A Comparative Assessment Of Torque Capabilities Between Lingual And Labial Brackets Using Three-dimension Finite Element Method

Objective:To construct three-dimensional(3-D) finite element modelof Lingual and Labial Brackets with archwires based on finite element method,and to do the simulation of torque load on the left upper central incisors underdifferent materials and dimensions of archwires. Analyse the difference oftorque performance between Lingual and Labial Brackets as well as the patternof the influence that the archwires of different materials and sizes have on thetorque capability of Lingual Brackets, so as to provide theoretical reference forclinical treatments of torque controlling on the anterior teeth in lingualorthodontics.Methods:1. Construct solid model of lingual bracket withhorizontal slot and labial bracket with vertical slot from the right upper canine tothe left upper canine including0.20mm dimension ligation wires and edgewisearchwires and ribbon archwires of two dimensions（0.46×0.64mm2and0.48×0.64mm2）by using Pro/E Wildfire4.0software.In this study, all bracketswere of0.022-inch slot size.2.Assemble the solid model and lead to theMSC.Marc.Mentat2005R3software, and then setting up the3-D finite elementmodel of Lingual and Labial Brackets with archwires.3. Simulate the torqueload using MSC. Marc. Mentat software. Except the left upper central incisorsbrackets, the rest of the brackets and arch wires are fixed in three dimensional directions, take the center of the bracket slot of the left upper central incisors asthe central point and make these two brackets rotate clockwise andcounterclockwise with a rotation angle of20degree along the horizontal axis ofbracket slot. Simulate the torque load on the left upper central incisors withdifferent materials and dimensions of archwires.Calculate torque moment of thecorresponding center nodes of the brackets of the left upper central incisors andthe maximum moment of various operating conditions，and draw the curves oftorque moment/torque angle.Results:1. Construct3-D finite element model ofLingual and Labial Brackets with archwires by meshing reasonably andaccurately,which have the geometry morphology and biomechanical similarityof clinical brackets and archwires.2. The torque moment/angle curve of lingualbrackets was similar to labial brackets under the different dimensions andmaterials archwires. With the increase of torque degree, torque momentincreased gradually,and Stainless Steel(SS) increased greatest,followed byBeta-titanium(TMA) and Nickel-Titanium(NiTi).3. Under the same torqueAngle, lingual brackets produced greater force, the average of which is aboutthree to five times, than the labial brackets.4. The nature of the archwires hasthe similar influence on the lingual brackets torque performance as the labialbrackets. The growth in archwire dimension increases the lingual brackets torquemoment (SS was increased from0.46×0.64mm2to0.48×0.64mm2, torquemoment was increased to106%), but the change is less than that caused by wirealloy of the archwire (from0.46x0.64mm2NiTi to SS of the same size, torquemoment was increased to390%), even less than the change caused by both the dimension and material together (from0.46×0.64mm2NiTi to0.48×0.64mm2SS,moment was increased to414%). Conclusion:1. Apply the combination ofPro/E Wildfire and MSC. Marc. Mentat to develop3-D finite element model ofLingual and Labial Brackets with archwires, which can provide a reliable studyplatform for the mechanical properties of the brackets in biomechanical analysis.2.With the increase of torque degree,torque moments of lingual and labialbrackets increase gradually in each operating condition,especially in SS.3.Thelingual orthodontic brackets produced about3to5times of torque force of thelabial brackets under the same degree of torque angle.4. Torque performance oflingual bracket was affected by the characteristics of archwires.The effect ofarchwire dimension is less than the type of wire alloy.The synergistic effect ofthe size and material is the most.From0.46×0.64mm2Nickel-Titanium,0.46×0.64mm2Beta-Titanium,0.48×0.64mm2Nickel-Titanium,0.46×0.64mm2Stainless Steel to0.48×0.64mm2Stainless Steel, torque momentwas gradually increased.