title: [Deformation evaluation of ProTaper nickel-titanium rotary instruments in curved canals instrumentation in vitro].
abstract: OBJECTIVE
  To evaluate the deformation of ProTaper rotary instruments using in root canals of different curvature in vitro.
  
  
  METHODS
  Extracted first mandibular molars were divided into two experimental groups according to the curvature of mesial buccal canals: group A with moderate curvature and group B with severe curvature. Only the mesial buccal canals of all these teeth were prepared with 6 sets of new ProTaper rotary instruments individually. Additionally, the control group was established with a set of new ProTaper rotary instruments. After finishing each canal preparation, the instruments accompanied by control were examined under the stereomicroscope by an inspector without knowing the group. If distortion, unwinding, abrasion or fracture occurred within one set of instruments, then the whole set was disposed. The sets without problems were in use until 30 times. After 5, 10, 20 times canal preparation, S1, F1 files without deformation under stereomicroscope were examined under scanning electron microscope (SEM).
  
  
  RESULTS
  Deformation of ProTaper rotary instruments happened after 12 times in group A and after 7 times in group B. In these two experimental groups, microcracks were found increasing with the times of use under SEM in the instruments without deformation under stereomicroscope. The microcracks on tip of instruments were deep in the early use and became smoother after 10 times. Similar changes happened on knife-edge of instruments, and the microcracks extended over the edge after 20 times use.
  
  
  CONCLUSIONS
  Root canals with severe curvature tend to damage ProTaper rotary instruments more frequently than moderately curved canals. ProTaper rotary instruments are appropriate to treat less than 7 root canals with severe curvature or 12 root canals with moderate curvature. Stereomicroscope is recommended to detect early damages on Ni-Ti rotary instruments, for preventing instruments fracture in clinic.
authors.affiliation: Department of Special Diagnosis, School and Hospital of Stomatology, Peking University, Beijing 100081, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Yan
authors.forename: Min
authors.initials: M
authors.lastname: Ren
authors.forename: Xing-Zhe
authors.initials: XZ
authors.lastname: Yin
authors.forename: Shu-Yan
authors.initials: SY
authors.lastname: Zhao
authors.forename: Cheng-Fei
authors.initials: CF
authors.lastname: Zhang
mesh_terms: D001641:Bicuspid; D003722:Dental Alloys; D003762:Dental Instruments; D003786:Dental Pulp Cavity; D006801:Humans; D066298:In Vitro Techniques; D008963:Molar; D009532:Nickel; D018915:Root Canal Preparation; D014025:Titanium
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium