A Comparative Assessment Of Torque Capabilities Expression Between Lingual Brackets With Vertical And Horizontal Slot Using Three-dimension Finite Element Method

Objective:There are two kinds of direction slots lingual brackets on clinical conventionally,one is the vertical slot lingual brackets;the other is horizontal slot lingual brackets.In this experiment,two kinds of direction slots lingual bracket system were chosen: Incognito personalized lingual bracket with vertical slot and the seventh generation Kurz lingual bracket with horizontal slot.To establish anterior teeth three-dimensional finite element model of the vertical slot lingual bracket matching ribbon bow and horizontal slot lingual bracket matching the level of the bow based on three-dimensional finite element method,to use two sizes and three material archwire in clinical commonly simulated clinical left maxillary central incisor torque load and to analysis lingual brackets torque control performance difference between the two direction slots under the influence of archwire factors,to provide theoretical reference for clinical treatment.Methods:1.According to computer-aided measuring vertical slot lingual brackets and horizontal slot lingual brackets data,construct the solid model of these lingual brackets from the left maxillary canine to the right canine by solid modeling software Pro/E.Wildfire5.0,each model has 38 entities,including two slots lingual brackets with 0.018inch(0.46mm)slot size,matched archwires and 0.2mm ligation wires.Archwire selected three commonly clinical material,StainlessSteel(SS),Beta-titanium(TMA),Nickel-Titanium(Ni Ti)and posttreat-ment clinical commonly used in two sizes,0.016×0.022inch(0.41mm×0.56mm)size and 0.017×0.022inch(0.43mm×0.56mm)size.2.Solid models were imported into MSC.Patran software,selecting the tetrahedral cell of these two lingual brackets,archwires,ligation wires,total 29,023 nodes,95,537 elements.3.The completed models meshing were divided among three groups: brackets group,archwires group and ligation wires group,then imported into MSC.Marc.Mentat2005R3 software,simulating the clinical left maxillary central incisor torque load.In each set of model right maxillary arch wire ends sectional selected four points and bottom of all the brackets except the left maxillary of four fixed points,limited rotation and displacement of the three-dimensional direction,to select the left maxillary central incisor bottom center as the loading point and simulate clinical different size and material conditions,the two lingual brackets torque load 20 °.That is to say,make these two brackets rotate counterclockwise with a rotation angle of 20 degrees along the horizontal axis of bracket slot.Recording different models left maxillary central incisor torque loading point change as the toque angle,calculating each draw condition model,torque moment/torque angle graph and a bar graph the maximum torque moment.Results:1.Establish Anterior teeth segment three-dimensional finite element model successfully in line with the clinical characteristics of vertical slot personalized lingual brackets and horizontal slot lingual brackets and archwires ligation wires,reasonable precise grid division,so that the model has almost the same with the clinical geometry andmechanical properties.2.When the archwire size and material do not change,these two lingual brackets produced different torque moment,the lingual orthodontic brackets of vertical slot produced about 1 to 2 times of torque force of the horizontal lingual brackets under the same degree of torque angle;The influence of archwire changes to these two lingual brackets produced the same regular,when only the archwire size changed,these two lingual brackets torque moment are increasing with torque angle,the finer archwire size,the finer the torque moment.For example,in vertical slot lingual brackets,0.43mm×0.56 mm size archwire torque moment is about 1-2.5 times of 0.41mm×0.56 mm size archwire;When the arch wire dimensions remain unchanged,the arch wire material changed,these two lingual brackets torque moment related to archwire material elastic modulus,elastic modulus greater,the torque moment greater,NiTi changed to TMA,or TMA became SS,NiTi into SS,the elastic modulus difference,the torque moment fold change greater,ranging from 2.5-7 times in vertical slot lingual brackets;When the archwire material and size both changed,the torque moment of these two lingual brackets changed the maximum up to3-8 times.3.Two different direction slots lingual brackets contrasted,the archwire factors affecting of any one of the lingual brackets is the duplicate,the archwire size changes,at the same torque angle,torque moment of vertical slot lingual bracket value is 2-3 times of the horizontal lingual brackets;Archwire material changed in the same torque angle,the torque moment value of vertical slot lingual bracket is 3-9 times of the horizontal lingual brackets;When both two archwire factors changed,the torque moment value changed 5-10 times.Conclusion:1.Three-dimensional finite element model were established by Pro/E Wildfire5.0 and MSC.Marc with strong similarity in geometric and mechanical to clinical practice,credible clinical simulation,could meet similar clinical simulated load.It can effectively to comparative assessment of torque capabilities between lingual brackets with vertical and horizontal slot.2.Both of lingual brackets torque moment increased with torque angle,the slope of the increase was slightly different,proportional to the size and elasticity modulus of the archwire.3.Direction slot of lingual brackets had an impact to torque control performance,with torque angle increasing,vertical slot lingual brackets torque moment about 1-2 times of the horizontal brackets,but its impact is less than the archwire factors.4.Archwire factors influenced these two lingual brackets in the same.The effect of archwire size is less than the type of wire material.The synergistic effect of the size and material is the most.5.The toque control performance of the vertical slot lingual brackets is better than the horizontal one.Small torque angle can achieve high torque performance.However,archwire is a bigger influence factor for torque moment.The torque moment is too larger to fine control anterior teeth in SS archwire.The NiTi archwire is soft,but formability is poor,just suitable for early orthodontic stages but the TMA generates a suitable torque force.It can be used for clinical fine control.