Stability of Class II treatment with an edgewise crowned Herbst appliance in the early mixed dentition: Skeletal and dental changes

Abstract

The objectives of this research were to assess skeletal and dental changes in patients with Class II malocclusion treated with the edgewise crowned Herbst appliance in the early mixed dentition and to measure the stability of treatment after a second phase of fixed appliance therapy. Twenty-two patients (ages, 8.4 ± 1.0 years) with Class II Division 1 malocclusion treated consecutively with the edgewise crowned Herbst appliance in the early mixed dentition were studied. Lateral cephalograms were taken before Herbst treatment, immediately after Herbst treatment, and after a second phase of fixed appliance therapy. The results were compared with a control group of untreated Class II subjects selected from the Bolton-Brush study, matched by age, sex, and craniofacial morphology. A total of 37 sagittal, vertical, and angular cephalometric variables were evaluated. Changes in overjet and molar relationship were calculated. Changes due to growth were subtracted to obtain the net changes due to treatment. The data were analyzed by using analysis of variance (ANOVA) and the t tests. Overcorrection with the Herbst appliance resulted in an average reduction in overjet of 7.0 mm and a change in molar relationship of 6.6 mm. Several factors contributed to the change in overjet: restraint of the forward movement of the maxilla (0.4 mm), forward movement of the mandible (2.0 mm), backward movement of the maxillary incisors (3.7 mm), and forward movement of the mandibular incisors (0.9 mm). Skeletal changes together with a 3.1-mm backward movement of the maxillary molars and a 1.1-mm forward movement of the mandibular molars contributed to the changes in molar relationship. After the second phase of fixed appliance therapy, the change in overjet was reduced to 2.8 mm. Most of the remaining overjet corrections were contributed by the restraint of maxillary growth (2.8 mm). The mandible moved posteriorly by 1.6 mm, and the mandibular incisors moved forward by 0.2 mm. Change in molar relationship was reduced to 2.2 mm. The maxillary molars moved backward by 0.2 mm, and the mandibular molars moved forward by 0.8 mm. Overcorrection of Class II malocclusion with the edgewise crowned Herbst appliance in the early mixed dentition resulted in a significant reduction in overjet and correction of the molar relationship. A portion of the correction was maintained after a second phase of fixed appliance therapy because of the continuous restraint of maxillary growth and the dentoalveolar adaptations.