Secondary retention of permanent molars: a histologic study.

The etiology of secondary retention is not well understood, but ankylosis is often considered to be an important factor in primary molars. Data concerning the mechanism of secondary retention in the permanent dentition are insufficient, although a possible role of ankylosis has been suggested. In order to analyze the frequency of occurrence and localization of ankylosis in secondarily retained permanent teeth, 26 secondarily retained molars and for comparison six normal molars were studied histologically. These data were compared with the clinical and radiographic findings. Areas of ankylosis were observed along the roots of all secondarily retained molars. In 81% of the cases these areas were located at the bifurcation and interradicular root surface. No signs of ankylosis were found in normal molars. When these results were compared with the clinical and radiographic data, it was obvious that the latter gave many false negative results, because the areas of ankylosis were often too small to be detected clinically or radiographically.