title: Fatigue Life of Reciproc and Mtwo instruments subjected to static and dynamic tests.
abstract: BACKGROUND
  This study evaluated the influence of flexibility and reciprocating movement on the fatigue life of endodontic instruments subjected to static and dynamic tests.
  
  
  METHODS
  The rotary nickel-titanium instruments used in this study were Reciproc and Mtwo. The instruments were initially subjected to a cantilever-bending test and then to static and dynamic fatigue tests. Reciproc instruments were operated in reciprocating movement, whereas Mtwo instruments were worked in continuous rotation.
  
  
  RESULTS
  The means of bending resistance (maximum load in grams) of the instruments were 274.9 for Reciproc and 429 for Mtwo. The mean times (in seconds) to fracture of the instruments subjected to static and dynamic tests were 214.5 (static) and 286.3 (dynamic) for Reciproc and 38.9 (static) and 99 (dynamic) for Mtwo. The Student's t test revealed significant differences in all tests (P < .05).
  
  
  CONCLUSIONS
  The results of the present study showed longer fatigue life for instruments with higher flexibility, driven by reciprocating movement, and in the dynamic testing model. These findings reinforce the assumption that use of reciprocating movement is a means to prolong the fatigue life of rotary nickel-titanium endodontic instruments during instrumentation of curved canals.
authors.affiliation: Department of Endodontics, School of Dentistry, Estácio de Sá University, Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Hélio P
authors.initials: HP
authors.lastname: Lopes
authors.forename: Carlos N
authors.initials: CN
authors.lastname: Elias
authors.forename: Márcia V B
authors.initials: MV
authors.lastname: Vieira
authors.forename: José F
authors.initials: JF
authors.lastname: Siqueira
authors.forename: Marcelo
authors.initials: M
authors.lastname: Mangelli
authors.forename: Weber S P
authors.initials: WS
authors.lastname: Lopes
authors.forename: Victor T L
authors.initials: VT
authors.lastname: Vieira
authors.forename: Flávio R F
authors.initials: FR
authors.lastname: Alves
authors.forename: Julio C M
authors.initials: JC
authors.lastname: Oliveira
authors.forename: Thaiane G
authors.initials: TG
authors.lastname: Soares
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; D013997:Time Factors; D014025:Titanium / Q000737:chemistry
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium