The effects of Twin Blocks: a prospective controlled study.

This prospective controlled study investigated the net effects of the Twin Block functional appliance taking into account the effects of normal growth in an untreated control group. The treatment group consisted of 36 subjects, mean age of 12.4 years, consecutively treated with Twin Block appliances for an average period of 0.9 years. Each subject had immediate pre- and posttreatment lateral cephalograms. The control group consisted of 27 subjects with a mean age of 12.1 years. These patients were observed for a mean time of 1.2 years and had radiographic investigation at the initial consultation and immediately before the start of Twin Block therapy. The data were then annualized and subjected to multiple regression analysis. In the treatment group, a reduction in ANB of 2.0 degrees (p < 0.001) was observed largely because of an increase in SNB of 1.9 degrees (p < 0.001). No statistically significant restraint in the maxillary growth was observed. Treatment resulted in an increase in Ar-Pog of 5.1 mm (p < 0.001) compared with the control group increase in Ar-Pog of 2.7 mm, resulting in a net gain of 2.4 mm. The overjet was reduced by combination of a net maxillary incisor retroclination of 10.8 degrees (p < 0.001), net mandibular incisor proclination of 7.9 degrees (p < 0.001) and forward movement of the mandible. Buccal segment relationships were corrected by means of lower molar eruption, restraint in the eruption of the upper molars and forward growth or repositioning of the mandible. Any possible fossa adaption was not assessed.