Tip Back Bend in Continuous Archwire: 3D Analysis using Finite Element Method
Authors: Allahyar Geramy, Jean Marc Retrouvey, Hannane Ghadirian, Reza Jelodar and Hasan Salehi
Abstract: Aim: In spite of different straight wire techniques now available in market, wire bends are still important in daily clinical practice of orthodontics. The main goal of this study was to analyze the effects of different tip back configurations on their force system.
Material and Method: Six three-dimensional (3D) finite element models were designed. Each model contained a mandibular first molar and was designed with a buccal tube attached to its buccal surface, a segment of rectangular wire 0.4x0.55 mm2 of stainless steel in different designs. Loops were a simple tip back bend, an inverse helix, a vertical loop activated by diverging legs, a vertical loop with equal legs ( = 2.5 mm), a vertical loop with a short mesial leg, and a vertical loop with long mesial leg. Tooth occlusal surface was considered to be flat to ease calculations Each model was transferred to the ANSYS Workbench Version 10 Displacements were derived numerically in the level of the mesial and distal marginal ridges to show the differences in the reaction of the molar occlusal table nodes. Vertical displacements were assessed in four parallel planes medio-laterally in molar. In each plane 4 nodes were considered in equal distances mesio distally.
Results: Extrusion decrease order is: Apically Activated (1.17) > Simple tip back (1)> Mesial Short (1.05) > Inverse Helix(0.53) > Equal leg( 0.49) > Mesial long (0.49) Intrusion decrease order: Simple tip back = Inverse helix (=1) > Mesial Long (0.44) > Equal leg (0.31)> Apically Active (-0.4)> Mesial short (-0.98).
Conclusion: Apically activated loop is suggested for bite opening due to higher extrusion in mesio-buccal and lack of intrusion. The highest intrusion in distal side of the teeth is produced by simple tip back.The simple tip back is suggested for anchorage control.