[Changes and stability of the cant of occlusal plane following orthodontic treatment]

The purpose of this study was to investigate the changes of the cant of occlusal plane during and after orthodontic treatment. Materials consisted of lateral roentgenocephalograms of 42 patients treated with full brackets system. Cephalograms were taken at following 4 stages; the beginning of orthodontic treatment, the beginning of retention, the end of mechanical retention and 3 years after the end of retention. Measurements were done at following angles and distance. 1. SN--occlusal plane angle 2. palatal plane--occlusal plane angle 3. mandibular plane--occlusal plane angle 4. Xi point--occlusal plane distance The results were as follows: 1. The SN-occlusal plane angle tended to decrease as time passed, although the pattern of the changes was different among Cl. I, Cl. II and Cl. III groups. 2. The changes of the occlusal plane mainly occurred within the limit of alveolar process. 3. Extension line of the occlusal plane tended to be close to the Xi point as time passed. 4. When the SN--occlusal plane angle was changed largely during the orthodontic treatment, it tended to relapse more after treatment.