title: [The effect of curvature of simulated root canal and location of fragment on removal of broken file from simulated root canal].
abstract: OBJECTIVE
  To evaluate effect of root canal curvature and location of the fragment on the removal of broken file from root canal.
  
  
  METHODS
  Sixty extracted mandibular premolars were divided equally into six groups according to location of fragment (2 mm or 8 mm below root canal orifice) and root canal curvature (20 degrees, 30 degrees or 40 degrees). Broken files were removed using ultrasonic tips combined with dental operating microscope. Number of successfully removed case and operating time were recorded. Pre- and post-operative digital radiographs were input into image analyzing software to calculate diameter variance of root canal at the level of tip of broken file.
  
  
  RESULTS
  All the 6 groups of broken files were successfully removed with out perforation. Among same fragment location groups, diameter variance was increased in greater curvature groups and the difference was significant (P < 0.05), while operation time was not significantly different (P > 0.05). Among same root canal curvature groups, the deeper the fragment, the longer operation time, difference being significant (P < 0.05), while difference of diameter variance was not significant (P > 0.05).
  
  
  CONCLUSIONS
  The more curvature of root canal, the more dentine removal amount at the level of broken file tip. Location of fragment has no effect on dentine removal amount. Safe straight-line access and adequate thickness of dentine are essential to removal of broken file from root canal.
authors.affiliation: Dept of Endodontics, Beijing Stomatological Hospital, Capital Medical University, Beijing 100050, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Fu
authors.forename: Ben-Xiang
authors.initials: BX
authors.lastname: Hou
authors.forename: Zhi-Ling
authors.initials: ZL
authors.lastname: Zhang
mesh_terms: D001641:Bicuspid; D003786:Dental Pulp Cavity; D003804:Dentin; D006801:Humans; D018915:Root Canal Preparation; D012390:Root Canal Therapy