Chronology and histology of exfoliation and eruption of mandibular premolars in dogs.

Exfoliation of third deciduous mandibular premolars and their replacement by the third permanent premolars were compared in young dogs of purebred beagle and mongrel stock. Radiographic and histologic studies showed that eruption of the permanent premolar begins during the 16th postnatal week and is completed in 7 weeks. Root elongation proceeds with eruption, but fibers of the periodontal ligaments are not anchored in alveolar bone and do not attain their final orientation with respect to the long axis of the tooth until final phase of the eruptive period. These data define a predictable system in which various stages in the mechanism of eruption of noncontinuously erupting teeth may be examined experimentally. Furthermore, the observation that these processes are identical in timing and sequence in beagle and mongrel dogs suggests that less expensive, more readily available mongrel dogs can be used for these studies.