title: Shaping ability of progressive versus constant taper instruments in curved root canals of extracted teeth.
abstract: OBJECTIVE
  To compare the shaping ability of progressive versus constant taper shaft instruments in curved root canals of extracted human teeth.
  
  
  METHODS
  A total of 40 root canals of mandibular molars with curvatures ranging between 20 degrees and 40 degrees were divided into two groups of 20 canals each and embedded in a muffle system. The root canals sectioned horizontally at three levels before preparation and then remounted into the mould. All root canals were prepared with ProTaper (progressive taper) or Hero Shaper (constant taper) instruments. Pre- and post-instrumentation radiographs and cross-sectional images were obtained. The parameters evaluated were: working safety (instrument failure, apical blockage and loss of working length) and shaping ability (straightening, cross-sectional area, transportation and centring ability). The data were analysed statistically using Student's t-test.
  
  
  RESULTS
  No instrument fractured during preparation. One Hero Shaper instrument permanently deformed. Both instrument systems maintained working length well. The canals prepared with Hero Shaper instruments were straightened to a lesser degree (P < 0.05). ProTaper instruments removed more dentine in the coronal and the middle sections of the canals. Canals prepared with Hero Shaper instruments had less transportation (P < 0.01) and better centring ability (P < 0.05) in the apical section.
  
  
  CONCLUSIONS
  Both instrument systems were safe to use and maintained working length well. The canals prepared with Hero Shaper had less transportation and were better centred in the apical region, possibly because their smaller taper reduced instrument stiffness.
authors.affiliation: Key Laboratory of Oral Biomedical Engineering of Ministry of Education, Sichuan University, Chengdu, China.
authors.forename: G B
authors.initials: GB
authors.lastname: Yang
authors.forename: X D
authors.initials: XD
authors.lastname: Zhou
authors.forename: Y L
authors.initials: YL
authors.lastname: Zheng
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: Y
authors.initials: Y
authors.lastname: Shu
authors.forename: H K
authors.initials: HK
authors.lastname: Wu
mesh_terms: D003786:Dental Pulp Cavity / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D004867:Equipment Design; D004868:Equipment Failure; D004869:Equipment Safety; D006801:Humans; D008963:Molar / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D011859:Radiography; D018915:Root Canal Preparation / Q000295:instrumentation*