title: Alternating versus continuous rotation: a comparative study of the effect on instrument life.
abstract: BACKGROUND
  Rotary nickel-titanium instruments have multiple advantages but with the risk of more fractures because of flexure or torsion. Alternating rotation appears to be an alternative to continuous rotary movement. The objective of this study was to determine the influence of the type of instrument rotation on the frequency of fractures or deformation.
  
  
  METHODS
  Instrumentation was performed on 120 molar root canals with an angle of curvature greater than 30 degrees using alternating rotation (group A: 60 degrees clockwise, 45 degrees counterclockwise) and continuous rotation (group B).
  
  
  RESULTS
  The results indicate that instruments used with alternating rotation have a higher mean number of uses (13.0) compared with the continuous rotation group (10.05); this difference was statistically significant (p < 0.05).
  
  
  CONCLUSIONS
  The ProTaper shaping instruments (S1 and S2) are those that achieved the greatest difference in use with alternating rotation, with S2 being the most resistant to fracture or deformation with the two types of movement used.
authors.affiliation: Department of Operative Dentistry and Endodontics, School of Dentistry, University of Santiago de Compostela, Santiago de Compostela, Spain. puri.varela@usc.es
authors.forename: Purificación
authors.initials: P
authors.lastname: Varela-Patiño
authors.forename: Adalce
authors.initials: A
authors.lastname: Ibañez-Párraga
authors.forename: Berta
authors.initials: B
authors.lastname: Rivas-Mundiña
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Cantatore
authors.forename: Xosé Luis
authors.initials: XL
authors.lastname: Otero
authors.forename: Benjamin
authors.initials: B
authors.lastname: Martin-Biedma
mesh_terms: D003722:Dental Alloys; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004868:Equipment Failure; D006801:Humans; D053208:Kaplan-Meier Estimate; D008963:Molar; D009532:Nickel; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D014025:Titanium; D054159:Torsion, Mechanical
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium