The effects of stress and malocclusion on masseter EMG activity

MISSING IMAGE

Material Information

Title:
The effects of stress and malocclusion on masseter EMG activity
Physical Description:
x, 99 leaves : ; 29 cm.
Language:
English
Creator:
Bichajian, Charles, 1954-
Publication Date:

Subjects

Subjects / Keywords:
Stress, Psychological -- complications   ( mesh )
Malocclusion   ( mesh )
Clinical and Health Psychology thesis Ph.D   ( mesh )
Dissertations, Academic -- Clinical and Health Psychology -- UF   ( mesh )
Genre:
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1984.
Bibliography:
Bibliography: leaves 92-98.
Statement of Responsibility:
by Charles Bichajian.
General Note:
Typescript.
General Note:
Vita.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 000484435
oclc - 14155402
notis - ACQ2313
System ID:
AA00009144:00001


This item is only available as the following downloads:


Full Text












THE EFFECTS OF STRESS AND MALOCCLUSION
ON MASSETER EMG ACTIVITY









By

CHARLES BICHAJIAN


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY




UNIVERSITY OF FLORIDA


1984















ACKNOWLEDGMENTS


I would like to express my very special thanks to my chairman,

Dr. F. Dudley McGlynn, and his wife Brenda for their unfailing support

and guidance during the past seven years. Also due thanks are the

other members of my supervisory committee, Dr. Hugh C. Davis, Dr.

Russell M. Bauer, Dr. Wallace L. Mealiea, and Dr. Parker E. Mahan, for

their support and advice over the years.

I owe a special debt of gratitude to Dr. Harry Lundeen, not

only for making this project possible, but also for making it fun at

times. I wish to acknowledge the eight subjects, Lynn, Michelle, Rae,

Debbie, Joyce, Shirley, Joanne, and Patty, for their patience and

fearlessness. Several people provided technical assistance and are

due a vote of thanks-Jeff Cassisi, Barry Nicholas, Ed Neu, and Sofia

Kohli.

I am particularly indebted to my father, Dr. John Bichajian,

for his moral and financial support without which this project would

never have been undertaken. Finally, it is a pleasure to express my

appreciation to Lynn, Lester, Ernie, Manoli, Sue, Carol, Rade, and Chris

for their encouragement and advice.

















TABLE CONTENTS


ACKNOWLEDGMENTS . . .

LIST OF TABLES . . .

ABSTRACT . . . .


CHAPTER


ONE INTRODUCTION . . .

The Masticatory System . .
Functional and Nonfunctional Oral-Motor Behaviors .


Bruxism


Theories of Bruxism . ..
Local/Mechanical Theories .
Occlusion, malocclusion, and
occlusal interference .
Occlusal disharmony theory .
Epidemiological/correlational
studies . .
Experimental/quasi-experimental
studies . .
Evaluation of the literature .
Psychological Theories . .
Psychoanalytical/personality theories
Psychophysiological theories .


Stress .


Stress-related theories of bruxism
Correlational/naturalistic studies
Experimental/quasi-experimental
studies . .
Evaluation of the literature .
Interactive Theories . .
Empirical Status . .
Rationale of Present Experiment .

TWO METHOD . . .

Subjects . . .
Experimenters . . .


S 1
. 1
. 3


. . . 4


7

8
9



. 11
. 14
. 6
. 7


. 9

. 10

. 11
. 14
. 15
. 17
. 18


. 22
S. 25
S. 26
S. 28
S. 28

. 31


Page

. i


. .











CHAPTER Page

Apparatus . . 33
Electromyograph . 33
Electrodermograph . .. 33
Placebo and Maloccluding Interferences ... 33
Neutral and Stressful Films. . 35
Anxiety Differential . .. 36
Pain and Irritation Questionnaire .. 36
Procedure .... . 37

THREE RESULTS . .. . 40

Data Concerning Experimental Validity ... 40
General Analysis Strategy .. .. 41
Skin Conductance Data Analyses ........ 43
Anxiety Differential Data Analysis ...... 47
Laboratory and Clinical Examinations of
the Splints ...... . 47
Pain and Irritation Data Analysis ...... .. 48
Summary of Data Concerning Experimental
Validity .... .. . 49
Data Concerning the Experimental Manipulations 50
General Analysis Strategy . 50
EMG Data Analysis ...... . 51

FOUR DISCUSSION .... . 57

Data Concerning Experimental Validity . 57
Validity of the Stress Manipulation .. 57
Validity of the Occlusal Disharmony
Manipulation . 58
Future Research from a Procedural
Perspective . . 60
Data Concerning Experimental Manipulations .. 63
Effects of Stress Manipulation .. 63
Effects of Splint Manipulation . 64
Movie Content x Side of Recordingx Recording
Interval .... . 67
Future Research from a Substantive
Perspective . 67

APPENDIX

A DESIGN OF OCCLUSAL INTERFERENCE AND PLACEBO SPLINT 73

B PAIN AND IRRITATION QUESTIONNAIRE ... ... ... ... 74

C TESTING ORDER FOR SUBJECTS . 75

D ADDITIONAL DATA TABLES ...... . 77











Page

REFERENCES . ... . 92

BIOGRAPHICAL SKETCH . .... ..... .99















LIST OF TABLES


Table

3-1 Means, standard deviations, r values, and F
statistics from B1 and B2 regression analyses,
for SCL (in imhos), EMGI, and EMGC (in pvs),
grouped by session . .

3-2 Means and standard deviations for SCL change
and raw scores (in lmhos) and total number of
SCRs grouped by four movies . .

3-3 Means and standard deviations for raw B1 SCL
(in pmhos) and total number of B1 SCRs grouped
by session . . .


Page


44


3-4 Means and standard deviations for self-reported
anxiety based upon the Anxiety Differential,
grouped by four movies . .... 46

3-5 The summed total of self-report responses based
upon the pain and irritation questionnaire,
grouped by response type and splint condition .. 46

3-6 EMG change score summary table for 2x2 x 2 x 9
(splints movies x sides x intervals) ANOVA with
repeated measures, using condition subject
interaction as error term. . 53

3-7 Means and standard deviations for EMG change
scores for the significant movies sides intervals
interaction (in pvs) . . 55

D-1 Session 1 means and standard deviations for B1 and
B2, from SCL (in ymhos), EMGI, and EMGC (in pvs)
recordings for each of the nine intervals averaged
over the 8 subjects . ... .77

D-2 Session 2 means and standard deviations for B1
and B2, from SCL (in pmhos), EMGI, and EMGC
(in pvs) recordings for each of the nine intervals
averaged over the 8 subjects . .... .78











Table Page

D-3 Means and standard deviations for B1 computed
over the last four intervals from SCL (in
imhos), EMGI, and EMGC (in lvs) recordings
for each of the 8 subjects, grouped by session
(SCL) or by splint condition (EMG) . .. 79

D-4 Means and standard deviations computed over
nine intervals for SCL change scores from baseline
for each of the 8 subjects, grouped by four
movies (in ipmhos) . . ... .80

0-5 Means and standard deviations computed over nine
intervals for SCL raw scores for each of the
8 subjects, grouped by four movies (in imhos) .. 81

D-6 The number of SCRs totaled over nine intervals
for each of the 8 subjects, grouped by session
(Bl) or by movies . . ... .82

D-7 The level of self-reported anxiety based upon
the Anxiety Differential for each of the 8 sub-
jects, grouped by four movies . .... .83

D-8 The self-report ratings of pain and local irrita-
tion based upon the pain and irritation ques-
tionnaire, for each of the 8 subjects, grouped
by splint condition . .... .84

D-9 Means and standard deviations for EMGI change
scores from baseline grouped by movie and
splint conditions (in pvs) . .... .85

D-10 Means and standard deviations for EMGC change
scores from baseline, grouped by movie and splint
conditions (in yvs) . ... .85

D-11 Means and standard deviations for EMGI raw
scores grouped by movie and splint conditions
(in Pvs) . . ... .86

D-12 Means and standard deviations for EMGC raw scores
grouped by movie and splint conditions (in yvs) .... 86

D-13 Means and standard deviations for EMG change
scores grouped by movie and splint condition
(in ivs) . . ... ... .. .87

D-14 Means and standard deviations for EMG raw scores
grouped by movie and splint conditions (in lvs) ..... 87











Table Page

0-15 Means and standard deviations computed over nine
intervals for EMGI change scores from baseline
grouped by condition and subject (in pvs) ...... .88

D-16 Means and standard deviations computed over
nine intervals for EMGC change scores from
baseline grouped by condition and subject (in
Jvs) . . ... .89

D-17 Means and standard deviations computed over nine
intervals for EMGI raw data grouped by condition
and subject (in lvs) . ... .90

D-18 Means and standard deviations computed over
nine intervals for EMGC raw data grouped by condi-
tion and subject (in yvs) . .... .91


viii















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy



THE EFFECTS OF STRESS AND MALOCCLUSION
ON MASSETER EMG ACTIVITY

By

Charles Bichajian

December 1984

Chairman: F. Dudley McGlynn
Major Department: Clinical Psychology

Hyperactivity in the muscles of mastication leads to abnormal

wear and damage to the teeth, to hypertrophy of the masticatory muscles,

and to pain in several regions of the face. Recently, multifactorial

theories have posited that mandibular muscle hyperactivity mirrors the

interacting effects of psychological stress and malocclusion. This

study experimentally examined the unilateral and interacting effects of

psychological stress and malocclusion on bilateral masseter EMG

activity.

According to a completely counterbalanced design, 8 females

presenting with no recent history or clinical signs of oral-motor dis-

orders were twice subjected to horrific and neutral movie segments, once

after having worn an occlusal interference splint and once after having

worn a non-interference (placebo) splint for approximately 19 hr. During

both experimental sessions bilateral masseteric EMG levels were recorded











as were skin conductance levels and responses. After the session,

semantic differential ratings were acquired. A 2x2x2x9 (type of

splint x movie content x side of recording x interval of recording)

ANOVA with repeated measures on all factors was conducted within masseter

EMG change from baseline data and within baseline-independent EMG raw

scores. Both ANOVAs yielded significant main effects for movie content,

side of recording, and intervals of recording along with two significant

interactions involving these variables. The horrific movie segments,

in general, produced greater masticatory muscle activity than did the

neutral movie segments. The side contralateral to both splints, in

general, showed greater muscle activity than did the side ipsilateral

to the splints. In general, the greatest muscle activity occurred

towards the end of the movie segments. The interaction of these

factors was such that movie content and side of recording combined to

influence EMG values for some but not all recording intervals. The

electrodermal and semantic differential data showed the horrific movie

to be stressful. The significant effect for side of recording mirrored

the result of irritating dental conditions. Hence the interaction of

movie content and side of recording manifested for the first time an

interaction between psychological stress and local dental conditions.

The meanings and limitations of the data are discussed along with

directions for future research.















CHAPTER ONE
INTRODUCTION

Chronic and/or episodic hyperactivity in the muscles of masti-

cation (i.e., bruxing) produces a variety of oral health problems.

Health professionals concerned with the oral cavity are, therefore,

interested in how individuals come to be bruxers. One view of the

problem is that bruxing and related muscular hyperactivity reflect psy-

chobiologicstress. A second view of the problem is that bruxing/muscular

hyperactivity mirrors occlusal imbalance within the masticatory system.

A third view is that bruxing/muscular hyperactivity results from the

interaction of both psychobiologic stress and occlusal imbalance within

the masticatory system. In the'experiment reported here, attempts were

made to affect subjects' mandibular muscle activity by manipulating the

variable of stress, by manipulating the variable of occlusal balance,

and by permitting these two variables to interact. By way of intro-

ducing the experiment, the following narrative describes the masticatory

system, its functional and nonfunctional behaviors, and the character-

istics, diagnoses, and concepts associated with bruxism. In addition,

major theories of bruxism are reviewed along with the currently avail-

able literature bearing on them.


The Masticatory System

Human oral-motor behavior is controlled by the masticatory

system which is a functional unit composed of the teeth and their










surrounding and supporting structures, the maxillae (upper jawbones),

the mandible (lower jawbone), the temporomandibular joints, the lips,

tongue, and masticatory muscles, and the vascular and nervous systems

for these tissues (Ramfjord & Ash, 1983). The muscles constitute the

active parts of this system while the ligaments and bony elements are

considered to be the passive parts. The muscles of the tongue are

divided into right and left paired groups made up of extrinsic and

intrinsic muscles (Kimber, Gray, Stackpole, & Leavell, 1961). The pri-

mary extrinsic muscles of the tongue are the genioglossus and stylo-

glossus which originate from the mandible and the temporal bone,

respectively. The genioglossus muscle functions to retract, protrude,

and depress the tongue. The primary muscles of mastication are the

temporal, masseter, internal (medial) pterygoid, and external (lateral)

pterygoid muscles. The accessory muscles of mastication include the

suprahyoid group (digrastic, mylohyoid, geniohyoid, and stylohyoid

muscles), infrahyoid group, and platysma muscle (Ermshar, 1982).

The masseter muscle is a thick quadrilateral muscle composed

of a deep belly and a superficial belly. The muscle arises from the

zygomatic process and surrounding parts of the maxilla and is inserted

into the angle and lateral surface of the ramus of the mandible (Kimber

et al., 1961). The masseter muscles function primarily during mandibu-

lar elevation (jaw closing) and protrusion (Ermshar, 1982) although

they are also active during extreme lateral movements of the mandible.











Functional and Nonfunctional Oral-Motor Behaviors

The major human oral functions include speech, mastication,

swallowing, coughing, and gagging (Sessle, 1979). Integrated activi-

ties of the masticatory system other than talking, chewing, breathing,

and swallowing are labeled nonfunctional or parafunctional (Ramfjord &

Ash, 1983). The distinction between functional and nonfunctional oral-

motor behavior has been made in two related ways. First, functional

activities are those which represent the adaptive end-result of evolu-

tion. It is believed that the mammalian masticatory system evolved

from gill arches that in vertebrate filter feeders performed simul-

taneously the activities of feeding and breathing. Hence, chewing,

breathing, and swallowing are functional oral-motor behaviors in an

evolutionary sense. Secondly, and more importantly, functional activi-

ties are those in which tactile control and reflex coordination serve

automatically as mechanisms protecting the integrity of the masticatory

system. There are no protective mechanisms for nonfunctional oral-

motor behaviors, however, and physiologic tolerance levels often are

exceeded (cf. Posselt, 1968).

