title: Resistance to flexural fatigue of Reciproc R25 files under continuous rotation and reciprocating movement.
abstract: BACKGROUND
  The aim of the present work was to evaluate the resistance to flexural fatigue of Reciproc R25 nickel-titanium files, 25 mm, used in continuous rotation motion or reciprocation motion, in dynamic assays device.
  
  
  METHODS
  Thirty-six Reciproc R25 files were divided into 2 groups (n = 18) according to kinematics applied, continuous rotary (group CR) and reciprocation motion (group RM). The files were submitted to dynamic assays device moved by an electric engine with 300 rpm of speed that permitted the reproduction of pecking motion. The files run on a ring's groove of temperate steel, simulating instrumentation of a curved root canal with 40° and 5 mm of curvature radius. The fracture of file was detected by sensor of device, and the time was marked. The data were analyzed statistically by Student's t test, with level of significance of 95%.
  
  
  RESULTS
  The instruments moved by reciprocating movement reached significantly higher numbers of cycles before fracture (mean, 1787.78 cycles) when compared with instruments moved by continuous rotary (mean, 816.39 cycles).
  
  
  CONCLUSIONS
  The results showed that the reciprocation motion improves flexural fatigue resistance in nickel-titanium instrument Reciproc R25 when compared with continuous rotation movement.
authors.affiliation: Department of Restorative Dentistry, School of Dentistry, Universidade de São Paulo, São Paulo, Brazil. ggavini@usp.br
authors.forename: Giulio
authors.initials: G
authors.lastname: Gavini
authors.forename: Celso Luiz
authors.initials: CL
authors.lastname: Caldeira
authors.forename: Eduardo
authors.initials: E
authors.lastname: Akisue
authors.forename: George Táccio de Miranda
authors.initials: GT
authors.lastname: Candeiro
authors.forename: Dirce Akemi Sacaguti
authors.initials: DA
authors.lastname: Kawakami
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009068:Movement; D009532:Nickel / Q000737:chemistry*; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium