Abstract
The longitudinal change of the tooth axes of the upper and lower permanent central incisors in subjects with reversed occlusion was examined by means of lateral cephalograms during the period from the deciduous dentition to the early mixed dentition. The effect of MPBA on the axes was also investigated. The untreated group consisted of 20 subjects with reversed occlusion at the deciduous dentition. Three cephalograms were taken for each subject at the following stages.
Stage A. At the deciduous dentition period. Average age was 4 years and 3months.
Stage B: At the deciduous dentition period. One year and 6 months after the first examination (Stage A).
Stage C: After the ruption of the lower permanent central incisors. The average was 6 years and 9 months. For comparison with the treated group,8 subjects of the stages A to B, and 4subjects of the stages B to C were added to the untreated group. All the cephalograms showed reversed occlusion. The treated group consists of 27 reversed occlusion subjects who were treated with MPBA. MPBA was applied to 13 subjects during stages A and B, and to 14 subjects during stages B and C.
The following results were obtained. In the untreated group, the angles of the tooth axes of the upper permanent central incisors decreased during the stages A and B, and increased during the stages B and C. As to the lower permanent central incisors, there was no specific trend during stages A and B, but the angles showed distinct increase during the stages B and C. When MPBA was applied. to the subjects with reversed occlusion at the deciduous dentition period, the unerupted upper central incisors showed significant labial inclination during stages A and B, and stages B and C, and the lower central incisors showed significant lingual inclination during stages A and B when the lower incisors had not erupted yet, and during stages B and C when they were erupting.