Tishler (1928) was among the first to note the uniformly unadap-

tive consequences of recurring behaviors he referred to as "occlusal

habit neuroses." Among these parafunctional behaviors are biting

foreign objects, lip/cheek biting, tongue thrusting, and hand-to-mouth

behaviors such as thumbsucking. Biting on common foreign objects such

as pencils, bobby pins, eye glasses, and sewing thread can damage the

masticatory system by destroying tooth enamal and producing malocclusion.











Lip, tongue, and cheek biting can damage soft oral tissues and can also

contribute to malocclusion via awkwardly positioning the mandible and,

in turn, changing wear patterns in occlusal contacts (Ramfjord & Ash,

1983). Both dentists and psychologists have been interested in finger-

sucking and thumbsucking. Hence a large literature addresses these

parafunctional behaviors.


Bruxism

Nonfunctional or parafunctional grinding, gnashing, and clenching

of teeth within and beyond the functional range of occlusion is an oral-

motor disorder termed bruxism. The term bruxism comes from the French

word "la bruxomanie,"which was first used by Marie and Pietkiewicz in

1907. In addition to the word bruxism, other terms such as "neuralgia

traumatica," "Karolyi effect," "occlusal habit neurosis," and "para-

function" have been used over the years to designated nonfunctional

teeth grinding (Ramfjord & Ash, 1983). Bruxing may occur primarily

at night (noctural bruxism) or primarily during the day (diurnal

bruxism). The etiologies of diurnal and nocturnal bruxing probably

differ. Assessment and treatment approaches differ as well.

The term "centric bruxism" refers to habitual clenching of the

teeth in and around the intercuspal position. It derives from the term

"power centric" that refers to the position of the mandible from which

a person can bite the hardest. "Eccentric bruxism" refers to grinding

and gnashing. Clenching primarily involves the masseter and temporal

muscles, while grinding and gnashing primarily involve the lateral and

medial pterygoid muscles (Boos, 1952; Dubner, Sessle, & Storey, 1978).










Bite force is an important quantitative dimension in all types

of bruxist activity. Bite forces during mastication have been estimated

to be from 12 Ib to 60 Ib (Gibbs, Mahan, Lundeen, Brennan, Walsh,

Sinkewiz, & Ginsberg, 1981). During bruxing, bite forces of 200 to

300 Ib are observed. The maximal purposeful biting forces in non-

bruxist subjects are in the range of 55 to 280 lb, whereas deliberate

bite forces in excess of 500 lb have been recorded for bruxist sub-

jects (C. H. Gibbs, personal communication, October 15, 1984).

Methodologically heterogeneous studies have prompted disparate

estimates of the incidence of bruxism in the adult population, ranging

from 15% to 88% (Mahan, 1981). A number of investigators (e.g., Molin

& Levi, 1966) have found sex differences in the incidence of bruxism,

with the number of women significantly outweighing the number of men.

However, these differences have occurred among people reporting for

treatment and might reflect sex differences in help seeking, not bruxing.

When objective measurements are made, males and females show signs and

symptoms of bruxism with the same frequency (Rugh, 1978).

Glaros and Rao (1977), among others, have described the sympto-

matic effects of bruxing. Among these effects are abnormal wear to

the teeth and damage to surrounding and supporting structures. Struc-

tural damage of this type includes recession and inflammation of the

gums and resorption of the alveolar bone. Bruxism has been implicated

also in hypertrophy of the masticatory muscles, in muscle and tooth

sensitivity, and in headaches.

Bruxism, in combination with some other forms of abnormal muscle

activity, is of contemporary interest due to the role it seems to play










in chronic facial pain syndromes, particularly the myofascial pain

dysfunction (MPD) syndrome. The most common characteristic of the MPD

syndrome is pain of unilateral origin, typically described as a "dull

ache" felt in the preauricular area, that may radiate to the angle of

the mandible, to the temporal area, or to the lateral cervical region

(Laskin, 1969). The major experiment linking masticatory muscle

hyperactivity to facial pain was conducted by Christensen (e.g., 1971).

Related work has been reported by Scott and Lundeen (1980). Christensen

had 9 healthy human subjects perform right-sided tooth grinding in the

supine position for 30 min. Eight of the 9 subjects reported mild to

moderate deep facial pain occurring an average of 2 hr after grinding

was begun. Scott and Lundeen had 15 subjects vigorously thrust their

mandible forward for 5 min. Self-report pain and incisal opening

measures from the 15 experimental subjects were compared with cor-

responding measures among 15 control subjects who were asked to hold a

tongue blade loosely between their teeth for 5 min. Scott and Lundeen

found that vigorous protrusion of the mandible produced ratings of

moderate to severe muscle pain that were significantly greater than

were ratings among the control subjects. Additionally, they found that

the pain was similar to MPD pain with respect to anatomical location,

quality, and intensity.


Theories of Bruxism

Many health-care professionals from diverse disciplines have

been involved in developing explanatory models/theories pertaining

to bruxist behavior. Mahan (1981) found in the literature numerous











theories of bruxism, some of which are occlusal interference, brain

damage, sympathetic nervous system overactivity, drug use (especially

amphetamines), abnormal sleep states, physical pain, and heightened

emotional states. Attempts have been made to arrange these diverse

theories into cohesive classes. Glaros and Rao (1977) adapted the

classification system for bruxist theories first developed by Nadler

(1957). The three categories of local/mechanical, psychological, and

systemic/neurophysiological were presented as being parsimonious and

heuristic although not mutually exclusive. The classification system

used by McGlynn, Cassisi, and Diamond (in press) replaced Glaros and

Rao's third category (systemic/neurophysiological) with a category they

labeled as "interactive." Although this approach tends to downplay

the role of systemic factors (which are undoubtedly important) this new

category scheme focuses attention on the complex nature of bruxing.

Over the past 5 years, it has become increasingly clear that, as

McGlynn et al. argue, bruxing behavior is a result of multiple, inter-

acting causes within various etiological domains. For the present

purpose the theoretical categories of local/mechanical, psychological,

and interactive are the most pertinent.


Local/Mechanical Theories

Karolyi (1901) was probably the first professional to recognize

the relationship between local oral conditions and bruxism. Since

1901, there have been numerous theories attempting to relate features











of the dentition to abnormal masticatory muscle activity. Theories

have posited that bruxism results from rough cusp ends (Tishler, 1928),

from missing, elongated, and poorly restored teeth (Frohman, 1931), and

from calculus and excessive cuspal inclination (Leof, 1944). The

various local/mechanical theories have been reformulated over the

years and have shifted toward some type of occlusal disharmony as the

major basis of bruxism.


Occlusion, malocclusion, and occlusal interference

The concept of occlusion has been variously defined in terms

of static relationships, in terms of dynamic (moving) relationships,

and in terms of functional adequacy within the stomatognathic system.

Both static and dynamic definitions of occlusion can take as departure

points either the structures of the temporomandibular joint (TMJ) or

tooth-to-tooth relationships. The TMJ structures include the condyles,

the articular discs, and the glenoid fossae. The most common TMJ-

determined occlusal position is that of centric relation (CR). Crawford

(1984) defines CR as an orthopedic position in which "both condyles

are in the most superior positions in the glenoid fossae with the

articular discs interposed irrespective of tooth contacts" (p. 40).

The most common tooth-determined occlusal position is that of centric

occlusion (CO). Centric occlusion is the position of the mandible

during maximum intercuspation.

For the average healthy human, the positions of CR and CO do

not coincide. If the maxillary and mandibular teeth are touching and

there is an unrestricted glide between CR and CO, then theoretically no











neuromuscular adaption is required. This state of affairs is known as

"ideal occlusion" and it forms the conceptual basis for defining

"normal occlusion." According to Ramfjord and Ash (1983), normal

occlusion is defined by a range of anatomically acceptable deviations

from ideal occlusion as well as by the absence of functional dis-

turbances. In turn, malocclusion is defined by a range of unacceptable

deviations from ideal occlusion as well as by the presence of dysfunc-

tional relationships within the masticatory system.

If the maxillary and mandibular teeth are touching and there

are restrictions to smooth gliding between CR and CO, then "occlusal

interference" are said to exist. Three types of interference are

cited as most common: (a) unilateral tooth contact in CR with a

lateral slide on moving to CO, (b) tooth contacts on the nonworking

(balancing) side that prevent contact on the working side, and

(c) steep cuspal inclines on the working side that prevent smooth

laterotrusive excursions. (For a review of these and related concepts

see Carlsson and Droukas, 1984.)


Occlusal disharmony theory

Generally, the occusal disharmony theory of bruxism is a homeo-

static one in which an end state of occlusal harmony somehow motivates

the masticatory system to seek out and remove the occlusal interferen-

ces. The interference are used as bruxing contacts and ground with

abnormal force in order to restore balanced occlusion. Although many

dentists argue that any interference can lead to bruxing activity,











retruded contact position interference [(a) above] and balancing side

interference [(b) above] are cited most often in the literature.

There is a sizable literature examining bruxing and other oral-motor

disturbances in relation to these and other types of occlusal inter-

ferences. Masticatory EMG activity, mandibular postural activity,

biochemical activity, and various signs and symptoms of mandibular

dysfunction have all been used as dependent and/or covariate measures.

As a matter of convenience the following narrative is divided into two

categories: epidemiological/correlational studies and experimental/

quasi-experimental studies.

Epidemiological/correlational studies. Geering (1974) offered

a post hoc analysis of the pain histories and occlusal functioning of

282 patients. He found balancing side interference to be almost twice

as frequent in patients with pain and other TMJ symptoms as in patients

without symptoms. It should be noted, though, that 40% of the indi-

viduals with occlusal interference did not suffer from pain or other

clinical symptoms. Molin, Carlsson, Friling, and Hedegard (1976)

found that patients with mandibular dysfunction presented significantly

greater combinations of different occlusal interference than did

patients without mandibular dysfunction. In a similar study, Heloe,

Heiberg, and Krogstad (1980) performed occlusal examinations on 113

female MPD patients and 46 female non-MPD dental patients. The only

significant difference between the groups was a higher number of patients

with retruded contact position interference in the MPD group.

Using the clinical dysfunction index of Helkimo (1979), DeBoever

and Adriaens (1983) divided 135 TMJ pain patients into five subgroups











according to the severity of their symptoms. No significant relation-

ship was found between the severity of symptoms and the number of

patients with retruded contact position or working side interference.

The author did find a disproportionate number of subjects with balancing

side interference in the most severely symptomatic subgroup. Finally,

Thomson (1971) compared 100 TMJ pain patients with 100 controls and

found no significant differences between the two groups with regard

to the incidence of occlusal interference, clenching habits, or other

dental conditions.

Experimental/quasi-experimental studies. In an experimental

study, Bakke and Moller (1980) placed celluloid strips, 0.05, 0.10,

0.15, and 0.20 mm thick, unilaterally between the first molars of 4

subjects and compared the level of EMG activity under the different

strip conditions and during undisturbed occlusion. With the celluloid

prematurity in place, biting in the intercuspal position caused

assymetric EMG activity for both the temporal and masseter muscles.

As compared to recordings with undisturbed occlusion, EMG activity was

significantly higher ipsilaterally and significantly lower contra-

laterally. As the thickness of the strips increased, the mean EMG

voltage decreased on both sides in parallel.

Randow, Carlsson, Edlund, and Oberg (1976) placed a gold inlay

unilaterally in one of the mandibular first molars of 8 dental students

with normal occlusion. The subjects were instructed to bite maximally

in the retruded and intercuspal positions, both before and after inser-

tion of the interference. Overall, there was a slight decrease in










masseter and temporal EMG activity following insertion of the inlay

but, interestingly, coordinational disturbances were also noted.

These results were found both ipsilateral and contralateral to the

interference. Approximately 1 week following placement of the inter-

ference, a clinical examination revealed MPD symptoms in a number

of the subjects. Reported symptoms included pain, muscle and TMJ

tenderness to palpation, clicking, irregular movements during mandibu-

lar opening, and periodontal tenderness.

Riise and Sheikholeslam (1982) measured postural activity of

the masseter and anterior temporal muscles, via EMG, 1 hr, 48 hr,

and 1 week following insertion of a small, rounded, 0.50 mm high amal-

gam filling (interference) on the maxillary right first molar of 11

dental students with normal occlusion. The EMG measures were taken

while the subjects were alert, sitting upright with unsupported heads,

with eyes open, and with the instruction not to keep their teeth in

contact. No significant differences in postural activity, before and

1 hr following insertion of the interference, were found. Forty-eight

hour differences were significant for ipsilateral and contralateral

anterior temporal EMG measures. One week following insertion of the

interference, a significant difference was found only for the

contralateral anterior temporal EMG measure. Although masseter muscle

activity increased over the testing period, the differences were not

statistically significant. Interestingly, masseter muscle activity

on the contralateral side was consistently (but not statistically)

higher than on the ipsilateral side. In a similar study 13 years











earlier, DeBoever (1969) found no change, over an 8-day period, in

postural activity following insertion of a balancing side interference.

Using an ABA design, Rugh, Barghi, and Drago (1984) obtained

nocturnal masseter EMG recordings from 10 normally occluded nonbruxing

subjects before, during, and after insertion of a gold crown designed

to provide a 0.50 to 1.00 mm forward and lateral deflection from

centric relation. Five subjects showed statistically.significant

reductions in nocturnal masseter muscle activity during the 3-week

experimental period. Four subjects showed no significant change while

only 1 subject showed a significant increase in nocturnal bruxism when

the maloccluding crown was in place. Finally, 6 out of 10 subjects

were free of MPD symptoms throughout the study while 4 subjects showed

mild MPD symptoms.

In one of the better designed studies to date, Magnusson

and Enbom (1984) used an acid-etch technique to place balancing

side interference bilaterally on the maxillary first molars of 12

normally occluded, symptom-free female subjects. The application

of the interference were simulated, but not produced, in a similar

group of 12 subjects. The subjects in both the experimental and

control groups were given the same informed consent material and

treated exactly the same by a blind experimenter during follow-up

clinical examinations. One week following the application or simula-

tion of the interference a statistically significant increase from

baseline was seen in the clinical dysfunction index of the experimental

group. The dysfunction index among experimental subjects also was

significantly higher than the index among the control subjects. It











should be noted, though, that 3 of the 12 control subjects, showed

clinical signs of dysfunction. From these data, Magnusson and Enbom

conclude that "there is no simple and dramatic relationship between

interference and signs and symptoms of mandibular dysfunction" (p.

133).


