title: Shaping ability of ProTaper NEXT and BT-RaCe nickel-titanium instruments in severely curved root canals.
abstract: OBJECTIVE
  To compare the shaping ability of four different nickel-titanium rotary instruments during the preparation of curved root canals in extracted teeth.
  
  
  METHODS
  A total of 80 root canals with curvatures ranging between 25° and 39° were divided into four groups of 20 canals. Based on radiographs taken prior to instrumentation, the groups were balanced with respect to the angle and the radius of canal curvature. Canals were prepared to a final apical size of 40 using Mtwo, ProTaper Universal, ProTaper NEXT and BT-RaCe. Using pre- and post-instrumentation radiographs, straightening of the canal curvatures and canal transportation were determined with a computer image analysis programme. Preparation time and instrument failures were also recorded. The data were analysed statistically using anova and Student-Newman-Keuls test.
  
  
  RESULTS
  The use of BT-RaCe files resulted in significantly more straightening during instrumentation compared to Mtwo (P < 0.05), whilst the differences between all other instruments were not significant (P > 0.05). No significant differences were obtained between all four instruments regarding canal transportation (P = 0.429). Instrumentation with ProTaper NEXT files was significantly faster than with all other instruments (P < 0.05). During the preparation of the curved canals, one BT2 instrument fractured, whilst no fracture occurred when using the other instruments (P > 0.05).
  
  
  CONCLUSIONS
  Within the parameters of this study, all instruments maintained root canal curvature well and were safe. However, care should be taken when using the BT2 instrument due to its unique cylindrical design.
authors.affiliation: Central Interdisciplinary Ambulance in the School of Dentistry, University of Münster, Münster, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Bürklein
authors.affiliation: Department of Operative Dentistry, University of Münster, Münster, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Mathey
authors.affiliation: Central Interdisciplinary Ambulance in the School of Dentistry, University of Münster, Münster, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Schäfer
mesh_terms: D003722:Dental Alloys; D003762:Dental Instruments; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D066298:In Vitro Techniques; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D014025:Titanium; D019415:Torque
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: M-wire; Mtwo; canal curvature; canal straightening; rotational speed