title: Apical stress distribution on maxillary central incisor during various orthodontic tooth movements by varying cemental and two different periodontal ligament thicknesses: a FEM study.
abstract: BACKGROUND
  During fixed orthodontic therapy, when the stress levels in the periodontal ligament (PDL) exceedsan optimum level, it could lead to root resorption.
  
  
  OBJECTIVE
  To determine an apical stress incident on the maxillary central incisor during tooth movement with varying cemental and periodontal ligament thickness by Finite Element Method (FEM) modeling.
  
  
  METHODS
  A three dimensional finite element model of a maxillary central incisor along with enamel, dentin, cementum, PDL and alveolar bone was recreated using EZIDCOM and AUTOCAD software. ALTAIR Hyper mesh 7.0 version was used to create the Finite Element meshwork of the tooth. This virtual model was transferred to Finite Element Analysis software, ANSYS where different tooth movements were performed.
  
  
  METHODS
  Cemental thickness at the root apex was varied from 200 μm to 1000 μm in increments of 200 μm. PDL thickness was varied as 0.24 mm and 0.15 mm. Intrusive, Extrusive, Rotation and Tipping forces were delivered to determine an apical stress for each set of parameters.
  
  
  RESULTS
  Results indicated that an apical stress induced in the cementum and PDL, increased with an increase in cementum and PDL thickness respectively. Apical stress induced in the cementum remained the same or decreased with an increase in the PDL thickness. Apical stress induced in the PDL decreased with an increase in the cementum thickness.
  
  
  CONCLUSIONS
  The study concluded that the clinical delivery of an orthodontic forces will cause stress in the cementum and PDL. Hence, it is necessary to limit the orthodontic force to prevent root resorption.
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Thai Moogambigai Dental College and Hospital, Chennai, India.
authors.forename: N Raj
authors.initials: NR
authors.lastname: Vikram
authors.forename: K S
authors.initials: KS
authors.lastname: Senthil Kumar
authors.forename: K S
authors.initials: KS
authors.lastname: Nagachandran
authors.forename: Y Mohamed
authors.initials: YM
authors.lastname: Hashir
mesh_terms: D000293:Adolescent; D000328:Adult; D000539:Alveolar Process / Q000033:anatomy & histology; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D003739:Dental Cementum / Q000033:anatomy & histology*; D003743:Dental Enamel / Q000033:anatomy & histology; D003782:Dental Pulp / Q000033:anatomy & histology; D003804:Dentin / Q000033:anatomy & histology; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D007180:Incisor / Q000502:physiology*; D008437:Maxilla / Q000502:physiology*; D008954:Models, Biological; D050793:Orthodontic Extrusion / Q000379:methods; D010513:Periodontal Ligament / Q000033:anatomy & histology*; D012399:Rotation; D013314:Stress, Mechanical; D019227:Tooth Apex / Q000502:physiology*; D014087:Tooth Movement Techniques / Q000379:methods*