Ectopic eruption of maxillary first permanent molars and association with other tooth and developmental disturbances.

The associations between tooth and eruption disturbances in four groups of children selected primarily with only one diagnosed eruption or developmental disturbance in each group was analysed. Ninety-two children were primarily diagnosed with ectopic eruption of maxillary first permanent molars, 93 children with infra-occlusion and ankylosis of primary molars, 91 children with ectopic eruption of maxillary canines, and 97 children with aplasia of premolars. Of the children studied 69-79 per cent had only a single one of the four disturbances studied. In 18-28 per cent there was one additional disturbance and in 2-3 per cent two additional disturbances. From chi square contingency tests, it was found that infra-occlusion of primary molars and aplasia of premolars exhibited a higher prevalence in both directions compared to the expected population prevalence. Ectopic eruption of maxillary canines showed a significantly higher prevalence than expected in all the other three groups. Our interpretation is that these results support the hypothesis of a common, presumably hereditary, aetiology. Thus, the four conditions studied would be different manifestations of one syndrome, each manifestation having an incomplete penetrance. With closer follow-up of the maxillary canines during the eruption period in children with some of the other three disturbances, prophylactic, or early interceptive measures may be taken and complicated orthodontic treatment be reduced or avoided.