Objective To study the influence of two slot size brackets on torque control when teeth interacted in the same arch. Methods After the upper arch was aligned and leveled in Typodont study, the inclinations of upper teeth 5┼5 were measured when 0.457 2 mm×0.635 0 mm OPA-K brackets and 0.558 8 mm×0.711 2 mm OPA-K brackets were filled with 0.431 8 mm×0.635 0 mm stainless steel wire. This experiment was duplicated 10 times. The inclin of each tooth were transformed to the absolute values of the torque play angle ψ by computing program, and paired-t test was used. Results The two kinds of slot size brackets were different with statistical significance on torque control. When the brackets were filled with 0.431 8 mm×0.635 0 mm stainless steel wire, the absolute values of the angle ψ in 0.558 8 mm×0.711 2 mm and 0.457 2 mm×0.635 0 mm slot size brackets were 6.140°±3.758° and 2.608°± 1.479° respectively, and the average difference of that between the two slot size brackets was 3.532°. The absolute values of the angle ψ in the upper left and right canine brackets were 2.560°±2.605°, 4.230°±2.817°, 1.260°±0.747° and 2.070°±0.663° respectively, and average differences between them were smaller than that in the other teeth. Conclusion There was difference between the two kinds of slot size brackets on torque control, and 0.457 2 mm×0.635 0 mm slot size bracket controls torque better when filled with the same size wire. In this study, the teeth interaction in the same arch probably caused the result that the difference of two slot size brackets on torque control was less than the study results of the theory calculations and material studys before.
