Ankylosis of primary molars--a future periodontal threat to the first permanent molars?

Most infra-occluded and ankylosed primary molars with a permanent successor will exfoliate normally. Continuous supervision of occlusal development and radiographic control of normal root resorption have been recommended. The decreased height of the alveolar bone level at the site of the infra-occluded primary molar has been reported to normalize after the eruption of the permanent successor. However, opinions that infra-occlusion of primary molars entails a risk of future periodontal damage to the first permanent molars have been presented. The aim of this study was to perform a long-term follow-up of the alveolar bone level mesial to the first permanent molars after spontaneous exfoliation or necessary extraction of the infra-occluded second primary molars. The material consisted of 143 permanent molars adjacent to 119 infra-occluded primary molars and 24 normal contralateral primary molars in 68 individuals. The subjects were re-examined about 8 years after the exfoliation or extraction of the infra-occluded second primary molars. The subjects were examined both clinically and radiographically. Alveolar bone level mesial to the first permanent molars was measured in bite-wing radiographs. All but two permanent first molars showed a normal alveolar bone level mesially. In two first permanent molars where the primary molar was extracted, mesial approximal bone loss amounted to 4 and 3 mm, respectively, but no pocket formation was found. Infra-occlusion and ankylosis of primary molars does not constitute a general risk of future alveolar bone loss mesial to the first permanent molars. The general treatment recommendation to await normal exfoliation and eruption of successors remains valid.