Evaluation of the literature

The available data concerning the relationship between occlusal

disharmony and bruxism are inconclusive. The evidence from epidemio-

logical studies tends to support this theoretical relationship, but it

is clear that not all bruxing (MPD) patients have readily apparent

malocclusion and not all people with clinical malocclusion brux or

have facial pain (Olkinuoura, 1969; Schwartz, 1958). In addition,

epidemiological data are only minimally helpful when articulating

cause-and-effect statements since muscle hyperactivity and TMJ dis-

orders can lead to occlusal abnormalities as well as vice versa.

The evidence from experimental studies shows that occlusal

abnormalities can produce facial muscle hyperactivity and pain but it

is clear that the relationship is not simple or straightforward. Each

person's differential ability to adapt to various forms of masticatory

system disturbances seems to be an important factor. Methodologically,

the absence of placebo interference conditions is a serious design

flaw in all the experimental studies. Anatomically, the manifestation

of tooth-to-tooth relationships and of facial muscles during the act

of inserting an interference might have effects above and beyond those

of the interference itself. Psychologically the act of an experimenter










inserting a foreign object into a person's mouth might create behavioral

influences similar to demand effects (Orne, 1962). The study by

Magnusson and Enbom (1984) which included a simulated interference

condition, controlled for unwanted anatomical effects. However, since

no foreign object was actually left in, that study did not adequately

control for demand effects. In addition to the demand/placebo problem,

the various experiments have been characterized by routine shortcomings

such as inadequate sample sizes and weak measurement. On the whole,

a prudent characterization of the occlusal disharmony theory is that

it is overly simplistic and in need of further and better research.


Psychological Theories

There have been numerous attempts over the years to explain

bruxism using the concepts of psychology. For convenience and narrative

clarity, the psychological literature is divided here into psychoanaly-

tic/personality theories and psychophysiological theories. As

with the section on local factors, studies which have used relevant

dependent or covariate measures other than masticatory muscle activity

are included.


Psychoanalytical/personality theories

Many analytically oriented psychologists argue that bruxism is

a releasing mechanism for repressed oral aggression (Pond, 1968; Ramadan,

1970). Another analytic investigator suggests that the oral symptom of

bruxism results from guilt concerning sexual conflict (Moulton, 1955).

According to Lefer (1966), bruxism is a conversion reaction in which











ambivalent feelings concerning dependency needs and unacceptable

hostility are displaced through symptoms of the oral cavity. "Data"

supporting these psychodynamic formulations have typically come from

clinical/anecdotal reports. While this type of analysis might be

useful at some level, it is of limited scientific value because psycho-

dynamic constructs are insufficiently tied to observable phenomena.

Personality psychologists have posited a number of personality

characteristics and emotional traits relating to bruxing behavior.

In two similar studies, profiles from the Minnesota Multiphasic

Personality Inventory (MMPI) were compared for successfully and unsuc-

cessfully treated MPD patients (Schwartz, Greene, & Laskin, 1979;

Millstein-Prentky & Olson, 1979). Results from the two studies

revealed similar configurations for both groups of patients, but the

profiles of the unsuccessfully treated groups were significantly

higher than were those of the successfully treated groups. Additionally,

the "3-1-2" MMPI code types found for the MPD patients is essentially

the same as that found for patients presenting with psychophysiological

disorders such as low back pain (e.g., Sternback, Wolf, Murphy, &

Akeson, 1973).

DeBoever (1973) reviewed the findings from a number of studies

of personality characteristics among facial-pain patients and argues

that MPD patients as a group have conflicts related to dependency and

dominance and/or they try to maintain a rigid self-concept of normalcy

and strength. In a more recent and more thorough review, Rugh and

Solberg (1976) argue that the data are not nearly that clear cut or










simple. On the contrary, Rugh and Solberg concluded from their review

that "TMJ patients do not form a well-defined group with respect to

personality characteristics" (p. 9).

Generalized anxiety is one personality factor that has been

implicated consistently in the etiology and/or maintenance of bruxism.

The relevant studies have compared anxiety among bruxing/MPD patients

with anxiety among control groups. Molin, Edman, and Schalling (1973),

Solberg, Flint, and Brantner (1972), and others have shown MPD patients

to be more anxious than control groups. This approach is generally

problematic for at least two reasons. First, the traumatic effects

of bruxism might augment as well as result from anxiety. Secondly,

high anxiety might be associated with a third variable such as being

in anxiety-provoking jobs. Finally, although studies have shown

significant relationships between anxiety and facial pain, typically

the anxiety levels of these patients do not fall outside the range of

normal profiles (Rugh & Solberg, 1976). For these reasons, more

specific and detailed approaches to investigating the association between

bruxing behavior and anxiety are required.


Psychophysiological theories

The psychophysiological literature within dentistry has shifted

over the years, away from global personality-trait approaches toward a

conceptualizing of bruxism as a psychophysiological disorder. The

psychophysiological theories of bruxism have focused primarily on the

role played by stress.










Stress. Although stress is a familiar word, there is no single

definition or conceptualization that is acceptable to all professionals.

According to Cox (1978), stress has been used to denote a person's

response to a noxious stimulus, to denote the stimulus characteristics

of a noxious environment, and to denote a lack of fit between the person

and the environment. The most prominent proponent of the position that

stress is best viewed as a response is Selye (1974), who states that

stress is a "nonspecific response of the body to any demand made upon

it" (p. 14). There is a very large literature that uses an engineering

model in terms of which stress is viewed as a stimulus. For one example,

Welford (1973) used stress or demand upon the organism as an independent

variable and was able to show that performance efficiency followed an

inverted U-shaped function; maximum efficiency occurred during a

moderate demand condition.

As noted, a third approach to defining the concept of stress

takes as a point of departure the system of interactions between the

person and the environment. Two of the more prominent models within

this framework have been developed by Cox (1978) and Lazarus (1977).

The description of stress proposed by Cox draws from both the response-

and stimulus-based definitions described above but it underscores the

importance of the ecological and transactional quality of the stress

phenomenon. Cox states that "stress is an individual perceptual

phenomenon rooted in psychological processes" (p. 18). In this trans-

actional model he describes five distinct stages. The first stage

is comprised of demands on the individual, demands that might be










external (environmental) or internal (physiological). The second stage

involves the person's perception of the demand and of his perceived

capabilities for dealing with the demand. An imbalance is created if,

after cognitively appraising the possibly stressful situation, an

individual realizes his or her inability to cope. This imbalance is

followed by the subjective experience of stress and by the physiologi-

cal changes which form the third stage. Cox's fourth stage encompasses

the actual and perceived consequences of the coping responses. The

final stage revolves around the feedback mechanisms that are involved

continuously and that occur at the psychological/biological, social/

behavioral, and/or phenomenological/cognitive levels.

The second and probably best known of the interactional/cognitive

approaches to stress has been proposed by Lazarus and his colleagues

who suggest that the essential stress mediator is psychological.

Lazarus (1977) writes that "cognitive appraisal of harm via cerebrally

controlled processes is necessary to initiate the body's defensive

adrenal cortical response" (p. 14). Similarly, Lazarus, Cohen, Folkman,

Kanner, and Schaefer (1980) argue that the distinction between stress

viewed from the social and physiological levels and stress viewed at a

psychological level is the idea that people cognitively appraise adap-

tational interactions with their environment according to the signifi-

cance those interactions have for their wellbeing. This approach

allows for the distinction between the objective nature of a potentially

stressful event and the subjective evaluation of the event.

Stress-related theories of bruxism. Laskin (1969) proposed the

first comprehensive psychophysiological theory of bruxing in his











influential paper on the MPD syndrome. According to Laskin's theory,

the factor primarily responsible for facial pain among MPD patients is

spasm in the muscles of mastication. These spasms are said to

result from muscular overextension, muscular overcontraction, or

muscular fatigue. Some of these muscular anomalies, particularly

muscle fatigue, are said to result from stress-related oral-motor

habits such as tooth clenching or grinding. Hence the connection

between stress and bruxing is basic to Laskin's proposed diagnostic

entity of the MPD syndrome.

Yemm (1979) included both occlusal disharmony factors and

psychophysiological factors within a four-part typology for muscular

hyperactivity in craniomandibular disorders. "Habitual activity" is

related to the structure of the masticatory system. Facial muscle

activity is maintained in order to ameliorate the effects of untoward

morphological characteristics (e.g., occlusal disharmony as previously

discussed here). "Stress-induced muscle activity" refers to hyperac-

tivity of psychophysiological origin. Yemm's stress-related theory

is partly grounded in work that shows relationships between stress and

muscular activity in general (e.g., Lacey, Bateman, & Van Lehn, 1953;

Malmo, Shagass, & Davis, 1950). It also derives from work in which

bruxing-like behavior was produced in animals via electrical stimula-

tion of the brain (e.g., Kawamura, Tsukamoto, & Miyoshi, 1961; Landgreen

& Olson, 1977). Yemm argues for a direct relationship between external

stimulation, cortical and subcortical activation, and jaw muscle

hyperactivity.











There is a sizable literature examining the relationship

between stress and oral-motor behaviors such as bruxing. Masticatory

EMG activity, mandibular postural activity and various signs and

symptoms of mandibular dysfunction have all been used as dependent

and/or covariate measures. The following narrative is divided into two

categories: correlational/naturalistic and experimental/quasi-

experimental studies.

Correlational/naturalistic studies. Moody, Calhoun, Okeson,

and Kemper (1981) compared subjective assessments of stress and pain

among MPD patients versus non-MPD patients. The results pointed to

significantly higher levels of stress as well as pain among the MPD

patients.

Rugh and Solberg (1975) had bruxist subjects record nocturnal

masseter-area EMG activity for up to 40 nights. Following this, the

subjects were queried as to the occurrence of stressful events during

the days preceding high nighttime levels of EMG activity. For a number

of subjects, high levels of EMG activity were associated with stressful

daily events such as a school exam, news of a very ill sister, and a

job interview. Clark, Rugh, Handleman, and Beemsterboer (1977) had

bruxing subjects record nocturnal masseter-area EMG levels, rate daily

stress levels, and record the number of hours slept. Using a median

split, the data indicated that subjects with the lowest levels of per-

ceived diurnal stress showed the greatest amount of bruxing activity.

In a fairly unsophisticated single-subject design study, Funch and Gale

(1980) had a chronic female bruxer record her daytime stress and her










daytime activity levels, in addition to monitoring activity. Using a

multiple regression technique to analyze the data, the best predictor

of bruxing behavior was not stress, but what they called "anticipatory"

stress, that is, the stress score on the day after the recorded

bruxing. Funch and Gale hypothesized that "the subject might have a

general awareness of the next day's stresses and this anticipation might

have an influence on bruxing behavior" (p. 392).

Experimental/quasi-experimental studies. In one of the first

experimental studies on the stress-related theory of bruxism, Kydd

(1959) compared masseter and temporal EMG potentials, amplitudes, and

frequencies of 5 TMJ patients with those of 5 control subjects before,

during, and after a stressful interview. The stressful interview was a

discussion of emotionally charged material and traumatic events. The

results showed significant increases in EMG activity during the inter-

view among the TMJ patients but no such increases among the control

subjects.

In a series of experiments with normal subjects, Yemm (1968,

1969, 1971) showed that masseter and temporal EMG activity increased

during the performance of a task requiring concentration and accuracy.

The task required subjects to press different buttons corresponding to

six different lamps illuminated in random orders. As the difficulty

of the task increased, EMG activity also increased. Additionally, EMG

amplitudes increased significantly following mistakes in performance.

When the task of constant difficulty was presented repeatedly, EMG

magnitudes tended to decrease with successive attempts. Yemm (1969),










however, found that unlike normal subjects, TMJ patients showed no such

decrease in EMG activity over successive attempts when the difficulty

of the task remained constant.

Thomas, Tiber, and Schireson (1973) evaluated the effects of

both anxiety and frustration on masseter and temporal EMG activity

among 10 TMJ patients and 10 control subjects. Anxiety was produced

by exposing the subjects to painful electric shocks applied to the

medial side of the left forearm at unknown random intervals. Frustra-

tion was produced by blindfolding and instructing subjects to

complete a form board. At random intervals the subjects were

interrupted, comments were made about their poor cooperation and per-

formance, and they were told to begin the task again. The EMG activity

was measured for 90 s during the end of the anxiety and frustration

task periods. The data mirrored significantly higher changes in EMG

activity from baseline for the TMJ group than for the control group

during both the anxiety and frustration conditions. In addition,

the frustration condition resulted in significantly higher EMG changes

than did the anxiety condition for both the TMJ and control groups.

Finally, the group by condition interaction was significant; the TMJ

group in the frustration condition showed significantly higher EMG

change scores than did the other three group x condition pairs.

Rao and Glaros (1979) compared 10 self-reported diurnal bruxing

subjects to 10 normal subjects on masseter EMG and heart rate

responsivity to stress. The authors induced stress by having the

subjects complete the Modified Stroop test (Stroop, 1935) and the











Anagrams test (Mayzner & Tresselt, 1958). Stress also was induced by the

unexpected presentation of a loud noise for 10 s. The results showed

significantly higher baseline masseter EMG activity for the bruxist

subjects than for the normal subjects. No significant heart rate

differences between groups were found during any of the three stressful

conditions. In addition, no significant EMG differences were found

between groups for the Modified Stroop or Anagrams tests. In terms

of masseter EMGs, the bruxist subjects did respond differently more

to the loud noise than did the control subjects.

Mercuri, Olson, and Laskin (1979) measured masseter and

frontalis EMG activity, gastrocnemius (lower leg) muscle activity,

heart rate responses, and galvanic skin responses (GSRs) among 20 MPD

patients and 20 control subjects before, during, and after a series

of four stressors. The purported stressors included a 75 dec white

noise, a card sorting exercise, a word association task, and a pain

induction procedure. Baseline measures showed a significantly higher

resting level of masseter and frontalis EMG activity for the MPD

group than for the control group. Change scores were not used in the

analysis of the data and the baseline differences between groups were

maintained throughout the series of four supposedly stressful situa-

tions and on post-test measurements. No significant group or condition

differences were found for the heart rate and GSR measures.

Moss and Adams (1984) evaluated the effects of four stressors

on physiological responding among 10 TMJ patients and among two

matched control groups, one with TMJ sounds only and one with no history










of TMJ symptoms. The four stressors used were an unannounced loud

noise, a signaled series of loud noises, instructions to subtract

covertly successive "7s" beginning with 1,000, and a pain threshold/

tolerance test using ischemic pain from a blood pressure cuff. The

physiological measures used were bilateral masseter EMG, skin con-

ductance level, and heart rate. Skin conductance levels and heart

rates were significantly lower during pretask baseline periods in

comparison to the covert subtraction task and the pain threshold/

tolerance test, across all three groups. The masseter EMG data pro-

vided little support for the hypothesis that the three groups would

differ with respect to baseline levels or with respect to responsivity

to stressors. One supportive result was that TMJ subjects exhibited

significantly greater masseter EMG responsivity during the covert

subtraction task as compared to the two control groups.

