Spontaneous reeruption of a secondarily retained permanent lower molar and an unusual migration of a lower third molar.

Secondary retention refers to cessation of eruption of a tooth after its emergence. It occurs mainly in the deciduous dentition, but it is also seen on rare occasions in the permanent dentition. Although ankylosis has been suggested as the main etiologic factor, the exact biologic mechanism of secondary retention is not yet known. This article presents a case of spontaneous reeruption of a secondarily retained permanent molar, which is very rare. It also describes an unusual migration of a lower third molar in the same patient.