title: Progressive versus constant tapered shaft design using NiTi rotary instruments.
abstract: OBJECTIVE
  To evaluate the influence of a progressive versus constant tapered shaft design on canal preparation by NiTi rotary techniques.
  
  
  METHODS
  A XMCT-scanner and custom-made software were used to nondestructively analyse the mesial canals of 10 extracted mandibular molars in 3D with a spatial resolution of 12.5 microm. Specimens (n = 10 per group) were scanned before and after preparation using ProTaper (progressive tapered) or K3 (constant tapered) files. Numerical values for volume, curvature, dentine removal and centring ratio were obtained in addition to a visual inspection for canal aberrations. Data were analysed by (multiway factorial) anova, Wilcoxon tests and t-tests.
  
  
  RESULTS
  The volume of total dentine removal (mean +/- SD) was 1.21 +/- 0.66 mm(3) (ProTaper) and 1.06 +/- 0.23 mm(3) (K3) (P > 0.05), and the amount of dentine removal at all separate horizontal regions examined was comparable for both groups. The mean linear dentine removal (transportation) was in the range of 8-212 microm (ProTaper) and 4-187 microm (K3). The resultant centring ratio varied from 0.01 to 0.24 (ProTaper) and from 0.01 to 0.17 (K3), whilst different straightening patterns were observed. A centre displacement towards the furcation coronally was most pronounced for the ProTaper group whereas a centre displacement towards the outer side of the curvature more apically was only observed for the K3 group. No severe canal aberrations were found.
  
  
  CONCLUSIONS
  The progressive tapered shaft design of the ProTaper instrument was less influenced by the mid-root curvature than the constant tapered design of the K3 instrument thereby providing a good centred apical preparation. However, ProTaper instruments tended to transport towards the furcation in the coronal region.
authors.affiliation: Department of Conservative Dentistry, Leuven BIOMAT Research Cluster, Catholic University of Leuven, Belgium. Lars.Bergmans@med.kuleuven.ac.be
authors.forename: L
authors.initials: L
authors.lastname: Bergmans
authors.forename: J
authors.initials: J
authors.lastname: Van Cleynenbreugel
authors.forename: M
authors.initials: M
authors.lastname: Beullens
authors.forename: M
authors.initials: M
authors.lastname: Wevers
authors.forename: B
authors.initials: B
authors.lastname: Van Meerbeek
authors.forename: P
authors.initials: P
authors.lastname: Lambrechts
mesh_terms: D000704:Analysis of Variance; D003722:Dental Alloys; D003762:Dental Instruments; D003786:Dental Pulp Cavity / Q000648:ultrastructure; D004867:Equipment Design; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008963:Molar; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D018709:Statistics, Nonparametric; D014025:Titanium; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium