Tooth Versus Mini-Screw Loading in Orthodontic Force Application: An Energy Analysis Using Finite Element Method
Authors: Allahyar Geramy
Abstract: Aim. Absolute anchorage during orthodontic treatment neutralizes unfavorable tooth movements caused by reaction forces. Mini screws were designed and introduced to serve as the source of an acceptable stationary anchorage. The main aim of this study was to assess the strain energy of involved tissues in mini screw and tooth loading in orthodontic force application to provide a better understanding of the energy state of the involved tissues. Materials and Methods. A 3D finite element model containing first and second molars, their periodontal ligament (PDL), spongy and cortical bone was modeled in SolidWorks 2006 and transferred to ANSYS Workbench (Ver.11). At first stage, a 2.5 N decomposed in 3D space was applied to the mini screw (E1) and at the second stage; the same force system was applied to the first molar (E2). Strain energy of the involved tissues was assessed and compared. The ratio of energy input (E1/E2) in two stages of analysis in each tissue was discussed. Results. The lowest ratio (E1/E2) finding was in the first molar (= 0.0003) followed by the PDL of the first molar (= 0.0027)which can be interpreted and equivalent to an anchorage reinforcement. This ratio is increased in the second molar (= 0.143) and its PDL (= 0.228).Ratios greater than one are noticed in the spongy bone (= 2.348) and cortical bone (= 8.17). Conclusion. Shifting from conventional tooth loading to mini screw loading during orthodontic treatment decreases the energy input to both teeth and the PDL which shows its positive anchorage effect and increases the energy input in the spongy and the cortical bone which seem to tolerate it due to their mineralized structure. A degree of periodontal ligament involvement in case of mini screw loading was also shown.