[Purpose] The aim of the present study was to assess the behavior of the mean and median
frequencies of the electromyography signal of the mastication muscles of adolescents with
different degrees of TMD severity. [Subjects] Forty-two adolescents aged 14 to 18 years.
[Methods] The adolescents were classified according to severity using the Helkimo Index.
The control group consisted of 14 subjects with no signs or symptoms of TMD. Three
readings were taken in during maximum intercuspation and mandibular rest, with each
reading lasting 10 seconds. [Results] Significant differences (p=0.0001) were found in the
mean frequency (Hz) between the control group (CG), mild TMD group (MG) and
moderate/severe TMD group (MSG), especially during mandibular rest, for all muscles
evaluated: right temporal: CG (137.5), MG (194.2), MSG (291.7); left temporal: CG (106.9),
MG (200.6), MSG (294.2); right masseter: CG (155.7), MG (242.8), MSG (278.3); left
masseter: CG (125.0), MG (214.6), MSG (316.7). Greater differences among groups were found
under the condition of mandibular rest. Conclusions: Adolescents with TMD especially those
with more severe symptoms exhibit hyperactivity of the mastication muscles.