title: Cyclic fatigue resistance of two nickel-titanium rotary instruments in interrupted rotation.
abstract: OBJECTIVE
  To investigate the influence of interrupted rotation on cyclic fatigue of two nickel-titanium rotary instruments.
  
  
  METHODS
  Cyclic fatigue of 300 new ProTaper Next size X1; X2 and Mtwo size 10, .04 taper; size 15, .05 taper; size 20, .06 taper and size 25, .06 taper instruments was tested in continuous or interrupted rotation. Fifty files of the same brand and size were randomly assigned to five groups (n = 10). Group 1 instruments were tested in continuous rotation; groups 2 and 3 in paused rotation for 1 s every 10 or 20 s, respectively; groups 4 and 5 in interrupted rotation for 5 s every 10 or 20 s, respectively. Cyclic fatigue was expressed in time to fracture (TtF) in an artificial canal with 60° angle and 5 mm radius of curvature. The fracture surface was examined with a scanning electron microscope (SEM). Data were evaluated by two-way analysis of variance.
  
  
  RESULTS
  Cyclic fatigue of groups 2 and 4 of ProTaper Next X2 and Mtwo size 25, .06 taper was significantly lower than that of group 1 of the same instruments (P < 0.01). ProTaper Next X2 had significantly reduced cyclic fatigue in groups 3 and 5 (P < 0.05). No differences were found by interrupting the rotation for 1 or 5 s in all instruments (P > 0.05). Fatigue of other instruments was not affected by interrupted rotation (P > 0.05).
  
  
  CONCLUSIONS
  Interrupted rotation reduced cyclic fatigue resistance of ProTaper Next X2 and Mtwo size 25, .06 taper, especially when a higher number of interruptions was performed.
authors.affiliation: Department of General Surgery and Surgical-Medical Specialties, University of Catania, Catania, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Pedullà
authors.affiliation: Department of Conservative Dentistry, Dental School, Messina University, Messina, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Lizio
authors.affiliation: Department of General Surgery and Surgical-Medical Specialties, University of Catania, Catania, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Scibilia
authors.affiliation: Catholic University of Sacred Heart, Rome, Italy.
authors.forename: N M
authors.identifier: http://orcid.org/0000-0003-3407-9768
authors.initials: NM
authors.lastname: Grande
authors.affiliation: C.L.I.D., "La Sapienza", University of Rome, Isernia, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Plotino
authors.affiliation: MATIS Institute of Microelectronics and Microsystems, National Research Council, Catania, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Boninelli
authors.affiliation: Department of General Surgery and Surgical-Medical Specialties, University of Catania, Catania, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Rapisarda
authors.affiliation: Department of Conservative Dentistry, Dental School, Messina University, Messina, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Lo Giudice
mesh_terms: D003762:Dental Instruments / Q000592:standards*; D009532:Nickel; D012399:Rotation; D014025:Titanium
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: Mtwo; NiTi fracture; ProTaper Next; cyclic fatigue resistance; interrupted rotation