title: [Evaluation of the shaping ability of four Ni-Ti rotary instruments in the preparation of simulated curved root canals].
abstract: OBJECTIVE
  To evaluate the effect of four Ni-Ti rotary instruments on the preparation of L-shaped resin root canals.
  
  
  METHODS
  40 L-shaped resin root canals (curvature=38.5°) were divided randomly into four groups: Hero642,Protaper, K3 and Mtwo. Resin root canals were prepared according to the protocols. Preparation time was recorded. Original and postoperative canal images were scanned and superimposed. The preparation effect was evaluated by computer software, such as resin removal amount in inner and outer wall of root canals, change of curvature degree and radius, etc. The data was analyzed with SPSS13.0 software package.
  
  
  RESULTS
  The preparing time of K3 was the longest. Mtwo was the shortest(P<0.05). Resin removal amount showed significant difference among the four instruments in inner root canal wall at BC, O and HO as well as in outer root canal wall at AC, HO and O. Protaper achieved the largest tapered canal,but was the worst for centering ability in the bend. Apical transportation increased near to apical foramen. The four Ni-Ti rotary instruments showed no significant difference regarding safety, undesirable shape, change of root canal's curvature degree and radius except two instrument fracture cases (K3 and Protaper) and two step cases(K3). Postoperative working length tended to be shorter,and root canals were straightened.
  
  
  CONCLUSIONS
  Mtwo prepares simulated resin curved root canals fast. Postoperative root canal's taper by Protaper is significantly larger than Hero642. The 4 Ni-Ti rotary instruments perform good cutting ability and keep root canal's original curvature well.
authors.affiliation: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu 610041, Sichuan Province, China. aiqinhai48@163.com
authors.forename: Yan-yan
authors.initials: YY
authors.lastname: Duan
authors.forename: Ning
authors.initials: N
authors.lastname: Hu
authors.forename: Zhe
authors.initials: Z
authors.lastname: Jiang
authors.forename: Xi-mei
authors.initials: XM
authors.lastname: Xiao
authors.forename: Qin
authors.initials: Q
authors.lastname: Su
mesh_terms: D003786:Dental Pulp Cavity; D006801:Humans; D009532:Nickel; D018915:Root Canal Preparation; D012390:Root Canal Therapy; D014025:Titanium
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium