The Effects Of Mini Implant And Anterior Arch Hook Heights On En Masse Retraction: A Finite Element Analysis

IntroductionTo assess the maxillary anterior teeth and molars displacement trend at differentanterior arch hook (AAH) and mini implant (MI) heights.Materials and MethodsMaxilla finite element models were constructed from a cone beam CT scan of apatients’ oral facial region. The initial displacement of teeth were assessed afterapplying200g force between the hook and the mini-implant using Nickel titaniumclosed coil for extraction space closure clinical simulation model. The arch wires wereassumed to be0.019×0.025stainless steel engaged in0.022slot conventionalbrackets. The teeth displacements in vertical and sagittal planes were examined atvarious MI and AAH heights.ResultsThe lower MI position caused extrusion of the central incisors, but the teeth wereintruded at higher (6mm and8mm) MI heights.While the shorter (2mm and4mm) hooks intruded the central incisors, the higher(6mm and8mm) extruded the teeth. The higher MI and hooks reduced the palataltipping of central incisors.The distobucal cusp of the first molar was intruded, while the mesiobucal cusp wasextruded in all models: nonetheless, the shorter hooks and low MI had small molartipping effects.Conclusions1. The higher MIs caused intrusion and less palatal tipping of the central incisorscrowns with molar’s distobucal cusp intrusion.2. The increase in hook height resulted into extrusion and reduction in palataltipping of the central incisors crowns.3. The shorter hooks and low MI reduced the first molar tipping by limiting the intrusion of the distobucal cusp.