Second Molar Uprighting with Temporary Anchorage Devices: A Finite Element Study

BACKGROUND AND OBJECTIVE: Premature loss of mandibular first molar is a common problem in adults. Mesial tipping of second molar may occur in this situation. Various orthodontic mechanics have been proposed for molar uprighting. The aim of this study was to compare four methods of molar uprighting using Finite Element Analysis(FEM). METHODS: In first model of this finite element study, a 0.019×0.025 inch beta-titanium segmental arch wire with a T-loop was used. In second model a miniscrew was inserted in retromolar space and force was applied using elastomeric chain. The third model was a piece of 0.016×0.022inch beta-titanium wire with a bend which was placed more occlusal than the screw. The fourth model contained a mesially inserted miniscrew with an angle of 70 degrees to bone surface and a 0.018×0.025inch beta-titanium wire with helix. Extrusion, center of rotation and stress distribution in PDL during movement was compared between methods. FINDINGS: Buccal cusp extruded 1.36E-03, 1.13E-03, -9.74E-04 and 1.49E-03 mm in first, second, third and fourth model, respectively. Similarly, in lingual cusp, the amount of vertical displacement was at least in third model (-6.83E-04 mm). This amount in second and first method was 1.12E-03 and 4.05E-04 mm, respectively. The maximum amount of extrusion of lingual cusp occurred in fourth model (9.01E-03 mm). Mesial and distal cusps extruded 2.12E-04 and 1.58E-03 mm in first model, -1.14E-03 and 3.80E-03 mm in second method, -2.37E-03 and 7.04E-04 mm in third design and, 1.88E-03 and 8.57E-03 mm in the fourth model. The center of rotation was located at molar bifurcation in third model. CONCLUSION: The maximum amount of extrusion in both mesiodistal and buccolingual path was seen in fourth model. The best type of movement was found in third model, in which minimum extrusion occurred and center of rotation located at molar bifurcation.