RESUMEN
AIM: The aim of this study was to evaluate, by light microscopy, the effects of laser phototherapy (LPT) at 780 nm or a combination of 660 and 790 nm, on the inflammatory process of the rat temporomandibular joint (TMJ) induced by carrageen. BACKGROUND: Temporomandibular disorders (TMDs) are frequent in the population and generally present an inflammatory component. Previous studies have evidenced positive effects of laser phototherapy on TMDs. However, its mechanism of action on the inflammation of the TMJ is not known yet. MATERIALS AND METHODS: Eighty-five Wistar rats were divided into 9 groups: G1, Saline; G2, Saline + LPT IR; G3, Saline + LPT IR + R; G4, Carrageenan; G5, Carrageenan + LPT IR; G6, Carrageenan + LPT IR + R; G7, previous LPT + Carrageenan; G8, previous LPT + carrageenan + LPT IR; and G9, previous LPT + carrageenan + LPT IR + R, and then subdivided in subgroups of 3 and 7 days. After animal death, specimens were taken, routinely cut and stained with HE, Sirius Red, and Toluidine Blue. Descriptive analysis of components of the TMJ was done. The synovial cell layers were counted. RESULTS: Injection of saline did not produced inflammatory reaction and the irradiated groups did not present differences compared to nonirradiated ones. After carrageenan injection, intense inflammatory infiltration and synovial cell layers proliferation were observed. The infrared irradiated group presented less inflammation and less synovial cell layers number compared to other groups. Previous laser irradiation did not improve the results. CONCLUSION: It was concluded that the LPT presented positive effects on inflammatory infiltration reduction and accelerated the inflammation process, mainly with IR laser irradiation. The number of synovial cell layers was reduced on irradiated group.