Perception Jaw position

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Perception of Jaw Position
During Different Conditions
The perception of jaw position, measured as the ability lo
produce a predetermined mandibular posture repetitively, was
recorded under different experimental conditions. A control group
of asymptomatic subjects was tested before and after anesthesia
of the TMJs and after fatigue of the masticatory muscles. Groups
of patients with craniomandibular disorders of arthrogenic or
myogenic origin were also tested. None of the experimental
variables affected position perception, and the patient groups did
not differ from each other or the normal group in perception of
jaw position. The possible clinical value of such recordings in
differential diagnosis is therefore open to question.
(J CRANIOMANDIB DISORD FACIAL ORAL PAIN 1989;3: 147-151.)
Mandibular kinesthesia iscontrolled by different
receptors, including those in
the temporomandibular joints
(TMJs) and masticatory muscles.
Different methods have been
used to elucidate this sense, eg,
testing of the ability to produce a
predetermined mandibular pos-
ture repetitively' or compare the
size of different gauges placed be-
tween the teeth.'
Various experimental proce-
dures have been found to alter
proprioceptive sense. Injection
of a local anesthetic into the
TMJ capsule of healthy subjects
caused significant deterioration
in the appreciation of mandibu-
lar position' and decreased motor
control of jaw movement.^ After
bilateral blocking of the lateral
pterygoid muscles in healthy sub-jects, the accuracy of repetitively
produced mandibular postures
was found to decrease signifi-
cantly."" In subjects who devel-
oped fatigue in the jaw muscles
subsequent to muscular work,
mandibular kinestbcsia was im-
paired significantly.' Experi-
mentally induced jaw muscle
fatigue did not alter thickness
discrimination in normal suh-jects, however,* '^ while a signifi-
cantly impaired discrimination
ability was found for subjects
with symptoms of myofascial
pain.'
In craniomandibular disorder(CMD) patienls, the positional
sense was found to be poorer in
those with arthrogenic etiology
than in normal subjects and pa-
tients with symptoms of my-
ogenic origin.*^ Loss of directional
control of the mandible has been
associated with disk displace-
ment. Tissue damage of the pos-
terior attachment after a per-
manently displaced disk, and not
TMJ problems in general, was
supposed to explain the impaired
directional orientation control.'
The relative contribution of dif-
ferent sensors to mandibular kin-
esthesia thus seems uncertain. A
different kinesthetic ability in
subgroups of patients with CMD
could, however, be of possible
Urs Dahlslrom, LDS, Odonf Dr
Associate Professor
Department of Slotnalogtialhic
Physiology
Torgny Haraldson, LDS, Odont Dr
Associate Professor
Department of Stomatognathic
Physiology
Cunnar E. Carlsson, LDS, Odont Dr
Professor and Chairman
Department of Prosthetic Dentistry
Faculty of Odontology
Universily of Götehorg
Box 33070
S-400 33 Cotehorg, Sweden
Journal of
Craniomandibular Disorders:
Facial & Oral Pain 147
Dahlstrom
clinical value in differential di-
agnosis. This would imply that a
relatively simple diagnostic mo-
dality might be available, but
this would be dependent on fur-
ther investigation before it could
be recommended for differentia-
tion of CMD patients.
The purpose of this study was
first to evaluate mandibular po-
sition sense in normal subjects
before and alter anestbesia of the
TMJ capsule, and also after jaw
muscle fatigue. Subsequent to
this evaluation, a comparison
would be made with patients
having CMD of myogenic and ar-
throgenic origin.
Materials and Methods
Subjects
Three groups were tested on
their ability to produce predeter-
mined mandibular postures re-
petitively. All subjects gave in-
formed consent prior to par-
ticipation. The normal group,
healthy volunteers from the staff
at the Department of Stomato-
gnathic Physiology, University of
Göteborg, comprised three males
and two females, aged 27 to 42
years (mean 34 years), and they
were tested under three condi-
tions. The two other groups con-
sisted of symptomatic patients,
referred for diagnosis and treat-
ment of CMD. One of the groups
comprised ten female patients,
aged 18 to 78 years (mean 38
years), with signs and symptoms
of intracapsular TMJ dysfunction
such as tenderness, crepitus, or
locking. This constituted the TMJ
group.
The third group, four males
and six females aged 24 to 49
years (mean 34 years), had signs
and symptoms emanating from
the jaw closing muscles of sup-
posed neuromuscular origin, and
they were called the muscular
group. There were no signs and
symptoms of intracapsular in-
volvement in this third group,
whiie some of the patients in the
TMJ group also had jaw muscle
tenderness.
