Timing of Class II treatment: skeletal changes comparing 1-phase and 2-phase treatment.

INTRODUCTION: Previous studies reported small but significant skeletal changes as a result of early treatment of Class II malocclusion with headgear and functional appliances. In this study, we report on the skeletal changes for 1-phase and 2-phase treatment of Class II malocclusion.

METHODS: This was a prospective randomized clinical trial conducted sy the Department of Orthodontics at the University of Florida between 1990 and 2000. A total of 261 subjects demonstrating at least a one half-cusp Class II molar relationship and meeting the inclusion criteria were enrolled in the study and had at least 1 follow-up visit. During phase 1, 86 subjects were treated with a bionator, 95 were treated with a headgear/biteplane, and 80 served as the observation group. For phase 2, all subjects were then treated with full orthodontics appliances. Skeletal changes were monitored with cephalograms taken at baseline, at the end of early Class II treatment or observation baseline, at the beginning of fixed appliances, and at end of orthodontic treatment.

RESULTS: Overall skeletal changes at the end of phase 1 treatment were as follows: (1) SNA angle increased in the bionator (0.51) and the observation groups (0.67), whereas it decreased (-0.50) in the headgear/biteplane group; (2) SNB angle increased in the bionator (1.36) and the observation groups (0.84), whereas it remained unchanged (0.19) in the headgear/biteplane group; (3) ANB angle decreased in the bionator (-0.85) and the headgear/biteplane groups (-0.72), and was unchanged in the observation group; and (4) the mandibular plane angle increased (1.30) only in the headgear/biteplane group. By the end of full orthodontic treatment, the skeletal differences in all measurements for all 3 groups were within 1 degrees . Linear regression models showed that, during phase 1, baseline value and treatment group were significant. However, when the entire treatment period was considered, treatment group had no effect.

CONCLUSIONS: There is temporary skeletal change as a result of phase I treatment with both appliances but no detectible skeletal difference between 1-phase and 2-phase treatment of Class II malocclusion by the end of full orthodontic treatment.