title: Curved molar root canal preparations using Hero 642 rotary nickel-titanium instruments.
abstract: OBJECTIVE
  The Bramante method was used to study how the natural curvature of root canals was modified when using the Hero 642 nickel-titanium rotary system.
  
  
  METHODS
  Twenty-four canals were selected in freshly extracted human mandibular molars. Every root canal had an angle of curvature greater than 20 degrees. Roots were embedded in clear casting resin using a plaster mould. Cross-sectional cuts were made in the apical, middle and coronal thirds of each root. A first group (control) of 12 curved root canals was prepared using stainless steel hand instruments and the step-back technique. A second group of 12 curved root canals was instrumented using the Hero sequence according to the manufacturer's instructions. For each sectioning level, the amount of dentine removed, the change of shape factor and the canal centre displacement were calculated with the aid of a digital image analysis system. The results were subjected to the Mann-Whitney U-test.
  
  
  RESULTS
  No significant difference occurred in the amount of dentine removed, change of shape factor or canal centre displacement in the coronal and middle thirds of the curved canals. In the apical third, transportation was significantly higher (P=0.0171) with stainless steel hand instruments than with the Hero system.
  
  
  CONCLUSIONS
  The original canal shape was maintained better in the apical third of curved canals when using the Hero system in a crown-down technique when compared to a hand preparation technique with stainless steel instruments.
authors.affiliation: Department of Conservative Dentistry and Endodontics, University of Nice-Sophia Antipolis, France. mfbertra@unice.fr
authors.forename: M F
authors.initials: MF
authors.lastname: Bertrand
authors.forename: L
authors.initials: L
authors.lastname: Lupi-Pégurier
authors.forename: E
authors.initials: E
authors.lastname: Médioni
authors.forename: M
authors.initials: M
authors.lastname: Muller
authors.forename: M
authors.initials: M
authors.lastname: Bolla
mesh_terms: D000328:Adult; D003762:Dental Instruments / Q000592:standards*; D006801:Humans; D008963:Molar; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation* / Q000379:methods; D013193:Stainless Steel; D014025:Titanium
chemical_list: D013193:Stainless Steel; D009532:Nickel; D014025:Titanium