Mandibular growth rotation effects on postretention stability of mandibular incisor alignment

OBJECTIVE: To test the hypotheses that pronounced forward and backward mandibular growth rotation may be risk factors for postretention relapse of mandibular incisor alignment, and that morphologic parameters at adolescence may be predictive of the remaining type of mandibular growth. MATERIALS AND METHODS: Cephalograms and study models were made before (T1) and after (T2) active treatment and at a minimum of 10 years postretention (T3) of three groups of orthodontic patients with acceptable occlusion at the time of appliance removal. The groups were short facial height (n = 46), angle between the sella-nasion line and the mandibular plane (SN/MP) or= 38 degrees at T2. RESULTS: The groups were similar regarding age at T2, gender ratio, incisor irregularity (IRI), intercanine (3-3) width at T1, change of 3-3 width from T1 to T2, and time from T2 to T3 (P > .05). IRI increased in all groups from T2 to T3 (P < .05), but there were not any intergroup differences in this increase (P > .05). Minor differences were detected among the groups in mandibular growth rotation from T2 to T3. Males experienced more forward rotation than females (P < .001) and more increase in IRI from T2 to T3 (P < .01). Male gender, T1-T2 increase in 3-3 width, and T2-T3 reduction in 3-3 width were included in the model explaining T2-T3 increase in IRI. CONCLUSION: High-angled and low-angled facial patterns at time of appliance removal are not associated with increased risk of postretention relapse of mandibular incisor malalignment, and in adolescent orthodontic patients are poor predictors of type of posttreatment growth.