Download Lateral pterygoid and other masticatory muscles activity in te

LATERAL PTERYGOID AND OTHER MASTICATORY MUSCLES
ACTIVITY IN TEMPOROMANDIBULAR JOINT INTERNAL
DERANGEMENT AND CONTROL SUBJECTS DURING DYNAMIC
CONDITIONS
C.M. Lafrenière1 PT, M. Lamontagne1,2 PhD & R. Elsawy M.D.
School of Human Kinetics1 and Dept. of Anatomy and Neurobiology2,
University of Ottawa, Ottawa, Ontario Canada
INTRODUCTION
TMJ practice is in a state of confusion because there is no consensus as to the nature and the cause
of ID. The leading voices proposed a muscular/active cause on top of the list whether primary or secondary
to posture, malocclusion, trauma, stress and parafunction in opposition to a possible passive or nonmuscular origin. The most popular hypothesis is that muscle hyperactivity of the masseter and temporalis is
a cause or a consequence of TMJ disorders (Dahlstrom, 1990; Jankelson, 1990; Sheikholeslam et al.,1982).
On the other hand, the Lateral Pterygoid Muscles (LPMs) were described as being hyperactive, hypoactive
and exhibiting altered activity definitely suggesting a close relationship between the functions of the LPMs
and TMJ ID (Mahan et al., 1983; Isberg et al., 1985; Zijun et al., 1989; Juniper, 1984). Probably because
they are anatomically and functionally related to the intra-articular joint mechanics. Various limitations of
previous studies are as follow: inexplicit samples, uncontrolled head and neck posture which may lead to
hyperactivity, conclusions based on theoretical reports, simply just done on normal subjects, on the masseter
and temporalis or during static tasks analysis only.
Therefore there is a necessity to bridge the gap in further understanding the TMJ muscle mechanics
in regards to ID. Hence, masticatory muscular activity measurements need to be examined during dynamic
jaw motion between TMJ ID and control subjects.
Consequently, the purpose of this study was to record and analyze the myoelectric activity of four
masticatory muscles with a special attention to the two heads of the LPMs during functional dynamic jaw
motion in subjects with and without TMJ ID disorders. The LPMs were investigated because they are
believed to be abnormally recruited in TMJ ID. The masseter and the temporalis muscles were recorded to
correlate their activity with the LPMs and to assess their recruitment pattern and contribution in TMJ ID in
order to have a complete masticatory picture.
METHODS
Intramuscular EMG of the two LPMs, surface EMG of the temporalis and masseter muscles, two
custom-made force transducers, electrogoniometry and joint sound recordings were used in synchronisation
to investigate the muscular mechanics associated with TMJ ID compare to controls during dynamic openclose-clench (OCC) cycles and functional gum chewing motion. Four measures were computed: 1-the
integrated linear envelope EMG (ILEEMG)
normalized by 100% Maximum Voluntary
Contraction (MVC) per OCC phase; 2- the
normalized ILEEMG by MVC by primary function;
3- the normalized ILEEMG by peak; and 4- a
descriptive analysis of the EMG signals. All of these
were computed for the 4 muscles and the 2 groups.
RESULTS AND DISCUSSION
Results showed that, overall, there was no
strong reason to believe that the masseter (figure 1)
and the temporalis are associated with TMJ ID in a
hyperactive manner as previously reported
(Dahlstrom, 1990; Jankelson, 1990; Sheikholeslam
et al.,1982). In general, the TMJ ID subjects
muscles functioned closer to their MVC or were
firing more compare to controls per chewing phase,
per primary function and by peak (figure 2). This
Figure 1. Normalized ILEEMG of the masseter
muscle by 100% MVC per phase of the OCC cycle
for both groups. The open phase was normalized by
the MVC in opening, the close and clench phase
were normalized by the MVC in molar clench.
could probably be secondary to a lack of strength, lack of stability, lower muscular endurance, inefficiency
and fatigue widely found in TMJ ID subjects, hence they are using greater relative forces during chewing
activities (Mahan et al., 1983; Carlsson, 1974).
Normal function of the ILP and SLP were
refined: the ILP seemed to be active only in forced
opening and as a synergist or a co-contractor in
clenching probably to gain stability in order to
provide protective splinting and coordinate fine
movements (Gibbs et al., 1983). Even if the results
were variable per muscle and per subjects,
dysfunctions of the ILP and SLP could definitely be
detected in ID: for the SLP results varied per phases
but showed hypercontraction in dynamic phases
and hypocontraction during clenching. In TMJ ID
cases, the two muscles seems to become dependant
and somewhat synchronous as well as exhibiting
uncoordinated and altered muscular activities likely
Figure 2. Normalized ILEEMG by peak of a gum
to compensate for the lost of inner-joint stability.
chewing cycle for the four muscles for both groups.
The results also demonstrated the
complexity of the LPMs function during dynamic
motions as controllers of the joint and discal units. It is suggested that TMJ clicking might be a consequence
of muscular incoordination, as reported previously and that a neuromuscular adaptation is happening in ID
of the TMJ to permit stability for effective chewing and survival. This plasticity of the masticatory muscular
mechanics has been well named “internal rearrangement” by Ogus (1987). Finally, causes, pathogenesis,
consequences and treatment principles of TMJ ID are discussed.
REFERENCES
Dahlstrom, L. (1990) J Oral Rehab 16,1-6.
Carlsson GE: Front Oral Physiol 1974;1:265-292.
Gibbs Hertling D, Kessler M: (1983) New York:
Isberg, A., Wildmalm, S.V. and Ivarsson, R. (1985) Am J Orthod 88(6), 453-460.
Jankelson, R.R. (1990) Pathophysio.Head & Neck Musculosketal disorders 7, 83-98.
Juniper, R.P. (1984) Br J Oral Maxillofac Surg 22,1-8.
Mahan, P. E., Wilkinson, T.M., Gibbs, C.H., Mauderli, A., Brannon, L.S. (1983) J Prosthet Dent
50(5),710-718.
Ogus H: (1987) Brit Ass Oral MaxilloSurg 218-226.
Sheikholeslam, A., Moller, E. & Lous, I. (1982). Scand J Dent Res 90,37-46.
Zijun, L., Huiyun, W. and Weiya, P. (1989) J Prosthet Dent 62(2),229-233.