An evaluation of two-phase treatment with the Herbst appliance and preadjusted edgewise therapy.

The purpose of this study was to evaluate the skeletal and dentoalveolar changes occurring during two-phase orthodontic treatment. A cephalometric study of Class II correction was carried out in 40 subjects (20 females, 20 males) who had been treated with the acrylic-splint Herbst appliance immediately followed by a second phase of preadjusted edgewise therapy. The average age at the start of Herbst therapy was 12.5 +/- 0.8 years for females and 13.6 +/- 1.2 years for males. Descriptive cephalometric data were compared with the normative values derived from the University of Michigan Elementary and Secondary School Growth Study. Control values were generated for each of the 40 Herbst patients based on gender, initial age, and duration of treatment. The results of this study indicate that the Class II correction achieved during Phase I treatment with Herbst appliance was due mainly to an increase in mandibular length, as well as distal movement of the maxillary molars and mesial movement of the mandibular molars and incisors. The accelerated mandibular growth rate observed during Herbst therapy was followed by a diminished growth rate during the edgewise phase that was less than control values. The overall increase in mandibular length was slight (approximately 1 mm), but significantly greater than control data for the whole group and the male subgroup; however, it was not significantly different between the treatment group and control data in the female subgroup. There were no significant treatment effects on lower anterior facial height and the mandibular plane angle at the end of either phase of treatment. The skeletal changes contributed to 55% of the molar correction during the Herbst therapy, whereas at the end of the second phase of treatment, skeletal change accounted for 80%. Significant anteroposterior dentoalveolar rebound was seen during the edgewise phase.