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41
Introduction
The accuracy of limb movement is improved
by visual feedback. There are two types
of visual feedback available for tracking
performance of limb muscles: one is the
visual feedback of the target, the other is
the direct visual feedback of the moving limb
itself. Motor control of jaw muscles is less
developed than that of limb muscles during
isometric contraction, when the target force
level was presented by means of visual
feedback.
For the jaw, evidently only the former
applies. (Van Steenberghe et al.,1991)
1
.
Unlike limbs, as one can not see one’s
own jaw, it explains the poor performance,
thus visual cues seemed unimportant for
obtaining accurate jaw position while the
head was kept immobile (Reinhilde Jacobs
et al.,1992)
2
.
However, It seems reasonable to believe
that neither visual feedback nor verbal and
manual practicing can achieve a significant
extension of border movement (Jou-Song
Wang and Yuh-Yuan Shiau, 1987)
3
.
The velocity of mandibular movement is
affected by lots of factors which can be
influenced by clenching, food stuff in mouth
and activity of mastication muscles. In
general, it was found that it ranged from
50 mm to 200 mm per second in a group
of normal subjects and varies widely from
person to person. Jaw muscle could be
control by a variety of central regions
i nc l ud i ng t he cerebe l l um, amygda l a ,
thesomato-sensory or orb i ta l area of
cerebral cortex (Sessle,1977)
4
, In voluntary
jaw movements and precise control of
mastication, we can find out the connections
between precentral cortex and afferent
muscle feedback (Luschei and Goodwin,
1975
5
; Hoffman and Luschei, 1980)
6
.
Furthermore, in preliminary study, when we
try to matching jaw positions, periodontal or
temporo-mandibular joint mechanoreceptors
do not seem to be essential for sensing jaw
position. The proper jaw position seems to be
decided by muscular proprioceptive inputs.
Visual guidance could not improve the
precision of jaw position, but there is still
some confusion regarding the effect of visual
feedback on the velocity of mandibular
movement. The aim of the present study was
to observe how the visual feedback affects
the velocity of mandibular movement of
healthy subjects.
Material and Methods
Subjects
There were eighteen volunteer subjects (10
males, and 8 females), ages ranging from 21
to 24 years old, all of whom gave informed
consent prior to the experiment, jointed the
study. All subjects were in good physical
health and had no acute dental diseases.
They were free from any dysfunction of
Temporomandibular joints and related
stomatognathic structures after detailed
RDC-TMD examination. Protocol.
iomedical Engineering Association
The Influence of Visual Feedback on the Velocity of Mandibular Movement