Evaluation of the literature. In general, the correlational/

naturalistic studies examining the stress-related theory of bruxism

tend to be supportive, but not robustly so. Causal relationships

cannot be verified from correlational data. In addition, as noted

by Moss, Garrett, and Chiodo (1982), correlational studies which rely

solely on the retrospective self-report of patients are subject to

a number of methodological problems such as confabulations and errors

of omission.

In general, the experimental/quasi-experimental studies

examining the stress-related theory of bruxism seems to support a

relationship between stress and masticatory muscle activity among MPD










patients. However, a careful examination of the research presented

above and of the few, even less sophisticated studies not mentioned

here, reveals numerous methodological problems. The most consistent

finding of these and other studies is that bruxing/MPD patients show

higher baseline or resting EMG levels than do control groups. This

finding, however, has little to do with the role of stress. Further-

more, in using MPD patient-subject comparisons, it is unknown how

many patients are bruxers. Another difficulty with the above studies

is the use of stressful tasks requiring hand, head, and/or other body

movements which affect EMG activity in unwanted ways. Finally, when

using stress as an intervening construct it is important to show that

experimental representation of the construct did indeed take place.

Although it can be argued that finding predicted task-induced EMG

differences is sufficient to establish stress as an intervening

construct, it can be argued also that corroboration from stress

measures other than EMG is necessary for strong claims. Most of the

studies just reviewed incorporated no behavioral or self-report

measures of the effects of experimental stressors. Additionally,

except for Moss and Adams (1984), the heart rate and GSR measures that

were used produced no differences associated with the various

presumably stressful tasks. In brief, no strong statements can be made

about the stress-related theory of bruxism based on the experimental

data that are available.


Interactive Theories

Although the relevant research is more or less uniformly weak

methodologically, influential statements have nonetheless been made










that both malocclusion and stressful life events can lead to abnormal

masticatory muscle activity. As Ramfjord and Ash (1983) have

pointed out, essentially everyone has some type of occlusal inter-

ference, yet few people have problems with bruxism. Further, these

people typically have problems only during certain periods in their

lives. This state of affairs has led to arguments that bruxism

results from an interaction of anatomical, physiological, and

psychological factors. For one example, Ramfjord and Ash posit a

tolerance threshold to occlusal interference that varies within and

between individuals. They argue that "psychic stress" can lower this

tolerance threshold leading to jaw muscle activity caused by occlusal

interference. For another example, Rugh and Solberg (1976) posit

that the origin of facial pain is specific microtraumatic lesions

produced by maladaptive oral behavior. In turn, the dysfunction

involves the unique interaction of structural (e.g., temporomandibular

articulation), behavioral (e.g., neuromuscular performance), and

psychological (e.g., perception of potentially stressful event) fac-

tors. For example, instability in gnathic structures due to injury,

occlusal interference, genetic, and/or developmental factors may

produce a susceptible individual who responds to perceived stressful

stimuli within the stomatognathic system.

McGlynn, Cassisi, and Diamond (in press) draw a parallel

between etiological theories of bruxism and other disorders such as

low back pain, tension headache, and tic spasmodic torticollis. They

argue that in each case, controversy exists when evaluating organic











versus functional contributions to the signs and symptoms of the

disorders. In these instances and certainly with regards to bruxism,

an interactive theoretical stance is to be preferred since it focuses

importance on an interdisciplinary approach to research, diganosis,

and treatment.


Empirical Status

No experiment has evaluated an interactive theory of bruxism.

No experiment has manipulated simultaneously both the variable of

malocclusion and the variable of stress. No doubt the interactional

or multifactorial theoretical approach is true. However, it is far

too general to be of enduring value in its present form. Nothing is

known confidently about what types of occlusal factors interact with

what types of stressors, for what time periods, in conjunction with

what other variables, and so forth. Obviously, there is a need for

truly massive programmatic research directed toward empirically

fleshing out the general view that occlusal disharmonies, psychobio-

logic stress, and other factors interact to produce clinically sig-

nificant elevations in masticatory muscle tension.


Rationale of Present Experiment

The main purpose of the present study was to examine experi-

mentally the unilateral and interacting effects of malocclusion and

psychological stress on masseter muscle activity. The variable of

malocclusion was produced by attaching an occlusal interference

(splint) to the subjects' teeth. A placebo interference (splint)










condition was incorporated into the study to control for the act of

inserting a foreign object into a subject's mouth. Simultaneously,

the variable of stress was produced by having subjects observe brief

film clips taken from horror movies. Neutral (nonstressful)

picturesque film clips were incorporated into the study to control for

the effects of movie watching per se. To reduce possible effects

from an orienting response, each film was shown for 1 min 40 s before

data collection began. A within-subjects design was utilized such

that each subject was exposed to all four pairs of experimental condi-

tions: (a) interference splint/stressful movie, (b) interference

splint/neutral movie, (c) placebo splint/stressful movie, and (d) pla-

cebo splint/neutral movie.

Masseter EMG measures in microvolts (uvs) were taken bilaterally

so that activity ipsilateral (EMGI) and contralateral (EMGC) to the

splint could be examined. The bandpass for the electromyograph was

set at 400-500 Hz. This bandpass was selected since it detects muscle

activity within relatively localized areas, in this case within the

masseter muscles. The scale selector for the electromyograph had a

lower end of 0.5 iv and an upper end of 10.0 pv. Pilot data using

this electromyograph indicated that masseteric activity under non-

strenuous conditions typically falls within this range (Mealiea, 1984).

Attempts to establish stress as in intervening construct

independent of the EMG data also were made. These took the form of

obtaining skin conductance measures during and self-report anxiety

measures after viewing the various films. Skin conductance refers to











the electrical conductivity of the skin when a constant voltage is

applied. Skin conductance level (SCL) is the absolute value of

electrical conductivity measured over a given skin area. Skin con-

ductance response (SCR) is a momentary change in SCL that results from

presentation of discrete stimuli. Both SCL and SCR data were recorded

before and throughout both types of films viewed in the experiment.

Attempts to document the experimental manipulation of.malocclusion

were made in two ways. First, laboratory and clinical examinations

were performed to insure that the interference splints produced a

balancing side interference and only a balancing side interference and

to insure that the placebo splints did not produce any type of occlusal

interference. Secondly, a self-report questionnaire was created for

the experiment in order to assess painful or irritating effects produced

by the splints.

Finally, as noted, very little research of this type has been

undertaken previously and no experimenter using human subjects has

attempted to manipulate the variables of malocclusion and stress

simultaneously. For this reason there were few sources of information

to guide decision making at various methodological choice points.

Given this state of affairs, an alpha level of .10 was chosen as con-

sistent with the somewhat exploratory experimental purpose.













CHAPTER TWO
METHOD


Subjects

Subjects were recruited for a "dental study" via public notices,

classroom announcements, and personal contacts. They were required

to be female, to be between 18 and 35 years of age, to be not pregnant,

to be in good health, and to have normal occlusion. Volunteers were

initially subjected to a brief history taking and to a dental assessment.

The history taking included questions pertaining to present and/or

past experiences with the following symptoms: facial pain, joint sounds,

limitations in opening the mouth wide, pain on movement of the mandible,

and nocturnal teeth grinding. Any subject reporting a history of one

or more of these symptoms during the past year was excluded. The

dental examination included an assessment of the subjects' occlusion

in both centric occlusion and centric relation. In addition, the

clinical assessment investigated pathognomic tooth wear, abnormal tooth

mobility, bony joint damage, joint sounds, joint tenderness, and dental

infections. Subjects were recruited until 8 females were accepted who

had normal occlusion, no more than one missing tooth per quadrant, no

evidence of pathognomic tooth wear, no evidence of abnormal tooth

mobility or bony joint damage, no significant occlusal interference, no

clinical signs of dysfunction, and no reported history of bruxism or

MPD symptoms during the previous year. Six potential subjects were

excluded.











Potential subjects who met these requirements were provided

with a complete description of the project in the form of an informed

consent document. In the document they were told that on two separate

occasions, a small appliance, similar to a crown, would be attached to

two of their teeth. They were told also that, some hours following

attachment of each crown, they would be asked to sit and watch film

clips of both picturesque and horrible scenes. They were informed also

that, during the film presentation, they would be seated comfortably

in a soft chair with nonpainful surface electrodes attached to their

face and hand. They were told also that, following the film presen-

tation, they would complete a questionnaire concerning their reaction

to the films at which point the appliance would be removed. Finally,

they were told that $30.00 would be paid for their participation. The

8 subjects who were selected were secretaries, technicians, and non-

dental students with a mean age of 24.4 years. All subjects signed the

informed consent agreement which stated clearly that they were free to

discontinue participation at any time.


Experimenters

All dental procedures involving subject contact were conducted

by Harry C. Lundeen, DDS. All other procedures involving contact

with the subjects such as subject scheduling, history taking, and

psychophysiological recording were conducted by a clinical psychology

graduate student.











Apparatus

Electromyograph

Masseter muscle activity was measured bilaterally using two

Autogen 1700 electromyographs (Autogenic Systems, 1975). The six

surface electrodes were 1 cm in size, were made of silver/silver chloride,

were embedded in plastic insulator disks, and were attached to a

shielded cable. After cleansing of the face the four active electrodes

were placed bilaterally at the angles of the mandible and 2 in. above

the angles of the mandible. The two ground (reference) electrodes

were placed midway and 2 in. anteriorly to the active electrodes. The

EMG data, in microvolts (pvs), were printed out by an Autogen 5600

Integrator that provided an average for each 40 s of activity.


Electrodermoqraph

The SCLs and SCRs were measured in micromhos (pmhos) with an

Autogen 3400 electrodermograph (Autogenic Systems, 1975). Three

recessed gold alloy surface electrodes were attached to the skin via

Redux electrode contact gel and adhesive disks. Following cleansing

of the hand, the two active electrodes were attached to the palmar

surface of the left hand, while the third (reference) electrode was

attached to the dorsal surface. The electrodermograph also was attached

to theAutogen 5600 integrator which again provided an experimental

average of the activity for each 40-s period.


Placebo and Maloccluding Interferences

Both an interference splint and a placebo splint were made for

each subject. The interfering splints and six of the eight placebo











splints were built on mandibular first or second molars. Due to limited

mandibular space, two of the placebo splints were built on the

maxillary second premolar and first molar. For each subject the

placebo splint was built for one side while the interference splint

was built for the other. The side was counterbalanced for the 8 subjects

such that four placebos and four interference were attached to the

right side and four placebos and four interference were attached to

the left.

In order to begin designing each splint, a wax registration

and a cast of the subject's teeth were made then mounted on a dental

articulator (mechanical cast holder) in centric relation. The cast was

then surveyed and the best possible undercut for clasp retention was

found. For each subject the placebo splint was designed first so as

to utilize the embrasure (the space between the marginal ridges of

opposing teeth) that provided the greatest interocclusal space. Follow-

ing this procedure it was possible to design, for all 8 subjects, a

placebo splint which created no interference of any kind. As noted,

the interference splint was then designed for the opposite side. The

only difference between the two splint designs was that the interference

splint contained an occlusal extension that covered part of the biting

surface and prevented occlusal contact vis-a-vis the remaining teeth

(see Appendix A). Specifically, a ramp was designed to be built over

the lingual incline of the mandibular buccal cusp creating a balancing

side interference. For example, using this design, an interference on

the left side would disocclude the teeth on the right (working) side











during right lateral excursion, leaving contact only between the inter-

fering teeth on the left (balancing) side.

Once the splints were designed, the master cast was duplicated,

using a reversible hydrocolloid, which was then invested using Ticonium.

Tacky wax was then applied to this refractory cast in the areas to

which the plastic patterns would be adapted. Patterns were then sprued

to the area of greatest bulk, invested and, through the "lost wax

method," the splint was produced. Following removal of the sprue, the

splint was quartz blasted, electropolished, and seated on the master

cast. For the placebo splint, a check using the articulator was then

made to insure that it produced no interference of any kind. For the

interference splint, a check was made to insure that a balancing side

interference and only a balancing side interference existed.


Neutral and Stressful Films

Two stressful film clips and two neutral (nonstressful) film

clips were played on a Sony videocassette recorder (VCR) and viewed on

an Electrohome television monitor. Each lasted 7 min 40 s. These film

clips are stored in the University of Florida, Department of Basic Dental

Sciences film library.

The two nonstressful film clips were visually picturesque scenes

from the movie Jonathan Livingston Seagull. They included scenes in

which the seagull flew over the ocean, desert, and mountains. Music by

Neal Diamond accompanied these scenes. These film clips were chosen

subjectively. One of the two stressful film clips was made using three

scenes from the movie Dawn of the Dead. The second stressful film clip











was made using two scenes from the movie Psycho II. Both movies con-

tained scenes in which people were shot, stabbed, decapitated, and

otherwise physically mutilated. These film clips also were chosen

subjectively.


Anxiety Differential

The Anxiety Differential, a self-report semantic differential

type questionnaire developed by Husek and Alexander (1963), was used to

evaluate subjects' emotional responses to the film clips. The 18-item

bipolar adjective questionnaire with anchor points from 1 to 7 has been

shown to be sensitive to emotional arousal following movie viewing

(Alexander & Husek, 1962).


Pain and Irritation Questionnaire

A corroborative measure developed for this experiment was a pain

and irritation questionnaire. This 10-item self-report questionnaire

(see Appendix B) had two parts, one involving pain and the other

involving local irritation. The pain items involved asking subjects to

rate, on a scale of 0 to 10, the amount of pain and/or fatigue, if any,

they had in their facial or jaw muscles. The subjects rated their facial

pain five times: (a) before attachment of the appliance, (b) during the

evening when the appliance was in place, (c) approximately 19 hr after

the appliance was attached, (d) 2 hr after removal of the appliance, and

(e) 24 hr after removal of the appliance. The irritation ratings

occurred at the same five time periods and involved asking the subjects

to rate, on a scale of 0 to 10, the amount of tooth and/or gum irritation

in areas adjacent to the appliance.











