title: Shaping ability of reciprocating motion in curved root canals: a comparative study with micro-computed tomography.
abstract: BACKGROUND
  Recently, root canal shaping with reciprocating motion has been postulated to reduce the possibility of unexpected file fractures. However, there has been little information on the shaping capability of this reciprocating motion preparation technique. Therefore, the purpose of this study was to evaluate the shaping ability of reciprocating motion when compared with continuous rotation motion in curved root canals.
  
  
  METHODS
  The mesiobuccal and distobuccal canals of 20 extracted maxillary molars with curvatures of 20-45 degrees were instrumented with a series of ProTaper rotary files. The canals in the continuous rotation motion (CM) group (n = 20) were prepared by using continuous rotation with pecking motion, whereas the canals in the reciprocating motion (RM) group (n = 20) were prepared with reciprocating motion (clockwise 140 degrees and counterclockwise 45 degrees). Basic geometric parameters such as curvature, root canal volume, surface area, and structure model index (SMI) before and after canal shaping were evaluated by using micro-computed tomography. The degrees and directions of transportation were also measured, and statistical analysis was carried out with one-way analysis of variance and Tukey post hoc tests.
  
  
  RESULTS
  There were no significant differences between the 2 groups in canal curvature, volume, surface area, and SMI categories measured before preparation (P > .05). Changes in curvature, root canal volume, surface area, and SMI were not affected by the instrumentation technique used (P > .05). There were no significant differences in the degrees and directions of transportation between CM and RM groups (P > .05).
  
  
  CONCLUSIONS
  The application of reciprocating motion during instrumentation did not result in increased apical transportation when compared with continuous rotation motion, even in the apical part of curved canals. Reciprocating motion might be an attractive alternative method to prevent procedural errors during root canal shaping.
authors.affiliation: Department of Conservative Dentistry, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Korea.
authors.forename: Sung-Yeop
authors.initials: SY
authors.lastname: You
authors.forename: Hyeon-Cheol
authors.initials: HC
authors.lastname: Kim
authors.forename: Kwang-Shik
authors.initials: KS
authors.lastname: Bae
authors.forename: Seung-Ho
authors.initials: SH
authors.lastname: Baek
authors.forename: Kee-Yeon
authors.initials: KY
authors.lastname: Kum
authors.forename: WooCheol
authors.initials: W
authors.lastname: Lee
mesh_terms: D000704:Analysis of Variance; D003786:Dental Pulp Cavity / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D003799:Dental Stress Analysis; D006801:Humans; D008963:Molar; D009038:Motion; D018915:Root Canal Preparation / Q000379:methods*; D012399:Rotation; D018709:Statistics, Nonparametric; D018677:Tooth Injuries / Q000517:prevention & control*; D055114:X-Ray Microtomography