MANDIBULAR GROWTH DURING INITIAL TREATMENT WITH THE BASS ORTHOPEDIC APPLIANCE IN RELATION TO AGE AND GROWTH PERIODS

The aim of this study was to relate the initial orthopaedic effects of a Bass activator to age and growth periods at the time of therapy. Th e sample consisted of 54 boys with a severe Class II, division 1 maloc clusion. The mean age at start of treatment was 11.4 years. Longitudin al records of standing height were used to assess the growth period du ring treatment. Three periods were established: pre-peak, peak and pos t-peak. The treatment period of each subject was assigned to one of th ese periods. Lateral cephalograms were available 6 months before treat ment in 22 of the boys, and at the start of treatment and after 6 mont hs in the whole sample. No significant growth changes were observed 6 months before treatment. During the initial 6 months of treatment a sm all restraining effect on the maxilla and a forward growth of the mand ible was observed. A significant correlation between age and forward g rowth of the mandible during treatment was found in the pre-peak and p eak groups. This indicates a great initial orthopaedic treatment effec t in young boys in the pre-peak period and in boys with an early peak. In boys 10 years of age or older not having reached the peak period o f growth, the treatment response was less pronounced.