Research has indicated that the bite jumping technique employed by the crowned Herbst appliance can be effective in correcting Class II skeletal abnormalities by promoting growth of the mandible and remodeling of the glenoid fossa. This research investigated the skeletal and dental alterations of Class II patients treated at an early age with the edgewise crowned Herbst appliance and evaluated the long term stability of those effects. Methods: Cephalometric analysis was performed for a treatment group consisting of 22 radiographs taken before phase I treatment (T1), immediately after Herbst removal during phase I treatment (T2), at the completion of phase I treatment (T3), prior to beginning of phase II orthodontic treatment (T4), and immediately following phase II orthodontic treatment (T5). Measurements were compared to a matched control sample of untreated Class II patients from the Bolton-Brush study. The difference in each variable between the treatment and control groups across the five time periods was analyzed for pooled subjects, and separately for male and female subjects. The differences between certain time points were analyzed to investigate treatment changes and their stability over time. For all time periods, the change in the values of the variables for pooled subjects, male subjects, and female subjects in the treatment group were compared to the change in the values of the variables for pooled subjects, male subjects, and female subjects in the control group, respectively. In total, 37 variables were evaluated for each group including sagittal variables, vertical variables, angular variables, and condyle/glenoid fossa variables. In addition, an evaluation of the overjet correction and molar relationship correction for the treatment groups and an evaluation of the net overjet correction and net molar relationship correction for the treatment vs. control groups at each time period for pooled subjects were performed. Results: Treatment of Class II patients treated with the crowned Herbst appliance in the early mixed dentition resulted in the following changes relative to normal growth: The forward movement of the maxillary base (OLp-A pt) was initially restrained after treatment (T2-T1) and gradually became more restrained in the short-term (T3-T1) and long-term (T4-T1) post-treatment periods. An even greater restraint was seen after phase II orthodontics (T5-T1). The mandibular base (OLp-Pg) was initially moved forward after treatment (T2-T1), however, a gradual relapse was seen in the short-term (T3-T1) and long-term (T4-T1) post-treatment periods. Additional Dr. Peter Ngan, for his lifelong commitment to education, encouragement, expertise in the clinic, and general wisdom offered on a daily basis. I consider you not only a mentor, but a true friend. Dr. Chris Martin, for his everyday advice in the clinic, friendship, assistance with practice issues, support provided on the thesis, and full-time commitment to education.
