A STUDY OF FORCE APPLICATION, AMOUNT OF RETARDING FORCE, AND BRACKET WIDTH IN SLIDING MECHANICS

We investigated the relationship of the retraction force to the locati on of force application, retarding force and bracket width during simu lated sliding tooth movement along an arch wire. Point 1 for retractio n was located at the center of the bracket, and points 2 and 3 were at 4.0 mm acid 6.0 mm from the bracket slot, respectively. Weights of 10 0 gm, 200 gm, and 400 gm were suspended at 9.0 mm from the bracket slo t as the point of simulated center of resistance. Stainless steel stan dard edgewise wide, medium, acid narrow twin brackets were engaged wit h two elastomeric ligatures on a stainless steel wire (0.016 x 0.016 i nch). The bracket was retracted at the rate of 0.1 mm per second for a distance of 2.0 mm. Measurements were repeated six times, and the res ults were compared with multiple ANOVA tests. For all brackets, with a n increase of the retarding weight, the mean retraction force at point s 1 and 2 increased but decreased at point 3. The mean retraction forc e at point 1 for the narrow twin bracket was significantly (p < 0.05) higher than that for the wide twin bracket at all retarding force leve ls. However, the mean retraction force at points 2 and 3 for the narro w twin bracket was significantly (p < 0.05) lower than for the wide tw in bracket at all retarding force revels. These findings indicated tha t the point of force application, the resistance force of a tooth, and the width of the bracket are crucial in consideration of the tipping moments on the bracket.