the equine TMJ.

The paired t—test tested the null hypothesis, that there is not a signiﬁcant difference

between the mean values of the variables that measure mandibular motion in horses

chewing hay versus pellets, and the results allow the null hypothesis to be rejected.

84

Therefore, the experimental hypothesis is accepted. While the results indicate that
chewing motion is inﬂuenced by feed-particle size, the data collected did show that for
some horses in the sample, this was not the case. Nevertheless, the measured variables
were signiﬁcantly different when statistics were run over the complete group of seven

horses. Coarse, ﬁbrous feeds show a more extensive chewing motion than pellets.

The knowledge gained through this study can be useful to the feed industry. Products
with larger feed particle size and the current nutritional value per kilogram need to be
developed to encourage horses to chew with more lateral excursion while maintaining
adequate nutrition. Current products are designed for their nutritional value, but the
small particle size of most concentrates does not encourage horses to chew with the

extent of lateral excursion that would prevent sharp enamel points from developing.

Having a description of the TMJ motion during normal chewing, it would be interesting
to now examine horses with malocclusions. The malocclusions would be evaluated and
categorized by an equine dentist, and the deviations from the normal patterns would be
noted. The dentist would then treat the horse to remove the malocclusions and the horse
would be re-evaluated at post-treatment intervals to observe any changes in the chewing
pattern. The techniques that resulted in improved chewing (more extensive lateral
excursion) would be documented and shared with the equine dentistry community to

promote equine dental health.

85

In the future, kinematic studies should include a broader range of feed types with varying
ﬁber and moisture content to determine how ﬁber and moisture inﬂuence the chewing
cycle. Bone pin, magnetometer, or 3-D ﬂuoroscopic studies should be performed to
determine how the skin displaces over the bony landmarks selected for marker placement
during chewing. By adjusting for skin displacement, the results will more accurately

represent the TMJ motion.

86

Appendix A:

Location of midline-mandibular marker relative to skull coordinate system viewed in
all three planes for all horses.

87

 

 

 

 

 

 

 

 

 

 

 

 

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for horse #1 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

88

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

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for horse #1 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

89

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X-axis (mm)

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Y-axis (mm)
Pellets
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Y-axis (mm)

for horse #1 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

9O

 

10

Figure 30: x-y location of midline-mandibular marker

 

 

 

 

 

 

 

 

 

 

 

 

I I I
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5 ~ — Closing Phase
’2‘
0 _ ..
E
V
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-20 -10 40 50
Y-axis (mm)
Pellets
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”-1. :93: — Closing Phase
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Y-axis (mm)

30 40

Figure 31: z—y location of midline-mandibular marker

for horse #2 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

91

 

 

 

 

 

 

 

 

 

 

 

I I I I
.-.. .. Open'ng Phase
5 ” — Closing Phase 7
’5‘
0 ~ _
E
V
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26
N -10 r -‘
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-30 -2o -10 30 4o
X-axis (mm)
Pellets
r I I if, , 1 I
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>491 — Closing Phase
A 0 ~ “£2,
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10 20 30

 

 

 

 

 

 

X-axis (mm)

Figure 32: z-x location of midline-mandibular marker
for horse #2 chewing on the left

Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

92

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

T l 1
~— Opedng Phase
20 L — Closing Phase —
73‘
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Pellets
T T T l l l ‘ '7 l L I
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20 _ g ‘ — Closing Phase *‘
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Y-axis (mm)

Figure 33: x-y location of midline-mandibular marker

for horse #2 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

93

 

 

Z-axis (mm)
3. 3 3»

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o

Z-axis(mm)
3 3 do 61 «'5 lb 0

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

l i e- T l 1
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1jg‘ ' — Closing Phase
. k": f ‘
L—
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-20 -10 0 10 20
Y-axis (mm)
Pellets
r l l l I
P ~~- Opering Phase
_ — Closing Phase
I l l '_4ummumn"‘ ‘1 1 1 l
-20 -15 -10 -5 0 5 10 15
Y-axis (mm)

Figure 34: z-y location of midline-mandibular marker
for horse #3 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

94

 

Z-axis (mm)

Z-axis (mm)

1. .1. .
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-10
-12

 

 

 

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- Opening Phase
— Closing Phase

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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X-axis (mm)
Pellets
T T f T I I
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— Closing Phase
4
i l L l l 1
-25 -20 -15 -10 -5 0 5 10

X-axis (mm)

Figure 35: z-x location of midline-mandibular marker
for horse #3 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

95

X-axis (mm)

X-axis (mm)

3.3.3.3
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Hay

 

 

 

 

 

 

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Y-axis (mm)
Pellets

15

 

 

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Figure 36:

-6 -4 -2 o 2 4
Y-axis (mm)

for horse #3 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

96

x-y location of midline-mandibular marker

Z-axis (mm)

Z-axis (mm)

 

I
(II
T

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A

O
T

 

 

 

 

 

 

-5 o 5 1o 15 20 25 30
Y-axis (mm)
Pellets

 

 

 

 

mopLungpmsé
—ClosingPhase F

 

 

 

 

 

 

25 30

Y-axis (mm)

Figure 37 : z-y location of midline-mandibular marker
for horse #4 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

97

Z-axis (mm)
in

Z-axis (mm)
1.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

T TV T T T L T
«M Opening Phase
1'
l
l
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X-axis (mm)
Pellets
T f T I l
Opening Phase a
— Closing Phase
4
l L 1 l l
-15 -1o -5 15 20 25

 

X-axis (mm)

Figure 38: z-x location of midline-mandibular marker
for horse #4 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

98

.15
O
T

X-axis (mm)

