Administration of Low-level Laser on Muscles of Mastication Following the Induction of Initial Fatigue

Orofacial pain encompasses painful conditions, such as temporomandibular disorder. Multidisciplinary health teams seek to control such musculoskeletal disorders to improve the quality and functional capacity of the muscles of mastication. The aim of the proposed study is to evaluate the effect of low-level laser therapy as a form of treatment for the prevention of initial fatigue of the muscles of mastication (masseter and anterior temporal muscles) as well as the recovery of these muscles after induced exhaustion (caused by isometric contraction) in young adults. The participants will be 78 (n obtained from calculation of the sample size with p < 0.05) healthy male and female volunteers between 18 and 34 years of age. The volunteers will be randomly allocated to a laser group (n = 26), sham group (n = 26) and control group (n = 26). All participants will be submitted to a clinical evaluation to record mandibular movements, bite force, muscle sensitivity to palpation and initial muscle fatigue. Initial fatigue will be induced by isometric contraction of the jaws. Maximum voluntary contraction will be performed to record the time until initial exhaustion of the masseter muscle (determined by electromyography). The groups will then be submitted to the interventions: 1) active laser therapy (wavelength: 780 nm; fluence: 134 J/cm2; power: 50 mW; irradiance: 1.675 W/cm2; exposure time: 80 seconds per point) on three points of the masseter and one point on the anterior temporal muscles on each side, 2) sham laser (placebo effect) or 3) no intervention (control). Maximum voluntary contraction will be performed again after the interventions to record the time until initial exhaustion of the masseter muscle (determined by electromyography). Differences in individual time until exhaustion between the pre-intervention and post-intervention evaluations will be measured to determine the effect of low-level laser therapy.