title: Comparison of the shaping ability of RaCe, FlexMaster, and ProFile nickel-titanium instruments in severely curved root canals.
abstract: BACKGROUND
  Thisin vitrostudy compared the shaping ability of RaCe, FlexMaster, and ProFile rotary nickel-titanium instruments in severely curved root canals of extracted teeth.
  
  
  METHODS
  Sixty maxillary molars with curvatures ranging from 25° to 65° were embedded in a muffle system and portioned into five horizontal sections (thickness 1.2 mm), starting from the apex. Canals were divided into three groups (n = 20, each) and were prepared with RaCe, FlexMaster, or ProFile rotary nickel-titanium instruments and the TriAuto ZX handpiece using a crown-down preparation technique. We evaluated the difference between pre- and postoperative root canal cross-sections, loss of working length, instrument failure, and preparation time. The root canal area before and after the intervention was determined using an area-measuring software. The data were analyzed statistically using a one-way ANOVA followed by a Kruskal-Wallis multiple-comparison Z-value test.
  
  
  RESULTS
  Specimens treated with FlexMaster showed the greatest change from preoperative cross-sections, followed by RaCe and ProFile. The cross-sectional changes induced by RaCe and FlexMaster preparation differed significantly from those produced by ProFile. Loss of working length, instrument failure, and preparation time did not differ significantly between the groups.
  
  
  CONCLUSIONS
  Root canal preparation with the three instruments did not lead to any significant alteration of the original root anatomy or working length. Thus, we conclude that RaCe, FlexMaster, and ProFile instruments are of comparable efficiency and usefulness in the preparation of severely curved root canals.Key words:Endodontics, root canal preparation, rotary, extracted teeth, nickel-titanium.
authors.affiliation: Dr. med. dent, Master of Science Endodontics (M.Sc.), Department of Operative Dentistry, Center for Dentistry and Oral Medicine, Medical Faculty, Goethe University, Frankfurt am Main, Germany.
authors.forename: Lea
authors.initials: L
authors.lastname: Burkhardt
authors.affiliation: Dr. med. dent, Private Practice, Kronberg, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Weidmann
authors.affiliation: Full Professor in Dentistry, Head of Department of Operative Dentistry, Center for Dentistry and Oral Medicine, Medical Faculty, Goethe University, Frankfurt am Main, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Rüttermann
authors.affiliation: PD Dr. med. dent and Master of Medical Education (MME), Department of Operative Dentistry, Center for Dentistry and Oral Medicine, Medical Faculty, Goethe University, Frankfurt am Main, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Gerhardt-Szep