Infraocclusion of primary molars and the effect on occlusal development, a longitudinal study.

The long-term effect of infraocclusion of primary molars on occlusal development was studied to determine when orthodontic treatment should be carried out. Also, aetiological theories were evaluated. Altogether 56 children, 33 with bilateral infraocclusion and 23 with unilateral infraocclusion and normal contralateral sides, were followed up longitudinally until normal exfoliation took place or treatment was necessary. The study comprised 149 primary molars in infraocclusion. The registrations at the start included a clinical examination, lateral head films, orthopantomograms, intraoral periapical radiographs and dental casts. Every 6 months periodic identical intra-oral radiographs and study models were obtained. Most infraoccluded primary molars showed progression of the infraocclusion but all except five of the 149 teeth were spontaneously exfoliated, though with a delay of about 6 months. Negative effects on occlusal development were usually temporary and normal conditions were present after eruption of the permanent successors. Five infraoccluded primary molars had to be extracted. The general treatment recommendation is to await normal exfoliation of infraoc-cluded primary molars. Continuous supervision of occlusal development and periodic radiographic control of normal root resorption are recommended. Only in special cases (occlusal disturbances with severe tipping of neighbouring teeth and space loss, malposition of the permanent successor preventing normal root resorption and severe infraocclusion etc.) is extraction necessary. Taken together, the findings suggest a local cause of infraocclusion of primary molars, possibly of genetic origin in the dental and surrounding structures.