Long-term follow-up of patients treated with the edgewise crowned Herbst appliance in the mixed dentition

Abstract

Objectives. 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 relapse in a posterior direction was seen after phase II orthodontics (T5-T1). The maxillary molars (Ms-OLp) were initially distalized (T2-T1), relapsed slightly in the short-term post-retention period (T3-T1), and became distalized again in the long-term post-treatment period (T4-T1). The maxillary molars were mesialized during phase II orthodontic treatment (T5-T4) and most of the overall posterior molar movement was eliminated after this period (T5-T1). The mandibular molars (Mi-OLp) were initially mesialized after treatment (T2-T1), however gradual relapse occurred during the short-term post-treatment period (T3-T1) until they returned to their pre-treatment position after the long-term post-treatment period (T4-T1). They were mesialized again after phase II orthodontic treatment (T5-T1). The maxillary incisors (Is-OLp) moved backward and retroclined after treatment (T2-T1), then relapsed slightly during the short-term (T3-T1) and long-term (T4-T1) post-treatment period. A net posterior movement was maintained through the long-term post-treatment period (T4-T1). This posterior position of the maxillary incisor remained stable through phase II treatment (T5-T1). The mandibular incisors (Ii-OLp) moved forward and proclined after treatment (T2-T1), then relapsed to their pre-treatment position after the short-term post-treatment period (T3-T1). Forward movement and proclination occurred during the long-term retention period (T4-T3), giving a net forward movement and proclination after this period (T4-T1). The mandibular incisors returned to their pre-treatment position after phase II orthodontic treatment (T5-T1). A net overjet correction of 7.0 mm occurred after treatment (T2-T1), then relapsed in the short-term post-treatment period (T3-T1) until a relatively stable net overjet correction between 2.5-3.0mm was maintained over the long-term (T4-T1). The overjet correction remained stable through phase II treatment (T5-T1). A molar relationship correction of 6.6 mm occurred after treatment (T2-T1), then relapsed in the short-term post-treatment period (T3-T1) until a relatively stable net molar correction between 2.2-3.3mm was maintained over the long-term (T4-T1). The molar correction remained stable through phase II treatment (T5-T1). Relocation of the glenoid fossa occurred in an anterior and superior direction after treatment (T2-T1) and this relative change in position was stable over the long term (T4-T1). Restriction of the downward and backward movement of the fossa was observed and might additionally contribute to Class II correction. Conclusions. The results of this study suggest that early treatment with the edgewise crowned Herbst appliance can achieve overjet correction and molar relationship correction that remains stable over the long-term. However, the skeletal and dental contributions to this overjet and molar correction shift over time with decreasing skeletal contribution and increasing dental compensation. During phase II orthodontic treatment, an increased skeletal contribution to overjet and molar relationship correction occurs