title: Mini-implant loosening: 3D analysis using the finite element method.
abstract: OBJECTIVE
  Mini-implants are a relatively new device for absolute anchorage control in orthodontics. Their failure due to loosening is a multifactorial problem. Improper positioning of mini-implants with different diameters is evaluated in this study via the finite element method.
  
  
  METHODS
  Twelve 3D finite element models of a mandibular posterior segment were designed and included the first molar, a mini-implant, the periodontal ligament, and spongy and cortical bone. They were similar except for the mini-implant position and diameter (1.3, 1.6, and 2.2 mm). A vertical force of 300 N was applied to the occlusal molar surface. The von Mises stress and energy produced by the applied occlusal forces were assessed in the mini-implant and bone.
  
  
  RESULTS
  The stress findings were between 15.284 and 359.77 MPa for the mini-implants based on their diameters and locations. The mini-implant energy findings were between 0.00084 and 0.258 mJ. These ranges for bone stress and energy changes were 17.611 and 129.45 MPa and 0.296 and 1.575 mJ, respectively.
  
  
  CONCLUSIONS
  A decrease in the distance between the mini-implant and tooth root has a direct effect on different parameters to explain mini-implant loosening.
authors.affiliation: Department of Orthodontics, School of Dental Medicine, Tehran University of Medical Sciences, Tehran, Iran. gueramya@yahoo.com
authors.forename: Allahyar
authors.initials: A
authors.lastname: Geramy
authors.forename: Jean Marc
authors.initials: JM
authors.lastname: Retrouvey
authors.forename: Reza
authors.initials: R
authors.lastname: Jelodar
authors.forename: Hasan
authors.initials: H
authors.lastname: Salehi
mesh_terms: D000539:Alveolar Process; D001732:Bite Force; D003198:Computer Simulation; D015921:Dental Implants; D003799:Dental Stress Analysis; D020342:Finite Element Analysis; D006801:Humans; D013314:Stress, Mechanical
chemical_list: D015921:Dental Implants