title: [The role of occlusal factors in the occurrence of vertical root fracture].
abstract: OBJECTIVE
  To investigate the occlusal characteristics and the condition of tooth abrasion in patients with vertical root fracture and to discuss the etiology of the vertical root fracture and the relationships between occlusal disorder, tooth abrasion and vertical root fracture of molars.
  
  
  METHODS
  Two hundred and seventy-seven cases of root fracture patients were included in the study, with 309 involved teeth. The periodontal status, occlusal wear, occlusal contact area, occlusal interference, occlusal trauma and the X-ray film were observed and evaluated. All statistical analyses were performed using SPSS13.0 software package. Date was expressed as n(%).Differences between groups were compared using X(2) test with SPSS 13.0 software package.
  
  
  RESULTS
  Vertical root fracture occurred in patients aging 40 to 60 years, the first molar mesial root or buccal root was mostly involved. Periodontal tissue destruction was significantly greater than roots without vertical fracture, with formation of localized periodontal pocket. Severe occlusal surface wear, high and steep non-work tip, working tip abrasion, deep occlusal surface concave and lower distal edge were seen in the affected teeth.The degree of vertical root fracture was related to the site of deep occlusal surface concave. Occlusal interference or occlusal trauma was the predisposing factors of vertical root fracture.
  
  
  CONCLUSIONS
  Vertical root fracture is associated with malocclusion and tooth abrasion. Changes of occlusion leads to over occlusal force and abnormal direction of occlusal force, which may be important factor of vertical root fracture.
authors.affiliation: Department of VIP, Changsha Hospital of Stomatology, Changsha 410005, Hunan Province, China. 1489914892@qq.com
authors.forename: Li-xia
authors.initials: LX
authors.lastname: Dai
authors.forename: Wan-liang
authors.initials: WL
authors.lastname: Tong
authors.forename: Jin-ling
authors.initials: JL
authors.lastname: Guo
mesh_terms: D000375:Aging; D001732:Bite Force; D003766:Dental Occlusion; D006801:Humans; D008310:Malocclusion; D008963:Molar; D014082:Tooth Fractures; D014092:Tooth Root / Q000293:injuries*