Posterior disk displacement of the TMJ: MRI evidence in two cases.

Posterior disk displacement is a rare temporomandibular joint (TMJ) disorder. The main clinical sign is sudden molar open-bite (jaw locked in the open position). This may be accompanied by a sensation of intra-articular foreign body and more rarely joint pain. Joint sounds are unremarkable. Mouth opening may be slightly impaired. Hypothetically, like anterior disk displacements, posterior disk displacements can be classified as either reducible or nonreducible. A definitive diagnosis requires magnetic resonance imaging (MRI). There is no consensus concerning treatment. A conservative course of treatment can be successful in patients with functional impairment and should always be attempted before irreversible, invasive therapy.