Proportional changes in cephalometric distances during Twin Block appliance therapy.

The aim of the study was to evaluate the cephalometric changes produced by the Twin Block appliance. Lateral cephalometric radiographs were taken before and after Twin Block appliance treatment on 30 consecutive patients (14 male, 16 female, mean age 12 years 6 months). Published normative data tables were used to produce control data, which were individually matched to the test group for age, sex, and treatment time. Alteration in shape was assessed by measuring percentage change in linear dimensions as opposed to change in cephalometric angles used in previous investigations. The differential average percentage change was calculated by subtracting the control value from the Twin Block value. Clinically significant changes (2 per cent and greater) were found in lower anterior (6.6 per cent) and posterior (4.6 per cent) face heights, upper incisor to maxillary plane (4.9 per cent), i.e. upper incisor retraction, and increase in mandibular length (Co-B 3.3 per cent, Co-Po 2.6 per cent, Ar-B 3.5 per cent, Ar-Po 2.2 per cent).