(D
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a)
T

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X-axis (mm)
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' - ., ' .. .. ~- 114‘
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Y-axis (mm)
Pellets

 

 

 

 

 

  
 
     

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-5 0 5 ___ “1'0 , 15 20 25
Y-axis (mm)

Figure 39: x-y location of midline-mandibular marker
for horse #4 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

99

 

 

 

 

 

    

 

 

T T 7 I I I
----- Opening Phase
0 — — Closing Phase
E ’5 '— “119$ / \
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-40 -30 -20 -10 o 10 20 30
Y-axis (mm)
Pellets
o — ' ‘ I

 

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— Closing Phase

 

 

 

l
U"
T

 

Z-axis (mm)
3

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10 20
Y-axis (mm)

Figure 40: z-y location of midline-mandibular marker
for horse #5 chewing on the leﬁ
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

100

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 T T i F
W. Opening Phase J
0 _ — Closing Phase
A
E -5 i— e‘ .1
3
.2 -10 h _
N -15 ~31, ~
-20 P J 1 1 a; l l .—
-4o -30 -20 1o 20
X-axis (mm)
Pellets
o __ i i T 1
-—--— Opening Phase
— Closing Phase
E '5 * ‘
E
v
.Q -10 — ~
Si
-15 _ _
-40 -30 -2o -10 o 10
X-axis (mm)

 

 

Figure 41: z-x location of midline-mandibular marker
for horse #5 chewing on the leﬁ
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

101

X-axis (mm)

X-axis (mm)

I
(1'

J.
a:

 

 

 

1 I
"*'" Opening Phase
— ClOSIng Phase

 

 

 

 

M It lililllllﬂ
"‘Q."’.’?f I I

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-30 -25 ~20 -15 -10 _5 0 5 1o 15 20
Y-axis (m m)
Pellets

 

 

 

   

 

 
     
 

 

 
 

 

 

-8 t X
ﬁl-Cﬂ-I-ﬂ-I-J’
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Y-axis (mm)

Figure 42: x-y location of midline-mandibular marker
for horse #5 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

102

 

Z-axis (mm)

 

Z-axis (mm)

 

 

 

 

 

 

 

 

 

  
     
   

 

 

 

 

 

 

o P—
-5 r
-10 _.
-15 ~ J .. ~ ._ 1
Y-axis (mm)
Pellet
0 H l l l 1 ‘77 1 1 I 1 _
I ’ ‘ ,w-S‘t" * “- Opening Phase
-2_ if, ““V’a —ClOSlngPhase ~
I u \ - ~
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l 1 L 1 L i 1
-2o -15 -1o -5 o 5 1o 15 20
Y-axis (mm)

for horse #6 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2

103

Hatched line = Trial 3

Figure 43: z-y location of midline-mandibular marker

 

 

Z-axis (mm)

 

I T I

 

.-..,. Opening Phase _

 

 

 

 

 

Z-axis (mm)
3 8 a. a. A r'o

 

 

 

 

 

 

 

 

 

_ — Closing Phase
*' 1 1 1 1 1 1 1
45 -40 ~35 ~30 -25 -20 -15 -10 -5 0 5
X-axis (mm)
Pellets
I T W v' T l

- Opening Phase
P — Closing Phase
L
_.L___~ _- _. L l l 1
-30 —25 -20 0 5 10

 

X-axis (mm)

Figure 44: z-x location of midline-mandibular marker
for horse #6 chewing on the leﬁ
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

104

 

 

  

 

 
   

 

 

 

 

 

 

 

 

 

  

   
    
  
   

   

 

 

 

 

 

 

‘10 T f T I I I
.... ' m Phase
— Closing Phase
A
E -15 T
E,
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x Ii~ .5
'25 ' .' _
1 1 ./'/l 1 L 1 1 1
-30 -25 —20 ~15 -10 -5 0 5 10 15 20
Y~axis (mm)
Pellets
l T l f v-g ‘ ' I L
‘4 ...“ Opeung Phase
. — Closing Phase
A -6 q
E .8 u"“\\““u”.“umm""1
v . T
V v‘muoﬁutﬂ \““‘\\ .
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53-12 ‘‘‘‘‘‘‘ _
-14 _
-16 1 g 1 1 _
-20 -15 -1o -5 o 5 10 15 20

Y~axis (mm)

Figure 45: x-y location of midline-mandibular marker
for horse #6 chewing on the leﬁ
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

105

Z~axis (mm)

c'nL

Z~axis (mm)
ch 1»

do

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Y~axis (mm)
Pellets
j T I I I
..... 090N119 Phase
”$35!“ — cm“ ”W 1
b ’ '
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w \ 1‘ ’3‘ aummlgt1¥§ f. 4*:2:Q‘ ,‘ ...... ;;;’r
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Y~axis (mm)

Figure 46: z-y location of midline-mandibular marker
for horse #7 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

106

Hay

 

 

 

 

 

 

 

 

 

 

 

    
 

 

 

 

 

    

 

 

Y I T l l T I I— T
4 F m Closl "9:2.”
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~20 ~15 ~10 ~5 0 5 1O 15
X-axis (mm)
Pellets
l T l l l l L I
'4 ’ I 'l -- Opeting Phase _
. ’. —- Closing Phase
A_ _ * __”__,,_, '#’~-v ,go‘l.
E 5 7 > ~4- .. - _ «I: ro"’3-
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~16 ~14 ~12 ~10 ~8 ~6 ~4 ~2

X-axis (mm)

Figure 47: z-x location of midline-mandibular marker
for horse #7 chewing on the leﬁ
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

107

 

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A
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.4

 

 

 

 

1.... l I r
5'.91|I,W' “H": -..1. .
“6‘”??? 1‘3ﬂhlllnvuimt " Opeﬂng Phase
0 v “"“m —- Closing Phase
‘ l ‘

 

 

 

 

 

 

 

   

 

 

 

 

 

E
-5 d
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.2 -10 — _
5?
x ~15 - q
-20 l— -‘
l l \ l L
-50 -40 ~30 -2o -10 0 10 20 3o
Y~axis (mm)
Pellets
-8 .— 1 f 1 I
w‘” """ Opening Phase
1° '~‘-----.' — Closing Phase 1
- ’— o nuncrﬂ': .,
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£42 - q
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-16 b r '0 : .um “11:: I...‘“\.““\““\\\ .- V‘k._ ‘ -4
1 ruuu‘“ 1 J l l l
-20 -15 _10 5 o 5

Y~axis (mm)

Figure 48: x-y location of midline-mandibular marker
for horse #7 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

108

Appendix B:

Location of mandibular coordinate system relative to skull coordinate system viewed
in all three planes for all horses.

109

Z~axis (mm)

Z~axis (mm)

1 I
N d O

I
U

GAMMA“

I
.8

 

 

 

I I
--—~-- Opering Phase
— Closing Phase

 

 

 

 

l.-

 

 

Y~axis (mm)
Pellets

 

 

 

I I
---~— Open'ng Phase
— Closing Phase ~

 

 

 

 

p.
h
I—

 

Y-axis (mm)

Figure 49: z-y location of mandibular coordinate system
for horse #1 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

110

Z~axis (mm)

Z~axis (mm)

 

 

  

 

 

 

 

 

 

O
-— "
.U-u-Iucuu".

 

l 1 i L l 4 l l l

 

-2 o 2 4 6 8 1o 12 14
X-axis (mm)
Pellets

 

 

 

 

 

 

 

 

5 T m r r 11
4 F H
3 P .1
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1‘"
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f """""""" ..'.'.'.'mm- \\\ ‘5'",
I, l... l * \
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-2 o 2 4 6 8 1o 12 14 16 1a
X-axis (mm)

Figure 50: z-x location of mandibular coordinate system
for horse #1 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

ll]

X-axis (mm)

0

4.5.1.
ONb

X-axis (mm)

 

 

 

T I
- Opening Phase
— Closing Phase

 

 

 

 

 

 

 

 

 

 

 

 

 

 

l L l l l l l 1
~20 ~15 ~10 ~5 10 15 20 25
Y~axis (mm)
Pellets

T T l T l r -4
~ Opening Phase
— Closing Phase L

.1
l l l l l 1
~15 ~1 0 ~15 10 15 20

 

Y~axis (mm)

Figure 51: x-y location of mandibular coordinate system
for horse #1 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

112

m

G)

Z-axis (mm)

C

I
N

a

Z-axis (mm)
0 N

I
N

N
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Y-axns (mm)
Pellets
I I I I I . I
r m- Opeling Phase ~
— Closing Phase ‘
MW“ » 4‘“ -. v
— "m ghmiaml Wt \llm,‘ﬂ
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Y-axis (mm)

Figure 52: z-y location of mandibular coordinate system
for horse #2 chewing on the leﬁ
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

113

 

 

 

 

 

      

 

 

 

X-axis (mm)

ﬂ 1 I I ‘ j
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X-axis (mm)
Pellets
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Figure 53: z-x location of mandibular coordinate system

for horse #2 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

114

 

 

 

 

 

 

I
----—- Opening Phase
— Closing Phase

8

 

 

 

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U
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X-axis (mm)
8

 

 

 

 

 

 

 

 

 

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1 1 1 1 1
-3O -20 -10 0 10 20 30 40
Y—axis (mm)
Pellets
l l l j r l '_" T I I
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20 ” j" — Closing Phase "
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I
X 0 h
-5 l—
1 l 1 1 1 1

 

 

 

 

1
1o 20 3o 40
Y-axis (mm)

Figure S4: x-y location of mandibular coordinate system
for horse #2 chewing on the leﬁ
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

115

Z-axis (mm)
3 ('0 6o 4:

-6

-7

Z-axis (mm)

1.
o

 

 

 

--— Opedng Phase
— Closing Phase

 

 

 

 

 

-10 -5 .2;
Y-axis (mm)
Pallets

 

 

 

 

 

 

 

 

 

Figure 55: z-y location of mandibular coordinate system
for horse #3 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

116

 

 

 

 

 

 

 

 

 
  

 
 

 

 

    
     

 

 

-7 _
E ’3”
-9 _
E
.2 -10 —
3 -11 -
I
N -12 — a ,,
a' ’ ‘ a J; ,’
'13 ”41% ' I "1'..,/"‘».H,_ . .
w ‘ . 1 l l
-20 '15 -10 -5
X-axis (mm)
Pellets
I I ‘ r I.-
-51. "fl-"a ’,
.- ‘y
E '7 ’ (‘1 ”'5'" \ s,
g 1 ‘ ‘ £311:ch -- 3
in '3~ a. . ‘
5 -9_
N \
'10 L ~\\W‘\ ,s‘ "mums“
.1 Ht.
J In L: 1 1 1 L I 1 1
-16 ~14 -12 -10 -8 -6 4 -2

X-axis (mm)

Figure 56: z-x location of mandibular coordinate system
for horse #3 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

117

 

 

T I

 

.._ Opening Phase

 

 

 

 

 

 

 

 

 

 

 

 

 

 

‘5 — Closing Phase
’5‘
-10
E
V
in
g -15
I
X
-20
1 1 1 1
-30 -20 20 30
T T W T J
-2 Opening Phase
— Closing Phase
E -4
E -6
v
.2 4’
$-10
X
-12
-14 1 1 1 1 1
-20 -15 -10 10 15 20

Y-axis (mm)

Figure 57: x-y location of mandibular coordinate system

for horse #3 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

118

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  
 
 

      
  
  

  
 

 

 

 

-2 >— ‘
-3 _
A
E
5+ _
.9
a -5 ~ A
I
N
-5 _ d
a 10 12 14 16 1a 20
Y-axis (mm)
Pellets
l 1 T 1 . 1 1 I
" , --- Openlng Phase
-2 ’- > /.-'z,‘ "1 — mm m“
A 1 ‘\
E - — ' “ 1 «mm \\“‘~ —
E 3 ‘ . 7.1 ....~'_‘"‘ .1 ‘ ‘ 1 u waxwwiiul ' munmm_
‘0'; ‘I ”S A ‘ "Jr-"- 4; 171%“; 13'2‘3“m1111Wuiufii . . ' . " WK“
-.---~€.-“_X.”” U... , ' ‘ . 1. ‘ ‘ ,
N. 5 , "huu ' ~ _ ‘
- ‘ ‘ “1:155:33:sz
-5 1 1 . .. 1 1 1 1 1 _
4 6 a 10 12 14 16 1a

Y-axis (mm)

Figure 58: z-y location of mandibular coordinate system
for horse #4 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

119

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

-2 >— T 1 I I ’IP"' I t 1 ~
~ :’ .' --~ Opening Phase
N ‘ ' —
-3 ~ ‘1 m’r ~~ ; Chane Phase
I ‘5 I
E ' "
. m _
é" ” 1 ﬁg:
w
Ia-s~ —
I
N
-6 »- —
1 J
0 12
X-axis (mm)
Pellets
T T T T T T 4
2 «~— Opering Phase H
' .. .1 - Closino Phase
3‘ J’“ ' ""Nu‘f.
E . -' " e '3. WM ‘ “a“ u"
E‘sb 1. f ’ ’ " ' ' d
.h - “w i “ ’ .. ".-
V ‘\ 1””? I. g“ . ‘1 m
.w .4 1. ‘ .;~ ~ ‘ 1’1 ‘\“ —1
g NIP-n '~ ‘~~ ' v1 1 o‘“ .»
‘~ \ .~~~ I!" ‘ ‘3 41
Kl 5 .-.-:~\;::221;f
' ‘— >.'.-- g--."" _
-nA-V I '1. ._ 2'.
”971‘,
1' ‘ "”
'6 "1 1 l 1.4 1 1 1 1
-4 -2 0 2 4 6 8 10

X-axis (mm)

Figure 59: z-x location of mandibular coordinate system
for horse #4 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

120

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10 l 1
~-—- Opening Phase
-— Closing Phase
A 8 T d
E
v 6 ,— 1
.9
—
2 .4
0 5 25
Y-axis (mm)
Pellets
l T 1 T T 1
8 _ _...._... Opening Phase _
— Closing Phase
A 6 - q
E
'5 2' W 1 ‘
I o _ " :ﬁkﬁi“ ’1 "'\ I _1
x I, I 'l “ r
‘2 ” ”9‘93” -
1 1 {',¢' 1 1 1 1 1
-5 0 5 10 15 2O 25 30
Y-axis (mm)

Figure 60: x-y location of mandibular coordinate system
for horse #4 chewing on the left
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

121

 

O M «b O)
T

 

 

 

 

 

 

 

 

 

A
E
E,
.92 P
6 -2 —
141
-4 _
.5 p
-20 - -1-5 0 5 1o 15
Y-axis (mm)
Pellets
l T 1 T T l A I
- Opening Phase

1
.5
T

I
N
1

Z-axis (mm)
L 1'»

1
(1|
1

 

 

— Closing Phase

 

 

 

 

.tﬂf";§ n
.- 11111" 11111111 ~’ ' ﬁg! .: I wMVé‘mmu
30‘ ‘ r 1111!» :3... “"““I“
:1 ' o
D :11! 1"l1'u“ ‘‘‘‘‘‘ 1 1 1
-10 -8 -6 -4 -2 0 2

Y-axis (mm)

Figure 61: z-y location of mandibular coordinate system
for horse #5 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

122

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

       
 

 

 

j a.
6 ~ 1 ' Opening Phase ”
4 _ — Closing Phase
A
E 2 — 5
E
.2 ° ’
15 -2 — _
I
N .4 _ d
-6: 1 ”M'ﬁimm'1MM": 1 1 1 1 1 T
-20 -15 -10 -5 o 5 1o 15 20
X-axis (mm)
Pellets
I 1 I I
0 .—
E
E -2 h
v ‘1‘
.9 - . .
g '4 1' _ "1' -.3‘-::11le _
N. 1911“ )1 ' :M"“:‘mq'::‘ﬂ"mmeﬁfhﬂmwu
-5 Z" 5
1 1 1 1 1
-15 '10 -5 o 5
X-axis (mm)

Figure 62: z-x location of mandibular coordinate system
for horse #5 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

123

X-axis (mm)
o 8 8

L.
o

X-axis (mm)
3 ('11 o 01

.2.
(.n

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

.—f T T T T
---- Opening Phase
— Closing Phase
1 a
1 1 1 1 1
-60 -40 -20 20 40
Y~axis (mm)
Pellets
T T T ' T I I
*---~ Opening Phase
P — Closing Phase 1
"‘ '1
1. _.
’— 1 1 1 J 1 1 A
-40 -30 -20 -10 0 10 20 30

Y-axis (mm)

