RESUMEN
Background: The relation of cause and effect between orthodontic treatment and joint dysfunction, especially disc displacement, is not proved yet. The orthodontic treatment that imposes stress on the temporomandibular joint is the mandibular advance to correct the classes II by mandibular retrognathia. The study aimed to explore the effect of mandibular advancement using rigid activator associated with extra-oral forces on the sagittal position of temporomandibular joint (TMJ) disc.Methods:63 children, 10.6 +/- 1 years old with class II and mandibular retrognathia were selected from primary schools. An imaging magnetic resonance exploration (MRI) was performed on 126 TMJ before treatment (t1) and one year after treatment (t2). The data were analyzed by the Statistical Package for the Social Sciences (SPSS).The error risk αwas 5%. The Friedman's Chi2 Test for paired data was used. The difference p was considered significant if p<0.05.Results: At t2, the discs generally occupied a more anterior position remaining within the bounds of normality and 5 of them have presented a displacement. Conclusion: Overall, after one year of mandibular advancement, the discs have maintained a normal position