Procedure
The method used to measure
mandibular kinesthcsia has been
described by Thilander.' The sub-
jects were seated upright in a
dental chair with their head sup-
ported on a neck rest. They were
asked to lower the mandible to an
arbitrary position and to memo-
rize the chosen opening position
for 10 seconds. The subjects were
then required to ñnd the chosen
position, in less than 5 seconds,
ten times in close succession with
tooth contact between each at-
tempt. The distance between the
maxillary and mandibular cen-
tral incisors was registered by
means of a vernier calibrated
in millimeters. Two recordings
were performed, one with a small
opening (about 10 mm between
the incisai edges) and one with a
wide opening (about 25 mm).
The subjects performed several
preliminary tests for familiariza-
tion with the procedures. They
were not informed of their re-
sults. The 20 patients performed
the double tests before any treat-
ment of their symptoms.
The five healthy subjects made
the same estimations under two
more conditions: (!) after stren-
uous activity and fatigue of the
jaw muscles and (2) after anes-
thesia of the TMJs. The muscular
fatigue was created by having
the subject clench on a force
transducer placed between the
premolars or molars. After es-
tablishing the maximal force,
the subjects were instructed to
clench at 30% of tbe maximal
force level as long as possible,
with visual feedback of the force
all the time. This was immedi-
ately followed by the two test se-
ries. Following these recordings,
the tests were carried out a third
time on the healthy volunteers af-
ter injection of 0.2 mL anesthetic
(f% Xylocain) into the TMJ cap-
sule bilaterally. The double tests
were performed within 10 min-
utes after the last injection.
There were several weeks be-
tween each of the three experi-
mental conditions. For each
series of ten record) n^i, the de-
viation from or coincidence with
the chosen position was taken to
represent the positional sense.
Student's í test, Mann-Whit-
ney, and Wikoxon tests were ap-
plied to compare the different
groups and experimental condi-
tions. Probability levels below
5% were accepted as statistically
significant.
Results
The mean maximal mouth
opening for the healthy volun-
teers was 54 mm (range 51 to Ó3
mm). The average maximal force
produced when clenching on
the force transducer was 550 N
(range 450 to 700 N) and the time
to fatigue at the 30% level was a
mean of 144 seconds (range 72 to
240 seconds).
The ten patients in the TMJ
group had a mean maximal
mouth opening of 33.9 mm (range
20 to 50 mm). Two had A, I, two
had D¡ II, and the rest A, II and D¡
III, according to the Helkimo dys-
function indices.'" The ten pa-
tients in the muscular group had
a mean maximal opening of 46.5
mm (range 38 to 62 mm). Half of
the group had A, I and half A, 11.
Seven had D, II, the rest D, III.
The average values for the cho-
sen positions (small and wide, re-
spectively)for the normal group
under the three experimental
conditions and for the TMJ and
muscular groups are shown in
Table 1. The distributions of de-
viations (positive or negative)
from the chosen positions for the
groups are shown in Fig I. There
were no significant differences in
deviation from the chosen posi-
tions between any of the three ex-
perimental conditions in the nor-
mal group for hoth estimations.
Similarly, there were no signifi-
cant differences between the two
groups of patients for each series
of tests or between any of the
patient groups and the normal
group (Fig 1). The distributions
of deviations between small and
wide opening did not differ dur-
ing any experimental condition
146 Volume 3, Number 3, 1989
Dahlström
in the normal group or any of the
patient groups. The percentage
distributions of overestimation,
underestimation, or coincidence
with the arbitrary chosen posi-
tions are shown in Table 2.
Discussion
The intention of this study was
to elucidate mandibular position
perception, measured as the abil-
ity to produce a predetermined
mandibular posture repetitively
during different conditions. Sim-
ple tests to differentiate a pre-
dominantly arthrogenic or my-
ogenic etiology would obviously
be of value since the difficulties
in the clinic may be considerable.
This dilemma may have a bear-
ing on the results obtained, ic, no
difference in jaw perception be-
tween the groups.
The average deviation from the
chosen positions for the normal
group seems to be in accordance
with earlier findings."'^ A greater
rate of overestimation has been
observed before^ and was found
also in this study.
Two degrees of mouth opening
were tested during each condi-
tion since the behavior of the
receptors may vary with the in-
termaxillary distance. Morimoto
et al" found that the oral discrim-
ination ability tended to decrease
with the degree of mouth opening
and that the position sense may
be involved in the discrimination
ability.'^
Though there were no statisti-
cally significant differences in the
deviations between small and
wide opening, the position sense
was, with one exception, always
less accurate at wide opening, es-
pecially in the muscular group
(P = 0.06). The results do not
contradict the assumption that
the behavior of the receptors var-
ies with the vertical dimension.