Figure 63: x-y location of mandibular coordinate system
for horse #5 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

124

Z~axis (mm)

Z-axis (mm)

a. $

N

 

O
T

I
N
T

1
m

 

 

. A 1
5g . 31,.” “w Opening Phase
1, — Closing Phase

 

 

 

 

‘17.; ' ' ,
y“ 41
‘\"’ - I n -‘
‘ .
‘\\‘ .Pn‘ ‘ 1I~ ““‘\‘ ' . . ‘(
‘ \\\Q‘|' 1‘“ T ‘w' :E‘A'
'

:o \‘ v
\ ' i,
811111 ' ~
1

 

 

-15 -1o -5 o 5 1o
Y-axis (mm)

 

4165611511111:
IIIIII

 

Pellets

T T l V T T

 

 

 

 

 

 

 

Y-axis (mm)

Figure 64: z-y location of mandibular coordinate system
for horse #6 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

125

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2 T ﬂ I v_1.\.. #7,, ﬁk 1
---OpeningPhase
0 _ — Closing Phase .
A
.g 4 +- ia’ 4
h'l -6 ~ —
-3 _ .4
-30 -5 0
X-axis (mm)
Pellets
-2
E-B
E .4
V
.9 -5
g 6

 

 

 

 

X-axis (mm)

Figure 65: z-x location of mandibular coordinate system
for horse #6 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

126

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

l l l l I
-5 a ------ Opening Phase H
— Closing Phase
A
E -10 ~ _
E
V
g -15 ~ —
x. 1:40.93
-20 .— ‘23:...“ —i
l l l l 1
~30 -20 -10 10 20
Y-axis (mm)
Pellets
0 .. V l l J I
~-~- Opening Phase r
— Closing Phase
E -5 ~ .4
E,
.3 -10 ~— q
I
X
-15 _ ..
l l L 1
~20 -10 10 20 30

 

Y-axis (mm)

Figure 66: x-y location of mandibular coordinate system
for horse #6 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

Z-axis (mm)

Z-axis (mm)
lb

5.

 

 

 

 

ON &
j

I
0')
T

 

 

 

 

Y-axis (mm)
Pellets

 

 

 

 

 

 

 

 

r I I l I
~—- Operlng Phase
‘ I" — Closing Phase
.4 #— ..*‘\ it, v .__ Q -l
‘ z ‘ ‘6 z x ’ l o- x \1 .F ‘5“ f
l‘ ~.“.. \___' ~ ...a*’- *" r
b 5"“ F“ glllllllllga . V‘ “ $§~Iﬂd‘,~--,‘:"d 5:,
' : M ‘w "' I v r s -" " a 'O
-6 _ ‘. ‘ l ' " ,a ‘ “""-'\-“~ 4 33“?“ o‘.« _
H l“ \ ‘ . c" \ C
1'” . i ' = <"‘“-T‘ an “5'": , 39' ‘ W
I, ~ , v v R \\" '
I”: $ “mu,” 6’ it, u‘ t,
-8 ’— lllll:'"“lllllllliil‘l'lo I'M” . 0‘ _
-.. I"
-10 L 1 1 1 l
-15 -10 -5 0 5
Y-axns (mm)

Figure 67: z-y location of mandibular coordinate system
for horse #7 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

128

Hay

 

l - f T l r 5 I
4 r m Opering Phase a
::;,. — Closing Phase
M?‘
E ”I. " | a“.
E 0 ‘ ‘ 3’ 2. 1, 31mm”... \‘ ﬂ. '9'". _‘
V 4 .’ * pr 3%‘ " “‘2
P. « “‘e 7 \ .
m . A ' ' "\“ ‘ .‘
.g -2 __ . . l P a! x. a: .J
I
N -4 — —
-5 _ _

 

 

 

 

 

 

 

 

 

Z-axis (mm)

 

 

 

 

 

 

 

 

 

 

- 6 -14 -12 E -a ‘ 3 -4 é
X-axis (mm)

Figure 68: z-x location of mandibular coordinate system
for horse #7 chewing on the right
Solid line = Trial 1
Dashed line '—" Trial 2
Hatched line = Trial 3

 

 

 

 

 

 

 

 

 

 

 

 

I l 7 I I I
10 _ - Opening Phase
— Closing Phase
A 5 >—
E
E o —
V
.g -5 l—
,‘< -10 ~
-15 _
-20 1 L 1 4 1 1 1 1 1
-50 -40 -30 -20 -10 0 10 20 30 40
Y-axis (mm)
Pellets
T I I I
~*- Opel'ing Phase
— Closing Phase
A -5 ~
E
E,
.‘é -10 _
>'<
-15 _

 

 

 

Y-axis (mm)

10 15

Figure 69: x-y location of mandibular coordinate system

for horse #7 chewing on the right
Solid line = Trial 1
Dashed line = Trial 2
Hatched line = Trial 3

130

 

 

 

 

 

Appendix C:

Mandibular Euler angles for all horses

131

Pitch Angle (Deg)

Roll Angle (Deg)

O
#—

Yaw Angle (Deg)

6:

.5

 

 

m Opening Phase
— Closing Phase

 

 

N
1

 

O
1

 

 

 

 

O
0‘
O
A
O
O
.1.
(D
O
N
O
O
N
U"
0

 

w

 

 

 

N
l

 

 

_I
T

 

 

 

O
U‘
0
.3
OF—
C
—L
ml-
0
N
o.—
O
N
(D
O

 

 

ON

 

 

 

 

i
h.
T

 

 

 

l l
100 150 200 250
Frame Number

0
UI
0

Figure 70: Euler angles for horse #1
while chewing hay on the right

132

 

