[MRI study of temporomandibular joint disk behavior in chilren with hyperpropulsion appliances].

Orthodontic and orthopaedic effects of hyperpropulsors have been studied, evaluating the possible adaptation of the temporo mandibular joint. Before the event of MR imaging, the positional modification of the disc could not be seen. The study has been carried out on 15 subjects, skeletal Class II, with a mean age of 11.6 years (SD = 1 year). A bilateral MR investigation has been done before and after the wear of an activator (Herbst or Monobloc with Head Gear). All patients underwent bilateral imaging in sagittal and modified coronal planes in closed and opened mouth. The qualitative analysis of the temporo-mandibular joints reveals the appearing of internal derangements, often asymptomatic, in one case out of five; the disc being anteriorly displaced on an average of 8.3 degrees (p = 0.023). These results need to be confirmed on larger samples but may modified functional approach of orthopaedic treatments in order to take into account the TMJ change.