Without bruxism and no intervention. They will be submitted to electromyographic assessment and evaluation of salivary cortisol and dopamine.

The volunteers in Group 2 will be submitted to the initial evaluation of the morphological and psychosocial variables. During the same appointment, red LED (3 X 6 cm) will be administered using a board with 6 LEDs with a wavelength of 650 nm ± 20 nm, seven-minute operation time, optical spot of 5 ± 2 mm and optical output of 2~5 mW, with a dose of 2.675 J/cm2. Further analyses will be performed immediately after the photobiomodulation session and one week later. They will be submitted before and after LED to electromyographic assessment and evaluation of salivary cortisol and dopamine.

They will be treated using the standard protocol of a rigid occlusal splint. After the initial evaluation, molds will be made for the fabrication of the splints, which will be delivered one week later. Written and verbal instructions for use will be given. After one month of daily use, the volunteers will return for the final morphological and psychosocial evaluations.

Subjects with bruxism. The same procedures as LED group, but the device will be turn off.

Infrared LED (3 X 6 cm) will be administered using a board with 6 LEDs with a wavelength of wavelength: 850 nm ± 20 nm, seven-minute operation time, optical spot of 5 ± 2 mm and optical output of 2~5 mW, with a dose of 2.675 J/cm2. Further analyses will be performed immediately after the photobiomodulation session and one week later.

Electromyography will be performed to complement the evaluation of the morphological aspects of the groups. The masseter and temporal muscles will be evaluated using a portable electromyograph (BTS TMJOINT) with wireless electrodes. The participant will be seated with Camper's plane parallel to the floor. Three readings will be made on both sides with the muscles at rest, during habitual maximum intercuspation (isometric contraction) and during simulated chewing with Parafilm (isotonic contraction). The signal will be captured for 10 seconds under each condition. The first chewing cycle will be discarded and the subsequent five cycles will be collected.

The participants and caregivers will receive verbal and written instructions to avoid any physical activity, the ingestion of substances with alcohol or caffeine, soft drinks, tea, corticoids and chewing gum in the 24h prior to the collection of the saliva. Saliva samples will be collected using swabs, which will refrigerated immediately after collection. The swab will be placed under the tongue. Samples with visible signs of blood will be discarded due to possible contamination. The swabs will be centrifuged at 3500 rpm for 5 minutes. The supernatant will be collected and stored at -40o C. Cortisol will be determined using an enzyme-linked immunosorbent assay. Dopamine will also be determined using an ELIZA kit. The samples will be thawed and centrifuged again. The procedure will follow the basic ELISA principle of competition between an untagged antigen and an enzyme-tagged antigen for a particular number of binding sites on the antibody.