Infraocclusion of primary molars: a histologic study.

In order to analyze the occurrence and character of ankylosis in primary molars in infraocclusion, 102 primary molars, 62 in infraocclusion and 40 in normal position, in children aged 3-17 yr, were studied histologically. Ankylosis was demonstrable in most of the infraoccluded teeth while ankylosis was not found in teeth with normal positions. The ankylosis was always located at the inner root surface. Progression of the resorption of the root with age was seen in both groups of teeth. In teeth of younger children, in contrast to teeth of older children, the ankylosis was never found in the cervical portion of the roots. In the mandible, a thicker buccal marginal bone crest could be found in infraoccluded teeth than in teeth in normal position. Bone biopsies revealed no pathologic changes. Pulps of infraoccluded teeth more often demonstrated degenerative changes like fibrosis and calcifications. It is suggested that ankylosis is a local phenomenon, most likely due to developmental disturbances of the periodontium, and that ankylosis in infraoccluded primary molars is not a static condition but part of an ongoing process during root resorption.