Prolonged activity in the mas-
ticatory muscles did not change
the position perception in this
study. On the other hand, it has
been reported that the postural
position of the mandible changed
(interocclusal distance increased)
Table 1 Average Positions (and range) in mm Between the
Incisai Edges During Small and Wide Opening in the
Normal Group Under the Three Experimental Conditions,
the TMJ Group, and the Muscular Group
Normal group (N
Before
experiments
s 8.6 (8-10)
w 28.0 (20-40)
After
anesthesia
10,4 (8-12)
28.4 (20-39)
= 5)
After
fatigue
11.0 (10-12)
2a.8 (21-36)
Patients
TMJ group
(N = 10)
11.4 (5-12)
22.1 (19-31)
Muscular group
(N = 10)
8.6
23.7
(5-12)
(16-30)
NORMAL
6
5
4
3 •
2 -
1 •
0 -
BEFORE
EXPERI-
MENTS
AFTER
ANAES-
THESIA
AFTER
FATIGUE
PATIENTS
TMJ MUSCULAR
GROUP GROUP © - SMALL OPENING (i<)
• = WIDE OPENING (x)
Fig 1 Distribution of means (x) ±1 standard deviation from ten recordings of
deviations from the chosen position in the normal (N = 5), TMJ IN = 10), and
mitícular {N = 10) groups during .small and wide opening.
after a prolonged mouth opening
and after a long period (30 min-
utes) of intense chewing.'""'
The muscular work performed
by the normal subjects in this
study falls far below that of the
subjects in the study of Christen-
sen.^ In his study, subjects who
developed fatigue had an im-
paired position sense, while suh-
jects who did not develop fatigue
even after strenuous muscular
work had not. Sustained isomet-
ric clenching, similar to that used
in the present study, was re-
ported not to alter the thickness
discrimination ability in normal
or MPD subjects.' Nor did the po-
sition sense of the muscular
group in this study differ from
that of asymptomatic subjects.
This result is in accord with ear-
lier findings,* while others have
found a reduced discrimination
ability in MPD patients.' There is
evidence that muscle afférents
lournal of Craniomandibular Disorders: Facial & Oral Pain 149
Dahlstrom
Table 2 Mean Percentage Distribution of Overestimation,
Underestimation, and Coincidence with the Arbitrary
Position In the Two Series in the Normal Group, the TM)
Croup, and the Muscular Croup
Normal group (N - 5] Patients
Before After After TMI group Muscular group
experiment anesthesia fatigue (N = 10) (N = 10)
Overshooting
Undershooting
Coincidence
78
48
16
18
6
34
70
62
14
20
16
18
M
68
16
18
20
10
s = small opening.
Table 3 Number of Subjects in the Three Groups with an
Average Deviation of More or Less than 2 and 4 mm from
the Chosen Positions in Small Opening
Average
deviation
¡mm) Normal group TM] group
Muscular
group
<4
are important in sensing jaw po-
sition,'-^ but this ability was not
affected by fatigue or symptoms
from the masticatory muscles in
the present study.
Receptors in the TMJ, which
mediate the position sense, are
predominantly located laterally
and lateroposleriorly in the cap-
sule and lateral ligament.' Block-
ing of these receptors has heen
shown to produce deterioration
in mandibular perception.'" In
the present study, however, in-
jection of a local anesthetic lat-
erally into the TMJ capsule did
not significantiy distort the abil-
ity to produce a predetermined
mandibular posture. This obser-
vation is supported by findings of
previous studies related to the ef-
fect of TMJ anesthesia on the pos-
tural position'* and the move-
ment area of the mandible,"
except for an inereased maximal
mouth opening assumed to be
due to an impaired protective re-
flex mechanism.
Anesthesia of the joints has
also been found to have no effect
on the oral discrimination abil-
ity.''^ '" The position sense in the
group of subjects with intracap-
sular dysfunction did not differ
from that in normal subjects, a
result thai again deviates from
some earlier findings.*
These results, taken together,
seem to support the •. ' nclusion
that joint receptors '.. v: riot essen-
tial for position perception of the
mandible. This is not to say that
mechanoreceptortí in the joint
capsule are not determinants of
jaw position. The capacity of
central regulatory mechanisms,
based on cortical awareness,
could rapidly call into play other
receptor systems to act in a com-
pensatory manner and maintain
jaw position perception.
If a certain average deviation
from the chosen position, eg ±2
or 4 mm, is taken as a positive
result of a jaw perception test
(Table 3), the diagnostic sen-
.sitivity'^ in identifying arthro-
genous or myogenous patients is
not acceptable. The ±4 mm limit
seems to be too wide, as it in-
cludes most healtby subjects as
well as patients.
In summary, none of the ex-
perimental variables affected the
position sense, as measured in
this study. Neither was any di-
vergent perception o£ jaw posi-
tion recorded in any of the
suhgroups of patients with CMD
of different origin. Therefore, the
possihle clinical use of such a test
for differential diagnosis of CMD
seems not to be warranted, as
both sensitivity and specificity
are unacceptable. D
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