The moment generated by the torque of the orthodontic rectangular wire : Three-dimensional finite element analysis

Ha, Do Won; Kim, Young Suk; Sung, Jae Hyun

Abstract

The purpose of this study was to investigate the ideal clinical torque(In the SWA rectangular wire, the torque by the angle between the plane part and twisted part to move the tooth) of the orthodontic rectangular wire which produce the proper labiolingual movement of the single tooth during finishing stage of the orthodontic treatment. The clinical torque is the sum of the play and the active torque which generates the moment at the bracket. The play is calculated by the formula and the active torque is calculated by the computer aided three-dimensional finite element method. The finite element model was consist of the three brackets which formed a row and 3 kinds of orthodontic rectangular wire(stainless steel, TMA, NiTi) which inserted in brackets. Both sides of the model were twisted and the moment generated in the center bracket was calculated. The sizes of seven wires which were used commonly were .016" X .022", .017" X .022", .017" X .025", .018" X .025", .019" X .025", .020" X .025", .021" X .025". In 018" bracket, 016" X .022", .017" X .022", .017" X .025" wires were inserted and in 022" bracket, all the sizes of wires except .016" X .022" were inserted and tested. The following conclusions could be drawn from this study. 1. The moments generated on the same size of the wires by the same active torque were equal regardless of the bracket slot size. 2. The moments were increased with the size of the wires. The moment generated on the .021" X .025" wire was about 1.75 times as large as that on the .016" X .022" wire regardless of the material. 3. The moments were increased in the order of the NiTi, TMA, stainless steel. The moment of the TMA wire was 0.35 times as small as that of the stainless steel wire and the moment of the NiTi was 0.16 times as small as that of the stainless steel wire. 4. The moment was decreased as the interbracket distance was increased. 5. To get a desired moment with the specific size and material of the wire on the specific bracket slot, the formula and the results were displayed.