A

 

N

O

Pitch Angle (Deg)

 

N

  
 
 

l 1% I

at.» Opening Phase

-I(ﬂo§nthase
f

 

 

 

 

 

 

(a)
O

l

l 1 l
40 60 80 1 00 1 20 140 160 1 80

 

N

Roll Angle (Deg)

O

 

I T

 

I l
«W Opening Phase
’a“a III<ﬂoﬂngFMMse

 

 

  

~_. 1“ . , .h ‘
‘ V v.
‘H’ H ‘
* ,
‘ . , w
’M-
1

 

J

 

M
O

L

160 180

~A\\,r~/"“’ﬁ“.’\/~’\\/F;wow~/“T\af\\Jpv\r‘ 4
L L l l
60 120 140

40 80 100

 

O

N

Yaw Angle (Deg)

 

&

I T I j I I I

m Opening Phase

 

 

 

  

 

 

 

O

— Closing Phase
L l l L l l l—
40 60 80 100 120 140 160 180

Frame Number

Figure 71: Euler angles for horse #1
while chewing pellets on the right

133

 

 

#0)

 

 

 

 

 

 

 

 

Pitch Angle (Deg)
ar'o o N

 

ON-b

Roll Angle (Deg)

 

 

 

 

 

at

T T T T ﬂ T
,4 i we Opening Phase
‘35: 2 9‘ — Closing Phase —
i w J
M4", / if V \
a
1 l 1 l l l l L
00 200 300 400 500 600 700 800 900 1000
T T T T T T I T
M Opening Phase
f — Closing Phase
. I 3“ l :32." '» «5r
’Vwbﬂm "212'. ‘5" «I! 7 -
V4": M/ 1
l l 1 l l l l l
00 200 300 400 500 600 700 800 900 1000

 

.3
U" o

O

 

T T T T T T T T
-- Opering Phase
— Closing Phase

”Whack EWMWA

 

 

 

 

 

 

 

l
41.71

Yaw Angle (Deg)

1 l l J l l
200 300 400 500 600 700 800 900 1000
Frame Number

Figure 72: Euler angles for horse #2
while chewing hay on the left

134

 

 

ON‘O)

 

 

 

 

 

 

 

Pitch Angle (Deg)

 

O-‘N

I
A

Roll Angle (Deg)

 

 

 

 

 

 

 

4”

 

&

N

O

 

 

 

 

 

 

 

 

‘8‘”

Yaw Angle (Deg)

l l
200 250 300 , 350 400 450
Frame Number

Figure 73: Euler angles for horse #2
while chewing pellets on the left

135

 

O N A
T

Pitch Angle (Deg)

 

 

A
o

 

I I 1
U N A o
I I I

Roll Angle (Deg)

 

 

A
o

 

A
T

Yaw Angle (Deg)

 

 

lb
0

 

Frame Number

Figure 74: Euler angles for horse #3
while chewing hay on the leﬁ

136

 

 

 

 

 

 

 

 

 

 

 

 

 

 

N

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A
O) T T T T T I
8 .. - Opening Phase
V
.2 0‘
a
E -2 I
.C
O
E .4 1 1 1 1 1 1
100 150 200 250 300 350 400
A 0 r T T 1 r 1
3 m- Opening Phase
Q_1 _ ‘ i . ”.3 ., 1m — Closing Phase
o 2. '45., 3., '- F u
— . _, ~ \
32» V T ' d
E
(I -3 1 4 l L A 1
100 150 200 250 300 350 400
E 4
v l—
2 2
U)
C
< 0 a“, ..
>. -2 l 1 1 1 ‘ 1 L
100 150 200 250 300 350 400

Frame Number

Figure 75: Euler angles for horse #3
while chewing pellets on the left

137

450

 

N

 

Pitch Angle (Deg)

 

 

 

 

 

 

 

008M

 

N
T

A
T

Roll Angle (Deg)

 

 

 

 

 

 

 

80

240

 

O N A
I

I
N
I

 

Yaw Angle (Deg)
1.

 

 

 

 

 

 

 

 

8

 

 

J l
140 160
Frame Number

Figure 76: Euler angles for horse #4
while chewing hay on the leﬁ

138

 

N

 

Pitch Angle (Deg)
.3 o ..

 

 

 

 

 

 

 

8”

N

 

l
160 180

 

.5
$01100!

Roll Angle (Deg)

O

 

 

   

 

 

 

 

 

”8'01

 

O

N

 

Yaw Angle (Deg)

 

 

 

 

 

 

 

Bin

- Opering Phase
— Closing Phase
40
T
40 60 80 100 120 140 160 180

Frame Number

Figure 7 7 : Euler angles for horse #4
while chewing pellets on the leﬁ

139

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A10 T I T T T I
g 1m- Opening Phase
v — Closing Phase
in 5“ 9"

o ..
S T
o
E _5 1 1 1 1 1 1 1

0 50 100 150 200 250 300 350 400
A 3 I
52—
G
'5: 1~
:
E 01- 2‘
m _1 1 1 1 1 1 1 1

0 50 100 150 200 250 300 350 400
a 2 T T T T T I
8 -- Opening Phase
v 0" — ClosingPhase '1
2 ‘2 “‘
oa-Z— ~
§-4 h .1
>_ '6 1 1 1 1 1 J 1

0 50 100 150 200 250 300 350 400

Frame Number

Figure 78: Euler angles for horse #5
while chewing hay on the right

140

 

 

O N A O)
T

 

Pitch Angle (Deg)

1
N

 

 

 

 

 

 