Procedure

Individual appointments, during a 3-week period, were made for

the 8 subjects who met the criteria for normal masticatory system

functioning and who agreed to participate in the study. At these first

appointments, impressions and wax registrations of the teeth were taken.

The casts of the teeth were then made and mounted on the articulator.

The mounted casts were delivered to a dental technologist (Barry Nicholas)

who then fabricated the interference and placebo splints. When the

splints were ready, individual appointments were again made for subjects

and, on their arrival, they were fitted with one of the two splints.

(Half of the subjects received the interference splint first while the

other half received the placebo splint first.) Upon intraoral placement

of the interference or placebo splint a clinical examination, using

articulating paper and cellophane strips, was made to verify that the

splint had been designed and fabricated according to specifications.

Following clinical verification, a standard crown and bridge cement

was used to lute the splint to the teeth. Before leaving the dental

operator, an appointment was made for the next day (approximately

19 hr later) for the subject to view the films. Additionally, each

subject was instructed to check at least once after dinner and once just

before going to bed to make sure that the splint was securely in place.

On arriving at the laboratory the next day, the subject was

seated in a soft, reclining chair and asked to complete the second,

third, seventh, and eighth items on the pain and irritation question-

naire. Following this, the EMG and GSR electrodes were attached to the










subject's masseter muscles and hand, respectively. The subject was

then instructed to recline in the chair slightly, to keep her head

straight and against the back of the chair, to keep her eyes open, and

to move as little as possible. The subject was once again informed that

she would be viewing two film clips, one containing picturesque scenes

and one containing horrible scenes. Each subject was told also that it

would take 8 min for the machine to warm up and during this period she

was to relax and think comforting thoughts. The experimental period

began 2 min later and continued for approximately 35 min spanning five

experimental phases each of which was 6 min long. As noted earlier,

each movie was actually shown for 7 min 40 s. Recording was delayed

for 1 min 40 s to attenuate effects from orientation. The five 6-min

recording periods consisted of (a) baseline 1, (b) neutral or stressful

movie viewing, (c) baseline 2, (d) neutral or stressful movie viewing

[whichever did not occur in period (b)], and (e) baseline 3. Following

the first two baseline periods the experimenter entered the laboratory

briefly, to activate the VCR and tell the subject that the first (or

second) film clip was about to come on. Following the initial movie

viewing period the experimenter entered the laboratory briefly to de-

activate the VCR and tell the subject that the second film clip would

be shown in 6 min. Following the second movie viewing period the

experimenter entered the laboratory briefly to deactivate the VCR and

tell the subject that this phase of the experiment would be over in6 min.

During Session 1 all subjects viewed the same Jonathan Livingston

Seagull film clip and the Dawn of the Dead film clip in one of the two











possible orders. During Session 2 all subjects viewed the second

Jonathan Livingston Seagull film clip and the Psycho II film clip again

in one of two possible orders. Over the 8 subjects the testing order

for the splint and movie conditions was completely counterbalanced.

(A copy of the specific testing order for each subject is provided in

Appendix C.) Following the third baseline period the electrodes were

removed and the subject was asked to complete twice the Anxiety Differ-

ential, once with respect to her response to the first film and again

for the second film. Each subject was then escorted to the dental

operator where the splint was removed. Two and 24 hr later, each

subject was contacted and asked to complete the fourth and ninth items

and the fifth and tenth items, respectively, from the pain and irrita-

tion questionnaire. Beginning with the intraoral placement of the

splint, all 8 subjects went through this entire procedure twice, once

for the interference splint and once for the placebo splint. The two

testing sessions were separated by at least 1 week.















CHAPTER THREE
RESULTS


Data Concerning Experimental Validity

Multiple measures of stress and multiple examinations of splints

were prompted by a concern for experimental validity. Regarding the

stress manipulation, the experiment is independently valid insofar as

stress measures other than EMG show that levels of stress were varied.

To evaluate independently whether the film manipulation was a stress

manipulation, skin conductance measures were taken during film viewing,

and a self-report anxiety measure was taken afterwards. Regarding the

occlusal manipulation, the experiment is independently valid insofar

as measures other than EMG show that malocclusion was varied. To

evaluate independently whether the splint manipulation was an occlusal

disharmony manipulation, laboratory and clinical examinations were

performed on the splints. In addition, subjects' reactions to the

splints were evaluated via the pain and irritation questionnaire. The

design of the experiment is such that validation of both the stress and

malocclusion manipulation amounts to validation that the interaction of

these two factors was experimentally possible. The narrative within

this section reports the statistical, clinical, and laboratory analyses

performed on the various data concerning experimental validity.










General Analysis Strategy

Each subject provided data from two different sessions and

might have differed at the beginning of each. Hence, analyses of

within-session change scores as well as raw scores for the two sessions

were performed. Change score data are obtained by subtracting baseline

data from task-related data within a session. Since each session

within the experiment incorporated a baseline period before each of the

two movies, selection of one baseline was required prior to data

analysis. Due to the problem of potential habituation during the base-

line period, a decision concerning sampling from all or only part of

the chosen baseline was required also.

In order to select a within-session baseline, means representing

the entire 6 min for each subject were calculated and t tests for cor-

related samples (Ferguson, 1971) were used to compare baseline 1 (Bl)

with baseline 2 (B2) mean SCL data within each session. The results

indicated that for both Session 1 [t(7) = 3.39, p < .02] and Session 2

[t(7) = 3.96, p < .01], B1 was significantly lower than B2. (The means

and standard deviations are presented in columns one and two of Table

3-1.) The lower within-session baseline SCL (B1) was chosen as the

reference baseline for all SCL change score analyses. In order to choose

a baseline sampling strategy within each subject's B1 SCL data set,

regression analyses (Kirk, 1968) were performed across the nine measure-

ment intervals. The r values and F statistics (column 1 in Table 3-1)

clearly indicated that habituation was occurring. A visual examination

of the data presented in Tables D-1 and D-2 indicated that at about the












Table 3-1 Means, standard deviations, r values, and F statistics from
B1 and B2 regression analyses, for SCL (in pmhos), EMGI,
and EMGC (in pvs), grouped by session


SCL EMGI EMGC

B1 B2 B1 B2 B1 B2

Mean 9.19 12.24 1.23 1.37 1.73 1.79

(sd) 6.03 6.49 0.74 .77 1.17 1.08
Session 1
r value .16 .17 .11 .07 .01 .01

F statistics .18 .15 .38 .56 .92 .91
-------------------------------------------------------------
Mean 7.59 11.41 1.24 1.09 1.28 1.38

(sd) 5.70 6.63 0.66 0.53 0.70 0.54
Session 2
r value .17 .15 .09 .02 .01 .08

F statisticb .16 .21 .46 .88 .93 .51


aThe higher the r value, the greater the correlation

bThe lower the F statistic, the greater the significance











sixth interval habituation began leveling off. Consequently, the last

four measurement intervals (a total of 160 s) were chosen as the

reference points for calculating individual mean baseline (B1) SCL

values (see Table D-3).

In summary, the nature of the study prompted the use of change

score analyses in addition to raw score analyses within the SCL data.

Based on statistical and visual examinations, the mean of the last four

measurement intervals of B1 represented the most meaningful baseline

measure.


Skin Conductance Data Analyses

For each subject a mean SCL during each 6 min movie was calcu-

lated by averaging the SCL across the nine measurement intervals. Using

a Randomized Block (RB-4; Kirk, 1968) design, a one-way ANOVA with

repeated measures was then computed on baseline referenced change

scores produced by the four movies (see Table D-4). The result was

significant, F(3,21) = 7.89, p < .01. A post hoc analysis using

Duncan's test was performed with respect to the change score means

presented in Table 3-2. The analysis indicated that both stressful

movies produced significantly higher skin conductance levels than did

both neutral movies. The two stressful movies did not differ from each

other nor did the two neutral movies.

In order to characterize the SCL data further, analyses of raw

score means as well as change score means were performed. Using a

Randomized Block (RB-6; Kirk, 1968) design, raw SCL means from each







44





















ao i








E








o -0












4- Q


co
a 0
*l o- "
-'- C "


















0-
ro S/)












0






i I .,
3- ".







S--
Co e 0







c--
m "
U t to to














-0 I
2 _



SI -. i|










O -





ni S
-o 0





In U 1 t .1 1/1






I^t 5- c.










of the four movies and from the two baseline (B1) periods (see Tables

3-2 and 3-3 for summarized data) were subjected to a one-way ANOVA with

repeated measures (see Table D-5 for data actually analyzed). The

result from this analysis also was significant, F(5,35) = 5.59, p < .01.

A Duncan's test revealed again that the stressful movies were not sig-

nificantly different from each other but that both produced significantly

higher raw SCL means over the nine intervals than did the neutral

movies. Additionally, as would be expected from the change SCL analy-

ses (presented above), the SCLs for the stressful movies were higher

than for the baseline (B1) periods. There were no significant

differences between the raw SCL means during the neutral movies and

the baseline (Bl) periods.

Finally, a one-way ANOVA with repeated measures, based on an

RB-6 design, was computed on the numbers of SCRs that occurred during

each of the four movies and during the two baseline (Bl) periods (see

Tables 3-2 and 3-3 for summarized data; see Table D-6 for actual data

analyzed). The result from this analysis also was significant

F(5,35) = 6.99, 2 < .01. The results from a Duncan's post hoc analysis

were exactly the same as for the raw SCL data. The two stressful

movies did not significantly differ from each other but they both pro-

duced a greater number of SCRs than did either of the two neutral

movies. Also the numbers of SCRs during the stressful movies were

significantly higher than were the numbers of SCRs during the two base-

line (B1) periods. Finally, the number of SCRs during the two neutral

movies were not significantly different and neither differed from the

numbers of SCRs during the baseline period.










Table 3-3.


Means and standard deviations for raw B1 SCL (in umhos)
and total number of B1 SCRs grouped by session


SCL SCR

Session 1 Session 2 Session 1 Session 2

8.30 6.79 27 9

(4.84) (4.77) --- ---




Table 3-4. Means and standard deviations for self-reported anxiety
based upon the Anxiety Differential, grouped by four
movies


Stressful Movies Neutral Movies

Dawn of
the Dead Psycho II J.L.S. I J.L.S. II
(Session 1) (Session 2) (Session 1) (Session 2)

80.9 75.1 46.4 44.9

(17.8) (21.2) (10.1) (11.8)


Note. J.L.S. I represents the first Jonathan Livingston Seagull movie;
J.L.S. II represents the second Jonathan Livingston Seagull
movie.


Table 3-5.


The summed total of self-report responses based upon the
pain and irritation questionnaire, grouped by response
type and splint condition


Pain Local Irritation

Interference Placebo Interference Placebo
Splint Splint Splint Splint

14 6 51 36










Overall, the analyses of electrodermal data show clearly that

differing film content influenced electrodermal flow dramatically.

At the levels of SCL and SCRs, the experiment did succeed in manipu-

lating levels of stress as required by the logic of the design.


Anxiety Differential Data Analysis

As noted earlier, the 18-item Anxiety Differential was completed

by each subject with respect to each of the four movies. A repeated

measures one-way ANOVA (RB-4) within the Anxiety Differential scores

was significant F(3,21) = 17.5, p < .01 (see Table 3-4 for summarized

data; see Table D-7 for actual data analyzed). A post hoc analysis

using Duncan's test indicated that subjects' experienced anxiety

(arousal) levels were significantly higher during the stressful movies

than during the neutral movies. Additionally, the stressful movies

did not significantly differ from each other nor did the neutral movies.

Hence, data from the Anxiety Differential corroborate the electrodermal

data in showing that stress was manipulated successfully by varying the

film content used in the experiment.


Laboratory and Clinical Examinations of the Splints

As noted previously, the effects of the splints on tooth-to-

tooth relationships and functional activity were assessed independently,

twice during the experiment. The first was a laboratory assessment

performed by a dental technologist. Following fabrication of the indi-

vidual splint it was seated on the master cast which remained mounted

on an articulator in centric relation. Selective grinding of the











interference splint was then performed so as to produce a proper fit

and to limit splint thickness to a maximum of 1.00 mm. Measurements

showed the thicknesses of the occlusal extension on the interference

splints to range from 0.75 mm to 1.00 mm. Selective grinding of the

placebo splints was performed so as to eliminate interference vis-a-

vis articulator movements. The second assessment was a clinical

assessment performed by a dentist. Prior to cementing the splint,

it was placed in the subject's mouth and, with the aid of articulating

paper, a clinical examination was performed. For the interference

splints, any type of interference other than balancing side inter-

ferences were removed. For the placebo splints, in three instances a

slight interference was noted and promptly removed. Hence the manipula-

tion of occlusal interference versus no interference was accomplished

as evaluated with one laboratory and one clinical procedure.


Pain and Irritation Data Analysis

The.logic of the experiment required not only that the placebo

splints be devoid of occlusal interference, but also that they be

neutral or without impact of any kind other than controlling for the

factor of splint placement. Hence subjective ratings of the effects

of the placebo splints as well as the interference splints were

obtained via the pain and irritation questionnaire. As noted, this

10-item self-report questionnaire had two parts, one concerning the

experience of pain and the other concerning local irritation. Using

a 0 to 10 rating scale,-the subjects rated both pain and irritation five

times for the interference splint and five times for the placebo splint.










For each of the 8 subjects, the ratings for the five periods were

summed producing eight totals for the following four combinations:

(a) facial pain/interference splint, (b) facial pain/placebo splint,

(c) local irritation/interference splint, and (d) local irritation/

placebo splint.

A one-way ANOVA with repeated measures (RB-4) was used to

analyze conjointly the summed self-report ratings of pain and of irri-

tation. The result was significant F(3,21) = 3.52, p < .05 (see

Table 3-5 for summarized data; see Table D-8 for actual data analyzed).

A Duncan's test revealed that local irritation from the placebo splint

was not significantly lower than was local irritation from the inter-

ference splint. The same was true of pain ratings for the two splints.

The significant one-way ANOVA reflected differences between irritation

scores for the interference splint and pain ratings for the two

devices. These reports concerning pain and irritation are potentially

problematic from the vantage point of design logic. While the placebo

splint did not occasion any occlusal interference, it was not com-

pletely neutral or inert within the oral cavity.


Summary of Data Concerning Experimental Validity

As noted the analysis performed on the electrodermal data and

on the Anxiety Differential data showed that the stressful movie content

produced greater arousal than did the neutral movie content. These

results provide two domains of clear experimental support for saying

that levels of stress were successfully manipulated within the experi-

ment. In addition, the laboratory and clinical examinations performed











on the splints indicated that the variable of malocclusion was satis-

factorily manipulated in the experiment. Problematically, the pain

and irritation data suggest that the splints did not differ substan-

tially with respect to oral factors other than occlusion per se. Since

the placebo was not inert, the design of the experiment is somewhat

compromised, notwithstanding the successful manipulation of occlusal

interference.


