title: Abfraction: 3D analysis by means of the finite element method.
abstract: OBJECTIVE
  Tooth deflections under functional loads are considered to be the etiologic factor of noncarious cervical lesions. There are several studies on the materials used to restore these lesions; however, there are few discussing this phenomenon's etiology from a biomechanic point of view. This study was undertaken to evaluate tooth behavior when forces were applied from different directions.
  
  
  METHODS
  A 3D finite element model of a maxillary central incisor was designed. A distributed force of 1.5 N was applied on the palatal side of the crown in five stages, with varying directions progressing from tipping to intrusion. Two separate approaches (displacement and stress) were considered to evaluate the cervical area from a stress perspective.
  
  
  RESULTS
  The displacement approach resulted in a curved path when compared to a straight line connecting the apical and incisal areas. The maximum deflections were in the cementoenamel junction area. The same area was shown to undergo the maximum of von Mises stress and stress intensity. Patterns of the von Mises stress when evaluated in a mesiodistal direction were in complete agreement with the shape of the cervical lesions (except for the application of the intrusive force, which rules out its effect in producing such lesions).
  
  
  CONCLUSIONS
  Force applications, except for intrusive force, can produce increases in the von Mises stress and tooth deflections that can answer the question of the etiology of noncarious cervical lesions. The highest amounts of deflection and von Mises stress were produced by the 45-degree force application.
authors.affiliation: Department of Orthodontics, Shiraz School of Dental Medicine, Shiraz, Iran. gueramya@yahoo.com
authors.forename: Allahyar
authors.initials: A
authors.lastname: Geramy
authors.forename: Farahnaz
authors.initials: F
authors.lastname: Sharafoddin
mesh_terms: D003198:Computer Simulation; D003739:Dental Cementum / Q000503:physiopathology; D003743:Dental Enamel / Q000503:physiopathology; D020342:Finite Element Analysis; D006801:Humans; D007180:Incisor / Q000503:physiopathology; D008954:Models, Biological; D013314:Stress, Mechanical; D019227:Tooth Apex / Q000503:physiopathology; D019237:Tooth Cervix / Q000503:physiopathology*; D019228:Tooth Crown / Q000503:physiopathology; D014076:Tooth Diseases / Q000209:etiology*