O

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

50 100 150 200 250 300 350
A3 I T F I 1 r
§ m Opening Phase
V2 — Closing Phase
0 WQ
3 1 a...
1:1_
< _ “a,
g o J L L l J L l
0 50 100 150 200 250 300 350
29 2 T
Q
2 °"
a
E -2-
>- -4 *

 

O

100 150 200 250
Frame Number

Figure 79: Euler angles for horse #5
while chewing pellets on the right

141

 

 

 

&

N
I

O
I

 

 

 

 

 

 

Pitch Angle (Deg)

r'o
c>

 

O N h
I

Roll Angle (Deg)

 

 

 

 

 

 

 

 

.&
c:

100 200 300 400 500 600 700

 

 

\/: \_/“"")‘ ?”‘=' — Cbgng‘pm”
J. vﬁw

T I l I 7

 

 

 

 

 

 

Yaw Angle (Deg)

l l l l
100 200 300 400 500 600 700
Frame Number

Figure 80: Euler angles for horse #6
while chewing hay on the right

142

 

Pitch Angle (Deg)
O N A m

 

N

 

 

 

 

 

 

(a)
O

 

N

Roll Angle (Dog)

0

 

 

 

 

 

 

 

 

M
O

 

O

N

Yaw Angle (Deg)

i

 

 

 

 

 

 

 

 

O

400
Frame Number

Figure 81: Euler angles for horse #6
while chewing pellets on the right

143

 

 

 

O N A O)
I

 

-- Opering Phase
— Closing Phase

 

 

 

 

 

Pitch Angle (Deg)

r'o
o

 

N

Roll Angle (Deg)

 

O
l

u
N
l

 

 

 

 

 

 

 

b
o

 

 

Yaw Angle (Deg)

O N J-
l

I
N
I

 

 

 

 

 

 

 

3
o

50 100 150 200 250 300 350
Frame Number

Figure 82: Euler angles for horse #7
while chewing hay on the right

144

 

O-‘NU

 

A

 

 

 

 

 

Pitch Angle (Deg)

O

T l T
5"- : :
3 l l l

100 200

l
300 400 500 600 700

 

.6
401°

0
.5
UI

 

Roll Angle (Deg)

I
N

 

  
 

 

 

 

 

0

j raw Opening Phase
1 ‘1 1“ 5‘31; — Closing Phase ~
~ - a. .- 1" ‘
L l, i
l l 1 1 l g
100 200 300 400 500 600 700
l l l T I If

 

ON‘

I
N

 

Yaw Angle (Deg)

r
b

 

 

 

 

 

.4 1 5.
‘1‘ i‘ )"U A _
‘1 , s
q
1 4 1 1 1 1

 

O

100 200 300 400 500 600 700
Frame Number

Figure 83: Euler angles for horse #7
while chewing pellets on the right

145

Bibliography

Baker G. and Easley J (1999) Equine Dentistry. W.B. Saunders Company Ltd. New
York. pp. 30-32

Becker E (1962) Cited by Dixon PM (2000) Equine dental disease Part 3: a long-term
study of 400 cases: disorders of wear, traumatic damage and idiopathic fractures,
tumors and miscellaneous disorders of the cheek teeth. Equine Veterinary Journal
Vol. 32, No. 1, pp. 9-18.

Brunner J (1941) Cited by Dixon PM (2000) Equine dental disease Part 3: a long-term
study of 400 cases: disorders of wear, traumatic damage and idiopathic fractures,
Mums and miscellaneous disorders of the cheek teeth. Equine Veterinary Journal
Vol. 32, No. 1, pp. 9-18.

Capozzo A, Gazzani F, and Macellari V (1988) Skin marker artifacts in gait analysis.
Proceedings of the 6th meeting European Society of Biomechanics. Butterworth,
London. p. C23

Chen J and Buckwater K (1992) Motion analysis of the mandibular condyle from
magnetic resonance images. Advances in Bioengineering Vol. 22, pp. 545-548.

Christiansen E, Thompson J, Hasso A, Hinshaw D, Moore R, Roberts D, and Kopp S
(1987) CT number characteristics of malpositioned TMJ menisci diagnosis with
CT number highlighting (blinkmode). Investigative Radiology Vol. 22, No. 4, pp.
315-321.

Collinson M (1994) Food processing and digestibility in horses (Equus caballus). BSc
dissertation, Monash University.

Dyce KM, Sack W0, and Wensing, CJG ( 1987) Textbook of Vetmw Anatomy. W.B.
Saunders Company Ltd. Philadelphia. pp. 61-65, 111-113.

Duncan P (1992) Horses and Grass: The nutritive ecology of Quids and their impact on
the earmargge. Springer-Verlag, New York.

Encyclopedia Britannica (2001) Britannica.com, Chicago, IL.

Fredricson I and Drevemo S (1971) A new method of investigating equine locomotion.
Equine Veterinary Journal Vol. 3, No. 4, pp. 137-140.

Gallo LM, Fushima K, and Palla S (2000) Mandibular helical axis pathway during
mastication. Journal of Dental Research Vol. 79, No. 8, pp. 1566-1572.

146

Gobel F and Duffner K (1954) Cited by Dixon PM (2000) Equine dental disease Part 3: a
long-term study of 400 cases: disorders of wear, traumatic damage and idiopathic
fractures, tumors and miscellaneous disorders of the cheek teeth. Equine
Veterinary Journal Vol. 32, No. I, pp. 9-18.

Grood ES and Suntay WJ (1983) A joint coordinate system for the clinical description of
three simensional motions: application to the knee. Journal of Biomechanical
Engineering Vol. 105, pp. 136-144.

Haug EJ (1989) Computer-Aided Kinemtics and Dynamics of Mechanical Systems.
Volume I: Basic Methods. Allyn and Bacon. Boston. pp.305-328

Jeffrey D (1986) Equine Dentistry Mam]. VOIUQC II. Leatherwork & Horse Tack &
World Wind Equine Dental Supply Company. Waverly, NE. p. 1.

J oest E (1970) H_andbuch der Speziellen Pathologischen An_atomie der Haustiere, Em
V, Digestionsapparat, 1. Teil. Verlag Paul Parey. Berlin. ppl3 1-132

Johnson TJ (2000) Advanced Equine Dentistry. Recorder #114.

Kadaba MP, Ramakrishnan HK, and Wooten ME (1990) Measurement of lower
extremity kinematics during level walking. Journal of Orthopaedic Research Vol.
8, No. 3, pp. 383- 392.

Koolstra JH and van Eijden TMGJ (1992) Application and validation of a three-
dimensional mathematical model of the human masticatory system in vivo.
Journal of Biomechanics Vol. 25, No. 2, pp. 175-187.

Leue G (1941) Cited by Becker, E (1962) Zahne. In: Handbuch der Sncziellen
P‘athologischen Anatomic der Haustiere, Eds: J Dobberstein, G. Pallaske and H.
Stunzi, Band V, 3rd edn, Verlag Paul Parey, Berlin. pp.l31-132.

Leue G (1941) Cited by Dixon PM (2000) Equine dental disease Part 3: a long-term
study of 400 cases: disorders of wear, traumatic damage and idiopathic fractures,
tumors and miscellaneous disorders of the cheek teeth. Equine Veterinary Journal
Vol. 32, No. 1, pp. 9-18.

Ostry D, Vatikiotis-Bateson E, and Gribble P (1997) An examination of the degrees of
freedom of human jaw motion in speech and mastication. Journal of Speech,
Language and Hearing Research Vol. 40, pp. 1341-1351.

Patterson LJ, Shappell K, and Hurtig MB (1989) Mandibular condylectomy in a horse.

Journal of American Veterinary Medical Association Vol. 195, No. 1, pp. 101-
102.

147

Paz M, Carter L, Westesson P, Katzberg R, Tallents R, Subteiny D, and Goldin B (1990)
CT dentistry of the TMJ disk: Correlation with histological observations of
hyalinization, metaplastic cartilage, and calciﬁcation in autopsy specimens.
American Journal of Orthodontics Dentofacial Orthopaedics Vol. 98, No. 4, pp.
354-357.

Plesh 0, Bishop B, and McCall WD (1993) Kinematics of jaw movements during
chewing at different frequencies. Journal of Biomechanics Vol. 26, No. 8, pp.
243-250.

Ramakrishnan HK and Kadaba MP. (1991) On the estimation of joint kinematics during
gait. Journal of Biomechanics Vol. 24, No. 10, pp. 969-977.

Raustia AM and Pyhtinen J (1990) Morphology of the condyles and mandibular fossa as
seen by computed tomography. The Journal of Prosthetic Dentistry Vol. 63, No.
I, pp. 77-82.

Reinschmidt C, van den Bogert AJ, Nigg BM, Lundberg A, and Murphy N (1997).
Effect of skin movement on the analysis of skeletal knee joint motion during
running. Journal of Biomechanics Vol. 30, No. 7, pp.729-732.

Rosenstein DS, Bullock MF, Ocello PJ, and Clayton HM (2001). Arthrocentesis of the
temporomandibular joint in adult horses. American Journal of Veterinary
Research Vol. 62, No. 5, pp. 729-733.

Salomon JA, Waysenson BD (1979) Computer-monitored radionuclide tracking of three-
dimensional mandibular movements. Part 1: Theoretical approach. Journal of
Prosthetic Dentistry Vol. 41, No. 3, pp. 340-344.

Sisson S and Grossman JD (1975) The Anatomy of Domestic Animals, Volume I W.B.
Saunders Company. Philadelphia. pp. 318-342, 384-386.

Soderkvist I and Wedin P (1993) Determining the movements of the skeleton using well-
conﬁgured markers. Journal of Biomechanics Vol. 26, No. 12, pp. 1473-1477.

Triola MF (1998) Elementary Statistics Seventh Edition. Addison-Wesley. New York.
pp. 288-308.

Visscher CM, Huddleston Slater JJR, Lobbezoo F, and Naeje M (2000) Kinematice of the
human mandible for different head postures. Journal of Oral Rehabilitation Vol.
27, pp. 299-305.

Warmerdam EPL, Klein WR, and van Herpen BPJM (1997) Infectious

temporomandibular joint disease in the horse: computed tomographic diagnosis
and treatment of two cases. Veterinary Record Vol. 141, pp. 172-174.

148

Woltring HJ (1986) A FORTRAN package for generalized, cross-validatory spline
smoothing and differentiation. Advances in Engineering Software Vol. 8, No. 2,
pp. 104-113.

Weller R, Cauvin ER, Bowen IM, and May SA (1999) Comparison of radiography,
scintigraphy and ultrasonography in the diagnosis of a case of temporomandibular
joint arthropathy in a horse. Veterinary Record Vol. 144, pp. 377-379.

Yatabe M, Zwijnengurg A, Megens CCEJ, Naeije M (1997) Movements of the
mandibular condyle kinematic center during jaw opening and closing. Journal of
Dental Research Vol. 76, No. 2, pp. 714-719.

Zhang X, Ashton-Miller JA, and Stohler CS (1995) Three-dimensional unilateral method

for the bilateral measurement of condylar movements. Journal of Biomechanics
Vol. 28, No. 8, pp. 1007-1011.

149