title: Evaluating Stress Distribution Pattern in Periodontal Ligament of Maxillary Incisors during Intrusion Assessed by the Finite Element Method.
abstract: BACKGROUND
  The use of miniscrews has expedited the true maxillary incisor intrusion and has minimized untoward side effects such as labial tipping.
  
  
  OBJECTIVE
  The aim of this study was to assess the stress distribution in the periodontal ligament of maxillary incisors when addressed to different models of intrusion mechanics using miniscrews by employing finite element methods. The degree of relative and absolute intrusion of maxillary incisors in different conditions was also evaluated.
  
  
  METHODS
  Finite element model of maxillary central incisor to first premolar was generated by assembling images obtained from a three-dimensional model of maxillary dentition. Four different conditions of intrusion mechanics were simulated with different placement sites of miniscrews as well as different points of force application. In each model, 25-g force was applied to maxillary incisors via miniscrews.
  
  
  RESULTS
  In all four models, increased stress values were identified in the apical region of lateral incisor. Proclination of maxillary incisors was also reported in all the four models. The minimum absolute intrusion was observed when the miniscrew was placed between the lateral incisor and canine and the force was applied at right angles to the archwire, which is very common in clinical practice.
  
  
  CONCLUSIONS
  From the results yield by this study, it seems that the apical region of lateral incisor is the most susceptible region to root resorption during anterior intrusion. When the minimum flaring of maxillary incisors is required in clinical situations, it is suggested to place the miniscrew halfway between the roots of lateral incisor and canine with the force applied to the archwire between central and lateral incisor. In order to achieve maximum absolute intrusion, it is advised to place miniscrew between the roots of central and lateral incisors with the force applied at a right angle to the archwire between these two teeth.
authors.affiliation: Orthodontic Research Center, School of Dentistry, Shiraz University of Medical Sciences, Iran.
authors.forename: Parisa
authors.initials: P
authors.lastname: Salehi
authors.affiliation: Dept. of Orthodontics and Dental Research Center, School of Dentistry, Tehran University of Medical Science, Iran.
authors.forename: Alayar
authors.initials: A
authors.lastname: Gerami
authors.affiliation: Orthodontist, Orthodontic Research Center, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Amirhosein
authors.initials: A
authors.lastname: Najafi
authors.affiliation: Orthodontist, Orthodontic Research Center, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Sepideh
authors.initials: S
authors.lastname: Torkan
keywords: Finite Element Method; Intrusion; Miniscrew