A PROSPECTIVE EVALUATION OF BASS, BIONATOR AND TWIN BLOCK APPLIANCES - PART I - THE HARD TISSUES

A prospective clinical study with a random allocation of 47 adolescent patients to three different functional appliance groups was establish ed and compared with an untreated control group over a 9-month period. Treatment was undertaken with either a Bionator, Twin Block, or Bass appliance. Pre- and post-treatment cephalograms were used to quantify the skeletal and dentoalveolar changes produced by the appliances and compared with those observed in the control group as a result of growt h. Both the Bionator and Twin Block appliances demonstrated a statisti cally significant increase in mandibular length (3.9 +/- 2.7 mm; 3.7 /- 2.1 mm, respectively) compared with the control group (P < 0.05), w ith an anterior movement of pogonion and point B. Highly statistically significant increases (P< 0.01) were seen in lower face heights for a ll the appliance groups compared with the control group. The Twin Bloc k group showed the least forward movement of point A due to a change i n the inclination of the maxillary plane. The Bionator and Twin Block groups showed statistically significant reductions in the inclination of the upper incisors to the maxillary plane (P< 0.05). The Bass group showed minimal change in the inclination of the lower labial segment to the mandibular plane. The Bionator group demonstrated the greatest proclination of the lower labial segment (4.0 +/- 3.6 degrees). Clinic ally important changes were measured in all the appliance groups when compared with the control group. Differences were also identified betw een the functional appliance groups. The Twin Block appliance and, to a lesser extent, the Bionator appeared the most effective in producing sagittal and vertical changes.