title: Influence of the shape of artificial canals on the fatigue resistance of NiTi rotary instruments.
abstract: OBJECTIVE
  To investigate the influence of the trajectory of NiTi rotary instruments on the outcome of cyclic fatigue tests.
  
  
  METHODS
  Ten ProFile and Mtwo instruments tip size 20, taper 0.06 and tip size 25, taper 0.06 were tested in two simulated root canals with an angle of curvature of 60 degrees and radius of curvature of 5 mm but with different shape. Geometrical analysis of the angle and radius of the curvature that each instrument followed inside the two different artificial canals was performed on digital images. The instruments were then rotated until fracture at a constant speed of 300 rpm to calculate the number of cycles to failure (NCF) and the length of the fractured fragment. Mean values were calculated and analysed using two different multivariate linear regression models and an independent sample t-test.
  
  
  RESULTS
  The shape of the artificial root canal used in cyclic fatigue studies influenced the trajectory of the instrument. This difference is reflected by the NCF measured for the same instrument in the different artificial root canals and by the impact of the type of canal on both the NCF (St.beta = 0.514) and fragment length (St.beta = -0.920).
  
  
  CONCLUSIONS
  Small variations in the geometrical parameters of the curvature of an instrument subjected to flexural fatigue could have a significant influence on the results of fatigue tests.
authors.affiliation: University of Roma 'La Sapienza', Italy. gplotino@fastwebnet.it
authors.forename: G
authors.initials: G
authors.lastname: Plotino
authors.forename: N M
authors.initials: NM
authors.lastname: Grande
authors.forename: M
authors.initials: M
authors.lastname: Cordaro
authors.forename: L
authors.initials: L
authors.lastname: Testarelli
authors.forename: G
authors.initials: G
authors.lastname: Gambarini
mesh_terms: D003722:Dental Alloys; D003762:Dental Instruments; D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D003799:Dental Stress Analysis; D004868:Equipment Failure; D019544:Equipment Failure Analysis; D006801:Humans; D003765:Models, Dental; D009532:Nickel; D012044:Regression Analysis; D018915:Root Canal Preparation / Q000295:instrumentation*; D014025:Titanium
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium