Abstract: Objective: To construct a three-dimensional finite element model of "2×4" appliance system simulating the clinical reality, and to investigate the effect of variation of bending location of tip-forward bending arch wires on the mechanical behavior in "2×4" appliance system.Methods: The 3-dimensional finite element model of "2×4" appliance system including maxillary dentition and brackets of tip-forward arch wires were constructed by reverse engineering method and the tip-forward bending arch wires with different bending locations[arch wire length from the point of arch wire to the central point of central incisor bracket/arch wire length from the central point of the buccal tube to the central point of central incisor bracket (A/L) were 0.8,0.7,0.6,0.5,0.4,and 0.3]were designed. The forces and moments of teeth under different tip-forward arch wires and the initial displacement of teeth under molar tip-forward arch wires were calculated by finite analysis software.Results: The force system changed as the bending locations of tip-forward arch wires varied. There were no vertical forces existed at A/L=0.41 for the first molar and incisors. There were no neutral points existed in the vertical force system(make the vertical forces=0 N in vertical direction). The moment of the first molar reversed when A/L=0.38 and the moment of lateral incisor reversed when A/L=0.59.The central incisor was affected under extrusion force without force and moment reverse as the bending location varied. The initial displacement of tooth was not conducive to the correction of anterior tooth apertognathia when A/L=0.8.Conclusion: The force system of three-dimensional finite element model of "2×4" appliance system changes as the varying of bending location of tip-forward arch wires. The molar tip-forward arch wire is unfavorable when correcting the anterior tooth apertognathia and the auxiliaries should be added.

Key words: anterior tooth apertognathia, tip-forward bending, finite element analysis, biomechanics