title: Comparison of two canal preparation techniques using mtwo rotary instruments.
abstract: BACKGROUND
  Root canal preparation is an important process in endodontic therapy. Nickel-titanium (NiTi) rotary file system can be used in single length technique (simultaneous technique) without early coronal enlargement, as well as in crown-down method. The purpose of this in vitro study was to compare single length with crown-down methods' shaping ability using Mtwo NiTi files.
  
  
  METHODS
  Fifteen acrylic-resin blocks containing simulated canals were divided into two experimental groups. In group A, single length technique was used and in group B root canals were prepared by crown-down technique. Pre- and post-preparation canals were photographed in a standardized manner and were superimposed. The inner and outer walls of canal curvature were evaluated at three points (apical, middle and coronal) to determine the greatest change. The data was statistically analyzed using the Student t-test by Statistical Analysis System (SAS) software.
  
  
  RESULTS
  Statistical analysis revealed that in group B, dentine was equally removed within the canal coronal to the curvature, whereas in group A, the inner wall was predominantly removed (P<0.01). The two groups had no significant difference at the apical and middle points of the canal curvature.
  
  
  CONCLUSIONS
  Our in vitro study revealed no significant difference between the single length method and crown-down technique using Mtwo for preparation of apical and middle portion of canal curvature.
authors.affiliation: Department of Operative Dentistry, Dental School, Kerman University of Medical Sciences, Kerman, Iran.
authors.forename: Faeze
authors.initials: F
authors.lastname: Hamze
authors.forename: Kiamars
authors.initials: K
authors.lastname: Honardar
authors.forename: Kiumars
authors.initials: K
authors.lastname: Nazarimoghadam
keywords: Curvatures; Instrumentation; Nickel-Titanium; Root Canal Preparation