Data Concerning the Experimental Manipulations

General Analysis Strategy

As noted previously, each subject provided data from two

different sessions and might have differed at the beginning of each.

Hence, analyses of within-session change scores as well as raw scores

for the two sessions were performed. As with the data concerning

experimental validity, decisions concerning the selection of an EMG

baseline and the selection of all or part of the chosen baseline were

necessary. In order to select an EMG baseline, EMG data ipsilateral to

the splint (EMGI) and EMG data contralateral to the splint (EMGC)

were considered separately. For each data set, means representing

the entire 6 min for each subject were calculated and t tests for

correlated samples (Ferguson, 1971) were used to compare B1 versus B2

means within each experimental session. (The means and standard devia-

tions for EMGI and EMGC at B1 and B2 within each session are presented

in columns three, four, five, and six of Table 3-1.) The t tests for

the EMGI data yielded differences within Session 1 [t(7) = 2.05, < .10],

indicating that B1 was significantly lower than B2. The results for











the Session 2 EMGI data was nonsignificant, t(7) = 1.12. The t tests

between B1 means and B2 means for the EMGC data yielded nonsignificant

results for both Session 1 [t(7) = 0.42] and Session 2 [t(7) = 1.03].

Although only one of the four t tests was significant and it was only

marginally so, the mean for B1 was lower than the mean for B2 in three

of four comparisons. Hence B1 was chosen as the baseline measure for

both ipsilateral and contralateral EMG change score analysis. As an

aid in determining which part of the baseline (Bl) was to be sampled

from, regression analyses (Kirk, 1968) were performed across the nine

measurement intervals in B1 during Session 1 and Session 2 for both

the EMGI and EMGC data. (The r values and F statistics are presented

in columns three and five of Table 3-1.) The results did not reveal

any consistent habituation for EMG (see Tables D-1 and D-2). However,

in order to be consistent with the SCL analyses, the last four intervals

(a total of 160 s) were chosen as the reference point for calculating

individual mean baseline (Bl) EMGI and EMGC values (see Table 0-3).

In summary, the nature of the study prompted the use of within-

session change score analyses as well as raw score analyses. Based on

statistical and visual examinations of the data and to be consistent

with the SCL data analyses, the average of the last four intervals of

B1 was chosen as the within-session baseline for both ipsilateral and

contralateral EMG values.


EMG Data Analysis

In addition to the two 160-s mean B1 EMG values ipsilateral and

contralateral to the splint (above), each of the 8 subjects provided











one ipsilateral and one contralateral EMG value for each of nine 40-s

periods during each of the four movies. These 576 EMG values comprised

one data set. The raw values also were transformed into 576 baseline

referenced change scores to constitute anotherdata set. The two data

sets were evaluated separately by identical 2 x 2 x 2 x 9 (splint x

movies x sides x intervals) ANOVAs in which there were repeated measures

on all factors and in which the mean square residual was partitioned

into its component interactions (Kirk, 1968, p. 242). The results for

the two ANOVAs were very similar. Hence only the ANOVA for the within-

session change scores is presented here. (The means and standard

deviations generated during both ANOVAs are presented in Tables D-9

through D-18.) The ANOVA summary for change scores is presented in

Table 3-6. As can be seen in the table, there were significant main

effects on EMG for the movie content, the side of EMG recording and the

interval within the nine 40-s periods. Visual inspection showed that

the main effect for movie content mirrored greater EMG change-score

values during the stressful as opposed to the neutral films. The mean

EMG for 288 measurements during the stressful movies was 0.597 Pv,

while the mean EMG for 288 measurements during neutral movies was

0.359 pv. Visual inspection showed also that the main effect for side

of recording reflected greater EMG change scores contralateral to the

splints than ipsilateral to the splints. The mean EMG change for 288

contralateral measurements was 0.703 pv, while that for ipsilateral

measurements was 0.252 pv. Duncan's test was used to characterize the

significant main effect within the nine recording intervals. The 64 EMG


















Table 3-6. EMG change score summary table for 2x2x2x9 (splints
movies x sides x intervals) ANOVA with repeated measures,
using condition subject interaction as error term

Probability
Sum of Degrees of Mean F
Source Squares Freedom Square F Exceeded

Splints 8.225 1 8.225 0.36 .569

Splints x Subjects 161.604 7 23.086

Movies 8.143 1 8.143 4.00 .085*

Movies xSubjects 14.249 7 2.036

Sides 29.294 1 29.294 4.89 .063*

Sides xSubjects 41.918 7 5.988

Intervals 5.010 8 0.626 4.32 .001*

Intervals xSubjects 8.125 56 0.145

Subjects 82.195 7 11.742

Splints xMovies 0.042 1 0.042 0.09 .776

Splints xliov ies x Subjects 3.357 7 0.480

Splints x Sides 9.899 1 9.899 1.98 .202

Splints x Sides x Subjects 35.013 7 5.002

Splints x Intervals 1.155 8 0.144 0.78 .624

Splints x Intervals x Subjects 10.406 56 0.186

Movies x Sides 0.287 1 0.287 1.01 .348

Movies x Sides x Subjects 1.984 7 0.283

Movies x Intervals 2.712 8 0.339 2.10 .051*

Movies x Intervals xSubjects 9.032 56 0.161

Sides x Intervals 0.432 8 0.054 0.86 .558

Sides x Intervals xSubjects 3.527 56 0.063

Splints xllovies x Sides 0.516 1 0.516 0.90 .375

Splints xMovies xSides xSubjects 4.022 7 0.575

Splints xlovies x Intervals 1.086 8 0.136 0.60 .777

Splints xMovies x Intervals x Subjects 12.743 56 0.228

Splints x Sides x Intervals 0.168 8 0.021 0.52 .833

Splints xSides x Intervals xSubjects 2.239 56 0.040

Movies xSides x Intervals 1.099 8 0.137 2.12 .049*

Movies x Sides x Intervals x Subjects 3.635 56 0.065

Splints xflovies x Sides x Intervals 0.338 8 0.042 0.71 .678

Splints x lnvies x Sides x Intervals x Subjects 3.307 56 0.059


Note. Asterisks hiqilight significant p values.











change values for the seventh 40-s interval were significantly

greater than were the values for all other intervals except the eighth.

The 64 EMG change values for the eighth 40-s interval were significantly

greater than were the values for the first, third, fifth, and sixth

intervals. (Experiment-wide average change values for each of the

nine measurements intervals are shown in column five of Table 3-7.)

As can be seen in Table 3-6, the 2 x 2 x 2 x 9 ANOVA within

EMG change scores produced two significant interactions: a two-way

interaction involving movie content x recording interval, and a three-

way interaction involving movie content x side of recording x recording

interval. Of these, the three-way interaction is the more important.

Since the overall two-way interaction involving movie content x side of

recording was nonsignificant (see Table 3-6), the participation of

these two factors in the significant three-way interaction means, in

general, that significant movie content x side of recording interac-

tions do exist for some but not all intervals. A test for simple

movie content x side of recording interactions (Kirk, 1968) was per-

formed at each of the nine recording intervals. Of the nine F values

reflecting simple two-way interactions, three were significant. For

the fifth 40-s recording interval F(1,56) = 2.88, p < .10. For the

seventh recording interval F(1,56) = 3.79, p < .10. For the eighth

interval F(1,56) = 7.12, p < .05. Duncan's comparisons of individual

means within the fifth and eighth intervals produced significant dif-

ferences such that EMGs recorded contralaterally to the splint during

the stressful movies changed more over baseline than did EMGs recorded











Table 3-7.


Means and standard deviations for EMG change scores for
the significant movies sides x intervals interaction
(in pvs)


Ipsilateral Contralateral

Neutral Stressful Neutral Stressful
Interval Movie Movie Movie Movie Average


Average


0.079
(0.49)

0.165
(0.64)

0.160
(0.40)

0.056
(0.58)

0.081
(0.38)

0.093
(0.39)

0.189
(0.44)

0.082
(0.53)

0.154
(0.56)


0.111


0.273
(0.58)

0.346
(0.39)

0.319
(0.52)

0.436
(0.57)

0.357
(0.43)

0.166
(0.37)

0.567
(0.79)

0.745
(0.90)

0.344
(0.53)


0.394


0.475
(0.43)

0.728
(1.40)

0.500
(0.90)

0.621
(1.23)

0.407
(0.73)

0.568
(0.80)

0.880*
(1.24)

0.610
(1.11)

0.679
(1.36)


0.607


0.617
(1.01)

0.749
(0.95)

0.737
(1.12)

0.831
(1.20)

0.972*
(1.37)

0.636
(0.91)

0.983*
(1.02)

0.945**
(0.94)

0.734
(0.79)


0.361


0.498


0.416


0.487


0.455


0.366


0.655


0.596


0.478


0.800


*Indicates significantly
side at the .10 level.

**Indicates significantly
side at the .05 level.


different from neutral movie/ipsilateral


different from neutral movie/ipsilateral





56




ipsilaterally during the neutral movies. Within the seventh interval,

EMGs recorded contralaterally to the splint during both types of

movies changed more over baseline than did EMGs recorded ipsilaterally

during the neutral movies.















CHAPTER FOUR
DISCUSSION


The purpose of the present research was to examine experimen-

tally-the unilateral and interacting effects of occlusal disharmony

and psychological stress on activity in the masseter muscles. Three

prompts for the experiment were methodological shortcomings in research

on the effects of malocclusion on masseteric activity, methodological

shortcomings in research on the effects of stress on masseteric

activity, and the fact that no experiment to date has permitted the

study of how occlusal disharmony factors and stress might interact

to influence masseteric activity. The design of the experiment was

geared both toward redressing the methodological errors or omissions

committed heretofore and toward allowing the variables of occlusal

disharmony and stress to interact in influencing masseteric activity.

The following narrative begins with a discussion of the results concern-

ing experimental validity and with a discussion of future research from

a methodological/procedural perspective. The narrative then continues

with a discussion of the findings concerning masseteric activity and

with a discussion of future research from a substantive point of view.


Data Concerning Experimental Validity

Validity of the Stress Manipulation

One of the recurrent methodological problems in previous

experiments on stress effects vis-a-vis masseteric activity has been











the failure to demonstrate that stress manipulations were indeed

stressful in terms of measurement domains other than EMG. Some

experimenters did not incorporate independent measures of the stressful-

ness of their manipulations (Kydd, 1959; Yemm, 1968, 1969, 1971;

Thomas, Tiber, & Schireson, 1973). Other experimenters did so, but

for the most part found their manipulations to have been not stressful

(Rao & Glaros, 1979; Mercuri, Olson, & Laskin, 1979; Moss & Adams,

1984). The present experiment is clearly an improvement in terms of

having used a demonstrable stress manipulation. As noted in Chapter

Three, exposure to the horrific film content was associated with

greater SCLs and more SCRs than was exposure to the non-stressful film

content and horrific film content uniquely produced greater SCLs and

more SCRs as compared to pre-film baseline recordings. Similarly, a

semantic differential approach to stress measurement, as embodied

in the Anxiety Differential, produced clear differences between horrific

and non-stressful film content. In brief, two domains of stress

measurement and three measures provided convergent validation

(Campbell & Fiske, 1959) that levels of stress were successfully varied

via the film-content manipulation used in the experiment. Hence, it

is arguably reasonable to assert that any observed effects of film

content variations on masseteric EMG activity do reflect effects from

experimental stress.


Validity of the Occlusal Disharmony Manipulation

One of the recurrent methodological problems in previous

experiments on occlusal disharmony effects vis-a-vis masseteric activity











has been the failure to utilize intraoral devices that control

for the possible effects of placing and leaving occlusal interference

in subjects' mouths. As noted earlier, Magnusson and Enbom (1984)

controlled for the effects of placing an occlusal interference into a

subject's mouth, but those investigators did not control for possible

effects of leaving an occlusally inert device in place. To that extent

the non-interference molar clamps used here constitute the first

experimental attempt to control more or less completely for the non-

occlusal effects of receiving and wearing occlusal interference splints.

As such, the present procedure is clearly an improvement over pro-

cedures reported heretofore. However, as noted in Chapter Three, it

fell short of being entirely suitable for the present experimental

purpose. Laboratory assessment of articulator mounted casts bearing

each pair of splints and clinical assessment (and adjustment) of the

splints in each subject's mouth do seem to show that the interference/

non-interference variable was manipulated satisfactorily.

The experiment could have been improved, however, by

incorporating independent judgments vis-a-vis both the laboratory and

the clinical actions of each pair of splints. More importantly, as

noted in Chapter Three, data were obtained that show the non-interfer-

ence splint to have been irritating and painful. The logic of the

present experimental design required that the placebo splint be inert

within the oral cavity. Only a stomatognathically inert appliance can

control for the activities of receiving and wearing an appliance per

se. Insofar as the placebo splints used here were irritating, they











were not stomatognathically inert and, therefore, were not satis-

factory control appliances. Rather, it turned out that both types of

splints amounted to new local dental conditions within subjects'

mouths. Theinterference splint was an irritating dental condition

that involved an occlusal interference. The placebo splint was an

irritating dental condition that did not involve any occlusal interfer-

ence. In brief, the splint manipulation did not entail occlusal inter-

ference versus no stomatognathic impact and did not permit a study of

interactions between stress and occlusal interference of the type

that was intended. Rather, the splint manipulation entailed two

different types of local dental conditions and eventuated in a study

of possible interactions between stress and differing local dental

factors. To that extent, the original purpose of the study was

substantially compromised by the irritation associated with the molar

crowns. On the other hand, the various interactive theories of bruxing

and masseteric hyperactivity (McGlynn, Cassisi, & Diamond, in press;

Ramfjord & Ash, 1983; Rugh & Solberg, 1976) do speak of "local dental

conditions" as being involved in multifactor etiologies. Hence,

experimental variation of the type of local dental condition and the

study of interactions between stress and type of dental condition is

not inconsistent with the general purpose that the experiment was

designed to accomplish.


Future Research from a Procedural Perspective

On the whole, the present experiment succeeded at the level

of convincingly manipulating levels of stress. The combination of











horrific versus idyllic film viewing and electrodermal plus romantic

differential stress assessment is a model for programmatic research

in this area. Of course, stress is a multiform concept with scores

of potential experimental forms. Hence, while continued programmatic

research using the present procedures is justified, such a paradigm

should not stand in the way of utilizing other tactics both at the

level of manipulating stress levels and monitoring the effects of the

manipulation. As noted in Chapter One, various tasks have been used

to manipulate stress in studies on the role of stress in the MPD syndrome

(e.g., Moss & Adams, 1984). Research should continue using such

manipulations provided that they are free of movement artifacts within

masseteric EMG recording and that their receive some credible form of

independent corroboration that they are indeed stressful. Similarly,

various psychophysiological and self-report measures could be used

to monitor the effects of alternative stress manipulations (e.g.,

cardiac and respiratory parameters, state anxiety measures). Research

should continue using these, and other measures of stress-

manipulation impacts in addition to the electodermal and semantic

differential approaches used here. As similar or covergent experi-

mental results are amassed with increasing operational forms of

the experimental stress concept, a more general knowledge base will

have been created. In turn, as divergent experimental results are

produced with different operational versions of the stress concept,

the knowledge base will be more refined.











While the stress manipulation used here was successful, the

occlusal disharmony manipulation was not. A need exists for a stomato-

gnathically inert means of controlling for the effects of receiving

and wearing occlusal interference splints. One way to approach

this problem is to design and fabricate non-interference splints that

are inert, that is, that are not irritating or painful. Magnusson and

Enbom (1984) created balancing-side interference by acid-etching

composite material to the buccal surfaces of molar palatal cusps.

Their control procedure involved simulation of the interference placement

technique using sterile water and not applying composite to tooth

surfaces. As noted, this is an incomplete control procedure in that it

controls for receiving but not for wearing an intraoral device. A

possible approach to the present problem might entail acid-etching

composite materials to produce balancing-side interference then

acid-etching composite material to inter-occlusal spaces to constitute

placebo interference. Of course, it is not yet known whether com-

posite materials etched in interocclusal spaces are irritating.

A second general approach to solving the problem of inert

placebo splints is that of leaving the interference and placebo

splints in subjects' mouths for longer pre-experimental periods.

Quite possibly the irritation produced by the clasps used here

would habituate or adapt after a few days use. Given such an even-

tuality, it would be possible after several pre-experimental days, to

compare the effects of the occlusal interference splint with those of











a pre-experimentally inert placebo appliance. However, this approach

is not without potential problems, such as the potential danger of

splint aspiration over a number of nights use, and possible adjustment

of the masticatory system to the occlusal extension of the interfer-

ence during the pre-experimental period. Obviously, the interference

versus placebo splint manipulation is an area for further research.


Data Concerning Experimental Manipulations

Effects of Stress Manipulation

The ANOVAs performed on both the masseteric EMG change score

data and the masseteric EMG raw score data yielded significant

main effects for movies. Visual examination of the averages showed

clearly that the stressful movies were associated with greater

masseter muscle activity than were the neutral movies. This result

provides support for the theory that bruxism and related muscle

hyperactivity can result from stress. This is particularly true given

the independently corroborating evidence that the horrific movies were

stressful. Of course, other types of stressors are not yet known to

produce the same or similar results. Hence, as noted above, research

would be valuable in which use of a variety of documented stressors

would work toward delineating the empirical boundaries of the

stress/masseteric hyperactivity relationship. As noted in Chapter One,

some previous research has shown similar results with different

stressors. As was noted also though, previous research has been prob-

lematic methodologically. Hence, the approach to stress manipulation










used here, and the approach to independent stress measurement used here,

could serve as to-be-elaborated programmatic research models.


Effects of Splint Manipulation

Neither the ANOVA performed on the masseteric EMG change

score data nor the ANOVA performed on the masseteric EMG raw score

data yielded a significant main effect for the splint manipulation.

This nonsignificant finding was, in part, due to variability between

subjects in response to the splints (i.e., the splintxsubject inter-

action). As noted, laboratory and clinical examinations of the

occlusal effects of the splints showed a satisfactory manipulation of

the occlusal disharmony variable but data from the pain and irritation

questionnaire indicated that the placebo splints were not inert with

respect to non-occlusal factors. Both the interference and placebo

splints were reported to be irritating. Studies have demonstrated

masticatory muscle activity in response to various types of mechanical

and/or electrical stimulation of the teeth and periodontal ligament

in both animals (e.g., Mahan & Anderson, 1970; Thexton, 1968) and

humans (Goldberg, 1971; Hannam, Mathews, & Yemm, 1969). The irritation

caused by the splints in this experiment can be viewed as resulting

from stimulation of the teeth. In turn, the effects of tooth stimula-

tion on masseteric activity might have overridden any corresponding

effect from the occlusal extension.

As noted, one significant result occasioned by the splints was

the main effect for the side of recording. Visual examination of the










masseteric EMG means showed that the side contralateral to both splints

was associated with greater activity than was the side ipsilateral

to them. Since the types of splints used in this experiment were

novel, any interpretation of this result must be guarded. Even so,

since the laboratory and clinical examinations showed differential

splint effects on oral-motor functioning it is interesting and poten-

tially heuritstic to discuss, briefly, how the two types of splints

mediated the effect for side or recording.

Regarding the placebo splints, one hypothesis involves the

notion of tooth sensitivity. According to Dubner, Sessle, and Storey

(1978), when tactile sensitivity of a tooth and its feedback potential

are altered, the pattern of muscle activity will be altered also. For

example, contact on a hypersensitive tooth can elicit an avoidance

reflex protecting that tooth from further damage. For the short time

that the placebo splints were in place in the experiment, they could

have acted to sensitize the teeth to which they were attached, leading

to an avoidance of activity on that side and to relatively low

ipsilateral recordings vis-a-vis masseteric EMG.

Another post hoc explanation of the main effect for side of

recording associated with the placebo splints concerns the activity

of the tongue and the consequence of that activity for contralateral

masseteric activity. Some of the subjects reported informally that

irritation from the splints prompted frequent tongue activity. It

has been shown that tongue activity especially activity in the genio-

glossus muscle, affects TMJ receptors, jaw muscles, and jaw movements











(Ramfjord & Ash, 1983). In order for the tongue to reach the splint

area, the genioglossus muscle would be activated primarily on the

side opposite the splint. This could very well have led to an increase

in contralateral masseter muscle activity and, hence, have contributed

to the main effect for side of recording obtained in this experiment.

Since the interference splint also was irritating, either or

both of the post hoc hypotheses presented above might be relevant also

to the main effect for side of recording associated with the inter-

ference splints. It is possible also that another mediating mechanism

was involved. From their study on the effects of occlusal interference

or mastication, Schaerer, Stallard, and Zander (1967) argue that the

typical muscular reaction to an interference or deflective occlusal

contact is a stop or interruption of contraction activity. This

would hold true for the side which has the interference, but on the

opposite side, by definition, no tooth-to-tooth contact is made. Con-

sequently, contractile activity would not be interrupted on the contra-

lateral side.

Of course, a satisfactory characterization of mediating

mechanisms awaits further experimental work. For the present, it is

possible only to state that the splints acted as significant local

dental factors. The narrative above outlines some of the mechanisms by

which local dental factors are believed to influence masticatory muscle

hyperactivity. In addition, it shows that the main effect for sides of

recording is not wholly inexplicable.











Movie ContentxSide of Recording xRecording Interval

Even though the interaction between type of splint and movie

content was nonsignificant, as noted in Chapter Three, two interactions

were significant. Of these two, the interaction of movie contentxside

of recordingxrecording interval is the more important. Analyses of

simple two-way interactions at each of the nine intervals showed

significant interactions of movie content and side of recording at the

fifth, seventh, and eighth intervals. Insofar as the effect for side

of recording reflects the operations of local dental factors, this

result indicates that the experiment produced what might be called a

"stress x local dental factors interaction" at three of the nine

recording intervals. Although this interaction did not involve occlusal

disharmony per se, it is consistent with multifactor interaction theories

in general. Notwithstanding the popularity of multifactor interaction

thinking (Alling & Mahan, in press; McGlynn, Cassisi, & Diamond, in

press; Ramfjord & Ash, 1983; Rugh & Solberg, 1976) the present result

constitutes the first experimental demonstration with human subjects

that psychological and local dental factors can interact to influence

masticatory muscle action. As such, it calls for continued and

programmatic research on diverse multifactor interactions making use

of methodological tactics and elaborations such as those described

previously.


Future Research from a Substantive Perspective

As noted, stress is a multiform concept that can be represented

experimentally with a variety of independent and dependent variables.









The manipulation of film content was successful in this experiment

because it influenced differentially some orthodox measures of stress

as well as the masseteric activity measure. Nevertheless, a single

approach to producing experimental stress is inadequate given the

diverse usage of the concept in the literature. Consequently, the

success of the stress manipulation in this experiment should serve

primarily to encourage further experimental research on stress as a

factor in masseteric activity. The first goal of such programmatic

experimental research would be the identification of stressors that

do and that do not affect mandibular muscle function. The ultimate

goal of such research would be the articulation of basic principles

useful in the diagnosis and treatment of facial pain sufferers.

Stressors which could be used in methodologically sophisticated experi-

ments include intense cognitive tasks, personally frustrating tasks,

manually complex or undesirable tasks, movie watching tasks, tasks

involving the anticipation of unpleasant experiences, and so forth (cf.

Rao & Glaros, 1979; Thomas, Tiber, & Schireson, 1973).

In the general experimental paradigm used here it was important

that a non-stressful task be included so as to document the stressful

nature of the horrific film. Experiments following this paradigm but

using other stress manipulations should also incorporate similar

but non-stressful tasks. For example, in using cognitive activity as

a means of stress manipulation (e.g., Moss & Adams, 1984) subjects

might be asked to perform very simple as well as very complex mathe-

matical problems. For another example, in using discriminated button

pressing as a means of stress manipulation (Yemm, 1971), subjects might

be asked to respond to a very slow as well as a very fast series of lights.











An alternative general experimental approach is known as

the parametric study. In parametric experiments, in general, levels of

an independent variable are systematically altered, but it is not

necessary that any experimental procedure represent a zero value

of the independent variable. In the present context, a parametric

study would not require any experimental task to be completely non-

stressful. Rather, it would require that differing levels or differing

amounts of stress be represented experimentally. Stress manipulations

such as those used by Moss and Adams (1984) and by Yemm (1971) lend

themselves readily to a parametric approach and the approach itself

avoids the problem of incorporating entirely non-stressful experimental

tasks. The only major constraint on experimental-task selection within

a parametric strategy in the present context is that the various

tasks not require movement of the head, face, or upper body. This

restriction, of course, is shared by the stress versus non-stress

approach used in the present experiment.

Although the knowledge base concerning the effects of various

stress manipulations is limited, it is in an advanced state relative

to the knowledge base concerning the effects of various occlusal dis-

harmony manipulations. As noted, from a procedural perspective,

the present experiment could have been improved by using an inert

placebo splint and some potential means were presented for achieving

this goal. However, it might turn out that no approach exists that

will afford satisfactory control over the non-occlusal effects of

receiving and wearing occlusal interference splints. Here, again,










parametric research tactics might serve to circumvent the methodologi-

cal problem. For example, informative comparisons of the effects of

different types of interference can be made in the absence of placebo

devices. Balancing side interference, working side interference

and retruded contact position interference have all been discussed

in connection with mandibular muscle dysfunction (Carlsson & Droukas,

1984). These interference can be fabricated and studied comparatively

in the absence of inert control appliance. For another example, informa-

tive comparisons could be made of the effects of single versus multiple

interference. The number of occlusal interference present in a

patient's mouth has been implicated as a potentially important variable

in mandibular muscle dysfunction (Ramfjord & Ash, 1983). This variable

obviously lends itself readily to parametric experimental work. As

a third example of parametric thinking, informative evaluations can be

made of different widths, thicknesses, and degrees of incline of one

or more types of interference. As noted in Chapter One, some work

along these lines has been done (Bakke & Moller, 1980). It could be

incorporated though, into relatively more sophisticated experiments.

In a general sense, meaningful information can be obtained without

placebo appliances by using multiple-site EMG recordings and multiple-

site pain and irritation questionnaires. For example, a methodologi-

cally sound experiment could be designed in which the effects, on both

masseter and pterygoid muscles, of 0.25, 0.50, 0.75, and 1.00 mm thick

balancing side interference and working side interference are com-

pared. The logic behind this approach requires no zero values of any

variable, that is, no inert appliance.











What have been described above are procedural and design

options for programmatic research evaluating the effects of experi-

mental stressors on masticatory muscle activity and the effects of

experimentally produced occlusal disharmonies on masticatory muscle

activity. These research options can and should be combined for the

assessment of multifactorial theories. Since multifactorial/interactive

theories are no doubt accurate in a very general sense and since the

designs of multifactorial experiments typically include unilateral

conditions as well, multifactorial experiments should be conducted as

a matter of course, to flesh out the multifactor view. At present,

virtually no trustworthy information is available as to what effects

different kinds of stressors have when combined with different types

of interference, for different lengths of time, and so forth. This

type of information is necessary if the data from experiments are going

to be of any significant value to clinicians whose patients are

suffering from facial pain. Owing to the paucity of methodologically

sound multifactor experiments virtually all specific research problems

are open to systematic experimental work of the type undertaken and

discussed here.

































APPENDICES















APPENDIX A
DESIGN OF OCCLUSAL INTERFERENCE
AND PLACEBO SPLINTS


Type A Top View


Type B Top View


Sideview


Note. Type A = interference splint; Type B = placebo splint















APPENDIX B
PAIN AND IRRITATION QUESTIONNAIRE


I. Pain:


Rating


II. Local Irritation:


Rating


At the times specified below, rate on a scale of

0-10 the amount, if any, of pain and/or fatigue

you have had in your facial and/or jaw muscles


A. Before fitting of appliance

B. Maximum during the evening when the appliance

was in your mouth

C. 19 hours after fitting of appliance

D. 2 hours after removal of appliance

E. 24 hours afer removal of appliance


At the times specified below, rate on a scale of

0-10 the amount, if any, of irritation with your

teeth and/or gums in the area around which the

appliance is/was attached


A. Before fitting of appliance

B. Maximum during the evening when the appliance

was in your mouth

C. 19 hours after fitting of appliance

D. 2 hours after removal of appliance

E. 24 hours after removal of appliance















APPENDIX C
TESTING ORDER FOR SUBJECTS


CODE: T = Testing Session
I = Interference Crown/Splint
P = Placebo Crown/Splint


Subject #1
T(1)
T(2)


Neutral Film #1
Neutral Film #2
Stressful Film #1
Stressful Film #2


Subject #2
T(l.) P
T(2) I

Subject #3
T(T.) I
T(2) P

Subject #4
T(.l) P
T(2) I

Subject #5
T() I
T(2) P

Subject #6
T() P
T(2) I


Subject #7
T(1)
T(2)


Subject #8
T(1.) P
T(2) I
































APPENDIX D
ADDITIONAL DATA TABLES















C)0 0 M- C C) M CD -
0 n On 0 0 en 0 i-






C 0
S- -- 0 C) CD -











CD 0 0- CO O) -.0 0 CCO 0
LL .







c4)



oD,
> D oj co m co oj t. C" O
*0 cn O n r- co r-









>- ::- F- 0 0 .0 0- ( -- -
,E C O -
























0 W co
r 0 ~ O
Ec











.-0 -O.: t t
., o C c cn co cM u- r. c



o) .
mc C) cd Zd- i- (- i- CD -D -



CDC

c m


4,O) 0 r -zi 00 m ko .0
o F-- C) C C C C


tA
o- 0 n U) C C) 1c ) vo k. -

(1) ui 0 0- C') m F- C) C) F-


C)
.a wo 1


4-))

C) 4-
-O 01 -. c. c. c-.


(0( C- CtO CO O U) r to Ln c U


(- C) CO- 0O tO ui- CO^ to U) (

o C') (N C- n]i- F- F- C) C

Ue) -c



O O o C dt ci io CO to to
0)0 F i- rP CO hi Cr) CO CO i- o



CU) U) r u u3 CO CO CO m CO d F- C-



I- I-.



in I C <- r-
t/i>~-


Q n3
>I11
Iu H c o -- in u ^ o c














OD Ci U) c r- mO O CM


co = f
C:) m 0 0 0 0 0 0)
r r--: r -O Z
C O U) CMO \i -O O0 0 C Or-




Sr--









'O

E 00

S-'C
S- C C) )Ii NC C ) r- ) U ) C D )









1> j o O N n N N
j3C> -: tD o l CDj co o C O CLn m




















Sa)
0U 0 0 0 0 0 0 0 0
^.0 CO 0i CM U) CO U) CM U) U)




























SO C) Cr- C)


o a
c -C
0 0)
m-> C o oD CM C CMd CM al
U-) 0 IZ) C" LO m co L n C')

Eo c o o o o o














CCo
co
4--) 0 Ln qn 0 i-n 00 i- oT CD



z o oC r o r- d o or

m1 > ) C O r-D r- 0" r'





















0 C D C m ) 0 D
I- CI
i0 C C6 0 ) s- CM CM C')
Ca r m00 0 0 o 0 0 0 0





t *-
cc I o co d- 0) CM U) CO CM 0

toto N. U) U) U- N- U) U) U) U)
0 C


(r 4-'















(0 E= -



to CQ














ja) +->C
(0 I C:
I- H-


















S-0




E---







4U C
0















0
o


4- c






4-)
O)



0) 0)

c* 0
S--





S- O0


0







0




E W
0I

O
4- o
4-)

















4 o














4;I
-0 0
.- -
> 43


U)
.c:
0. (D






0








4-
0

U )
c! 0

4--

-0


03 U




LU





S-,



(0(0
43


-
C0

(U







U
c
) r-

4--

a) C)

0.c.
c4-










t--
4a

U)




a)






a) 4Q
4---


r- CM c UO n o0 Nr Co


* r- Cfl On


0 0 0 0









00 0'
C) C) c; C)

.tz mo LO CMJ
C) m k0 C"






- o on CM\












































O t 0 CO
CM ,- CM

00o C C) )












C\ Om O
CM 0 i' -




cj CM o CD

c- CM C;-


--- r -

CM i- o-

- co C '0
CMN Mt o Uo

CM CM. 0




11- r-. o- Lo
CM t- 0' '.0














c( C0 (Y) rN-
CD 10 C:) 00



-i r I'D (M
M- CO -C3







CM r- CM
00 0) C0) CM


- i- co
r- r N- Ln

,- ) C') N-


I) I'- CM '.0
0- 0 0 0
- o C) o



SC0 0C C






O O
o o o oa
















o o O o
C- ) 0 0C 0









c.- 0I O












o r) o c,
























r- ::- Ci
C- C) c c;
0- CM 0 O















- LO N-


4-J

3
*i*) u











Table D-4.


Means and standard deviations computed over nine intervals
for SCL change scores from baseline for each of the 8
subjects, groupedby four movies (in pmhos)


Stressful Movies Neutral Movies

Dawn of
Subject # the Dead Psycho II J.L.S. I J.L.S. II

1 10.64 (1.40) 8.21 (1.75) 8.68 (1.09) 3.47 (0.45)

2 6.13 (1.07) 5.04 (4.24) -0.77 (0.89) -6.35 (0.94)

3 5.79 (0.70) 5.34 (1.59) 3.26 (0.34) 0.29 (0.17)

4 13.42 (0.48) 10.66 (1.92) 2.37 (2.11) 2.60 (1.09)

5 8.05 (1.27) 14.83 (3.00) 2.61 (0.76) 0.93 (0.26)

6 13.15 (1.82) 14.51 (2.07) 4.28 (3.17) 8.61 (2.18)

7 5.58 (2.09) 19.08 (4.97) 0.24 (1.26) 11.38 (3.43)

8 0.21 (0.17) 1.21 (1.17) -0.05 (0.02) 0.08 (0.04)


Note. J.L.S. I represents the first Jonathan Livingston Seagull film
clip; J.L.S. II represents the second Jonathan Livingston Seagull
film clip.












Means and standard deviations computed over nine intervals


for SCL raw scores for each of the 8 subjects
four movies (in pmhos)


grouped by


Stressful Movies Neutral Movies

Dawn of
Subject # the Dead Psycho II J.L.S. I J.L.S. II

1 22.35 (2.16) 13.42 (2.15) 20.39 (1.77) 8.67 (0.60)

2 15.30 (1.38) 22.01 (4.95) 8.40 (0.93) 10.62 (1.12)

3 9.49 (0.93) 7.20 (1.64) 6.96 (0.40) 2.15 (0.19)

4 30.93 (2.13) 18.08 (2.53) 19.87 (2.14) 10.02 (1.34)

5 11.94 (1.53) 19.23 (3.57) 6.50 (0.79) 5.33 (0.29)

6 22.30 (2.77) 17.65 (2.64) 13.42 (3.34) 12.75 (2.33)

7 15.24 (2.32) 30.63 (5.77) 9.90 (1.28) 22.93 (3.76)

8 1.73 (0.17) 5.00 (1.27) 1.47 (0.03) 3.87 (0.04)


Note. J.L.S. I represents the first Jonathan
clip; J.L.S. II represents the second
film clip.


Livingston Seagull film
Jonathan Livingston Seaqull


Table D-5.


















cr
0




>1








S.-



U)
co












4-


0)
a)
S-
o





4-





'4-
0

0








4-
")




.-
0

















: )
r0
O -










'-
u




0)
ct













4-0
-o
















1----

0)





h-o-




H0
ct


F --







4-,
S-)










>
0










4-














a4


0) 0




0 L


C\J
c
0
U)
),







0








0)
C)-


m C CD C r C o oC
0 o C\ o














r- 0 f C'Y) 0-> ) 0O -
-- a- O- Zj- -






















C r- C C CD C) CD














om 0 CD ro C CD Co
























I- (Cj o 1 U) k0o rN 0oo


70
c
0
U
()

0)
4-)
o"1
4-,
c
0

U)
0
S-

0)















0
-D





E





o



0






r0
Ca





o
0




4-





*r-



(0U
* (U
J Cv












a)
+->



s- i
*I f
4-
CD














Table D-7.


The level of self-reported anxiety based upon the Anxiety
Differential for each of the 8 subjects, grouped by four
movies


Stressful Movies Neutral Movies

Dawn of
Subject # the Dead Psycho II J.L.S. I J.L.S. II

1 61 23 30 25

2 84 82 48 56

3 58 66 42 47

4 60 76 57 55

5 91 83 50 48

6 89 89 42 37

7 95 92 64 60

8 109 90 38 31


Note. J.L.S. I represents the first Jonathan Livingston Seagull film
clip; J.L.S. II represents the second Jonathan Livingston Seagull
film clip.
















Table D-8.


The self-report ratings of pain and local irritation
based upon the pain and irritation questionnaire, for
each of the 8 subjects, grouped, by splint condition


Pain Local Irritation

Interference Placebo Interference Placebo
Subject # Splint Splint Splint Splint

1 2 0 0 0

2 0 0 18 12

3 0 5 12 7

4 0 0 0 0

5 3 0 8 1

6 3 1 0 4

7 0 0 8 10

8 6 0 5 2













Table 0-9.


Means and standard deviations for EMGI change scores from
baseline grouped by movie and splint conditions (in ivs)


Stressful Neutral
Movie Movie Average

0.444 0.085 0.265
Interference splint
(0.55) (0.35) (0.50)


0.343 0.137 0.240
Placebo splint
(0.44) (0.52) (0.49)

0.394 0.111
Average
(0.50) (0.44)




Table D-10. Means and standard deviations for EMGC change scores from
baseline, grouped by movie and splint conditions (in pvs)


Stressful Neutral
Movie Movie Average

0.529 0.378 0.453
Interference splint
(0.55) (0.63) (0.59)


1.072 0.836 0.954
Placebo splint
(1.22) (1.31) (1.27)


0.800 0.607
Average
(0.98) (1.05)










Table D-11. Means and standard deviations for EMGI raw scores grouped
by movie and splint conditions (in pvs)


Stressful Neutral
Movie Movie Average

1.563 1.204 1.384
Interference splint
(0.59) (0.35) (0.52)


1.629 1.423 1.526
Placebo splint
(0.82) (0.82) (0.83)
------- ------------------------------I
1.596 1.314
Average
(0.72) (0.64)


Table D-12. Means and standard deviations for EMGC raw scores grouped by
movie and splint conditions (in jvs)


Stressful Neutral
Movie Movie Average

2.007 1.843 1.925
Interference splint
(1.59) (1.92) (1.79)


Placebo splint 2.586 2.350 2.468
Placebo splint
(1.61) (1.70) (1.66)


2.297 2.097
Average
(1.63) (1.83)














Table D-13.


Means and standard deviations for EMG change scores grouped
by movie and splint condition (in pvs)


Stressful
Movie


Neutral
Movie


0.487 0.232
Interference splint
(0.55) (0.53)


0.708 0.487
Placebo splint
(0.87) (0.93)







Table D-14. Means and standard deviations for EMG raw scores grouped
by movie and splint conditions (in lvs)


Stressful Neutral
Movie Movie

1.785 1.524
Interference splint
(1.11) (1.15)


2.108 1.887
Placebo splint
(1.22) (1.26)


__








Table 0-15. Means and standard deviations computed over nine intervals
for EMGI change scores from baseline grouped by condition
and subject (in pvs)

Subject # Interference Splint Placebo Splint

Stressful Movie
1 0.466 (0.22) -0.471 (0.33)
2 -0.189 (0.18) 0.952 (0.41)
3 -0.099 (0.25) 0.572 (0.38)
4 0.642 (0.60) 0.010 (0.10)
5 1.705'(0.78) 0.484 (0.55)
6 0.145'(0.11) 0.107 (0.07)
7 0.312 (0.08) 0.883 (0.12)

8 0.570 (0.31) 0.205 (0.10)

Neutral Movie
1 0.227 (0.11) -0.524 (0.45)
2 -0.025 (0.16) 0.510 (0.36)
3 -0.267 (0.29) 0.373 (0.32)
4 -0.378 (0.18) -0.035 (0.15)
5 0.709 (0.17) -0.419 (0.07)
6 -0.222 (0.35) -0.018 (0.07)
7 0.292 (0.09) 1.207 (0.22)
8 0.342 (0.11) -0.003 (0.06)









Table D-E1. Means and standard deviations computed over nine intervals
for EMGC change scores from baseline grouped by condition
and subject (in pvs)

Subject # Interference Splint Placebo Splint

Stressful Movie

1 1.141 (0.45) 0.342 (0.20)
2 -0.396 (0.30) 3.606 (0.56)
3 0.247 (0.18) 0.593 (0.48)
4 0.222 (0.19) 0.523 (0.78)
5 1.435 (0.37) 0.490 (0.38)
6 0.166 (0.05) 0.364 (0.21)
7 0.675 (0.14) 2.498 (0.46)
8 0.736 (0.41) 0.057 (0.24)

Neutral Movie

1 1.865 (0.72) 0.472 (0.27)
2 0.104 (0.48) 3.536 (0.72)
3 -0.320 (0.19) 0.720 (0.46)
4 -0.031 (0.09) -0.204 (0.26)
5 0.459 (0.15) -0.180 (0.14)
6 0.171 (0.15) -0.026 (0.08)
7 0.648 (0.07) 2.440 (0.53)
8 0.128 (0.29) -0.073 (0.08)











Table D-17. Means and standard deviations computed over nine intervals
for EMGI raw data grouped by condition and subject (in pvs)

Subject # Interference Splint Placebo Splint

Stressful Movie

1 1.836 (0.41) 1.748 (0.63)
2 0.981 (0.25) 3.432 (0.73)
3 1.551 (0.45) 1.602 (0.60)
4 1.892 (0.71) 0.570 (0.18)
5 2.835 (1.16) 1.574 (0.68)
6 1.405 (0.15) 0.657 (0.09)
7 0.992 (0.12) 1.923 (0.19)
8 1.010 (0.42) 1.525 (0.17)

Neutral Movie

1 1.597 (0.30) 1.695 (0.91)
2 1.145 (0.42) 2.990 (0.56)
3 1.384 (0.52) 1.403 (0.58)
4 0.872 (0.32) 0.525 (0.24)
5 1.839 (0.26) 0.671 (0.16)
6 1.038 (0.47) 0.532 (0.09)
7 0.972 (0.14) 2.247 (0.34)
8 0.781 (0.15) 1.323 (0.10)




Full Text
xml version 1.0 encoding UTF-8
REPORT xmlns http:www.fcla.edudlsmddaitss xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.fcla.edudlsmddaitssdaitssReport.xsd
INGEST IEID EE98Z9ZZY_DHSSAG INGEST_TIME 2012-02-29T18:24:33Z PACKAGE AA00009144_00001
AGREEMENT_INFO ACCOUNT UF PROJECT UFDC
FILES