title: Effect of altering the reciprocation range on the fatigue life and the shaping ability of WaveOne nickel-titanium instruments.
abstract: BACKGROUND
  The purpose of this study was to investigate the effect of altering the reciprocation range of the WaveOne instrument (Dentsply Maillefer, Ballaigues, Switzerland) on its fatigue life and shaping ability regarding tendency for canal transportation, the canal centering ratio, and preparation time.
  
  
  METHODS
  Thirty primary WaveOne instruments were divided into 3 equal groups according to the reciprocation range used: G1: 150 counterclockwise (CCW)-30 clockwise (CW), G2: 120 CCW-30 CW, and G3: 90 CCW-45 CW. They were activated in a cyclic fatigue testing device until fracture. The time to fracture and the length of the fractured tip were recorded and registered. To assess the shaping ability, 30 mesiobuccal canals of mandibular molars were prepared using the same reciprocation ranges. Canals were scanned using cone-beam computed tomography scanning before and after preparation to evaluate root canal transportation and the canal centering ratio at 1, 4, and 7 mm from the apex. The time taken to complete canal preparation was also recorded. The mean ± standard deviation values were analyzed using analysis of variance and the Tukey post hoc test. The significance level was set at P < .05.
  
  
  RESULTS
  The time to fracture recorded increased as the reciprocation range decreased, and this was significant for the 90 CCW-45 CW group (P < .05). Regarding preparation time, it increased significantly as the reciprocation range was decreased (P < .05). Results for canal transportation and the canal centering ratio showed that at 1 mm from the apex there were no significant differences between the experimental groups. For the other studied levels, the 150 CCW-30 CW group had the highest mean for canal transportation and the lowest mean for the canal centering ratio, which was statistically significant in comparison with the other experimental groups (P < .05).
  
  
  CONCLUSIONS
  Decreasing the reciprocation range of WaveOne instruments resulted in an increased cyclic fatigue resistance with less canal transportation and more centered preparations but with longer preparation times.
authors.affiliation: Department of Endodontics, Ain Shams University, Cairo, Egypt. Shehab007@yahoo.com
authors.forename: Shehab El Din Mohamed
authors.initials: Sel D
authors.lastname: Saber
authors.forename: Shaimaa Mohamed
authors.initials: SM
authors.lastname: Abu El Sadat
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods; D003722:Dental Alloys / Q000737:chemistry*; D003786:Dental Pulp Cavity / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008422:Materials Testing; D008963:Molar / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D009532:Nickel / Q000737:chemistry*; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*; D019227:Tooth Apex / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D019415:Torque
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium