title: Dynamic simulation of the self-tapping insertion process of orthodontic microimplants into cortical bone with a 3-dimensional finite element method.
abstract: BACKGROUND
  The aim of this study was to evaluate the stress state in the cortical bone around an orthodontic microimplant during and after the insertion surgery.
  
  
  METHODS
  The self-tapping insertion of an orthodontic microimplant into 1-mm-thick cortical bone containing a predrilled hole was simulated by using a 3-dimensional finite element method. The entire insertion surgery was replicated by a total of 3601 calculation steps: ie, the first 3600 dynamic steps analyzing the insertion process and an additional static step for analyzing the residual stress state after insertion. Four microimplants were experimentally inserted into rabbit tibiae to measure the insertion torques and compare them with the finite element analysis results.
  
  
  RESULTS
  Reasonable agreement was observed between the experimentally measured and the finite element calculated torques, confirming the validity of our finite element simulation, which showed that high stresses can develop in the interfacial bone during microimplant insertion. Hoop stresses above the ultimate tensile strength and radial stresses above the ultimate compressive strength of cortical bone developed in the bone. Furthermore, residual radial stresses higher than the critical threshold stress to trigger pathologic bone resorption were observed after insertion. These high insertion-related stresses implied that it is not the orthodontic force or the timing of its application, but the insertion conditions that can determine the bone's response to the microimplant and its clinical prognosis.
  
  
  CONCLUSIONS
  This in-vitro finite element analysis showed that, during the self-tapping insertion of orthodontic microimplants, stresses high enough to fracture cortical bone can develop. After the self-tapping insertion, the radial stresses calculated at the interfacial bone were higher than the threshold value to trigger pathologic bone resorption.
authors.affiliation: Department of Orthodontics, School of Dentistry, Kyungpook National University, Daegu, Korea.
authors.forename: Wonjae
authors.initials: W
authors.lastname: Yu
authors.forename: Hyo-Sang
authors.initials: HS
authors.lastname: Park
authors.forename: Hee-Moon
authors.initials: HM
authors.lastname: Kyung
authors.forename: Oh-Won
authors.initials: OW
authors.lastname: Kwon
mesh_terms: D000497:Alloys; D000818:Animals; D003722:Dental Alloys; D003758:Dental Implantation, Endosseous / Q000379:methods; D017267:Dental Prosthesis Design; D003799:Dental Stress Analysis; D020342:Finite Element Analysis; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation* / Q000379:methods*; D011817:Rabbits; D013977:Tibia / Q000601:surgery; D014025:Titanium
chemical_list: D000497:Alloys; D003722:Dental Alloys; C031462:titanium alloy (TiAl6V4); D014025:Titanium