Evaluation of Effects of Various Alpha and Beta Angulations for T-loop Made of Stainless Steel and Titanium Molybdenum Archwires during Space Closure: Finite Element Method (FEM) Study.

Space closure follows the initial stage of levelling and alignment in Pre-adjusted Edgewise treatment. There are majorly two methods of space closure, Loop mechanics and Sliding mechanics. Loop mechanics or frictionless mechanics is a preferred method because of its potential to produce pre-determined moment-to-force ratios which accurately achieve controlled movement of teeth. The aim of this finite element study was to evaluate the effects of three types of retraction loops with different moment bends (alpha and beta) made of 0.016"×0.022" stainless steel and TMA archwires with Finite Element Analysis. A Finite element model of CAD geometric model of standard MBT prescription (0.018" slot), Stainless Steel and Titanium Molybdenum Alloy (TMA) wire (0.016" × 0.022") and 3 loops (T-loop, Open Vertical and Closed helical loop) were constructed. A solid model of upper jaw with all permanent maxillary teeth except 1st premolar (extraction) with surrounding periodontal ligament and alveolar bone was prepared. Force, moment to force ratio, mesio-distal crown tipping, mesio-distal root tipping and vertical root movement (extrusion) were measured for different alpha and beta bends in anterior and posterior segments respectively. Force values without moment bends was found to be highest in open vertical loop in both anterior (SS- 414gms; TMA- 255gms) and posterior region (SS-540; TMA-370gms) with both SS and TMA wires. Moment to Force ratio (M/F) at both anterior and posterior segment was found to be highest in T-loop followed by closed helical loop and least in open vertical loop. Extrusion was found to be minimal in T-loop followed by closed helical loop, was maximum in open vertical loop. T-loop showed maximal control in terms of minimal extrusion and maximum M/F ratio amongst the three loops.