Primary molar infraocclusion: frequency, magnitude, root resorption and premolar agenesis in a Spanish sample.

AIM: This study was conducted to determine frequency, distribution and magnitude of infraocclusion in primary mandibular molars; to evaluate root resorption, the frequency of premolars agenesis and the association between primary molar infraocclusion and premolar agenesis. MATERIALS AND METHODS: The sample consisted of 472 children who were subdivided in 3 age groups. The magnitude of infraocclusion was determined following the Bjerklin and Bennett method modified by the authors. Radicular resorption was determined using the rating scale proposed by Bjerklin and Bennett evaluating mesial and distal roots separately. The development degree of corresponding premolars was determined using the Demirjian method. RESULTS: One hundred and three (21.8%) children presented infraocclusion. The first primary molar presented infraocclusion in a significantly higher frequency. Considering the 3 scores of infraocclusion, 61.1% of the affected molars were classified as mild infraocclusion. No differences were found considering the root resorption pattern for primary molars, infraoccluded or not. Significant differences were found in the presence of agenesis in the group of infraoccluded molars. CONCLUSION: The present study identified a high percentage of infraocclusion, demonstrating that the type of molar is an influent variable, that the first primary molar is the most affected one, especially mandibular molars, and that the majority was mainly of a mild degree. There were no significant differences between the exfoliation of infraoccluded and non infraoccluded primary molars. However, radicular resorption of infraoccluded molars presented a clear delay or was totally absent in infraoccluded molars associated with premolar agenesis. Significant differences in the presence of agenesis beneath infraoccluded molars were observed.