title: Root canal preparation with FlexMaster: asessment of torque and force in relation to canal anatomy.
abstract: OBJECTIVE
  To investigate physical parameters of FlexMaster nickel-titanium instruments while preparing curved canals in maxillary molars in vitro.
  
  
  METHODS
  A torque-testing platform was used to prepare root canals in 11 extracted human maxillary molars with FlexMaster rotary instruments. Peak torque and force was registered along with numbers of rotations required to shape the canals. Canals were divided into 'wide' and 'constricted' groups depending on canal volumes assessed by microcomputed tomography. Resistance to cyclic fatigue was also tested. Mean scores for each instrument type were calculated and statistically compared using anova and Scheffé post hoc tests.
  
  
  RESULTS
  Mean torque varied between 0.1 +/- 0.1 and 0.8 +/- 0.5 N cm while mean force ranged from 4.2 +/- 2.0 to 7.3 +/- 3.5 N. Mean numbers of rotations totalled up to 18. All three variables registered showed weak correlations to preoperative canal volumes (P < 0.01) and differed significantly between 'wide' and 'constricted' canals (P < 0.001). Numbers of rotations to fracture in a cyclic fatigue test were between 348 and 1362.
  
  
  CONCLUSIONS
  FlexMaster instruments generated low torque scores and were highly resistant to cyclic fatigue, whilst three instruments fractured in extremely narrow canals. Consequently, more research is required to limit fracture incidence and to optimize instrumentation guidelines.
authors.affiliation: Division of Endodontology, Department of Preventive Dentistry, Periodontology and Cariology, University of Zürich, Switzerland.
authors.forename: W
authors.initials: W
authors.lastname: Hübscher
authors.forename: F
authors.initials: F
authors.lastname: Barbakow
authors.forename: O A
authors.initials: OA
authors.lastname: Peters
mesh_terms: D000704:Analysis of Variance; D003722:Dental Alloys; D003762:Dental Instruments; D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D003799:Dental Stress Analysis; D004868:Equipment Failure; D006801:Humans; D008963:Molar; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical; D014025:Titanium; D019415:Torque
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium