title: Constant Insertion Rate Methodology for Measuring Torque and Apical Force in 3 Nickel-Titanium Instruments with Different Cross-sectional Designs.
abstract: BACKGROUND
  The aim of this study was to evaluate the cutting characteristics of 3 nickel-titanium instruments with different cross-sectional designs using a recently developed methodology.
  
  
  METHODS
  Insertion tests at a constant rate of 5.4 mm/min were performed on a bench test device by measuring the torque and apical force required for penetrating prefabricated acrylic blocks containing an artificial canal preflared with #10 and #15 K-files. Size 20/.06 Mtwo (VDW, Munich, Germany) and RaCe (FKG, La-Chaux De Fonds, Switzerland) instruments, together with ProTaper Universal (PTU) F1 instruments (Dentsply Maillefer, Ballaigues, Switzerland) (10 instruments of each type), were tested using an endodontic motor set at 300 rpm and 5 N·cm. The instruments were characterized with respect to the pitch length, rake angle, and cross-sectional area. Statistical analysis was performed with analysis of variance (α = 0.05).
  
  
  RESULTS
  The torque was significantly lower for Mtwo compared with the other 2 groups (P < .05). It was also lower for RaCe in comparison with PTU F1 (P < .05). Regarding the apical force, the RaCe instruments had lower values when compared with the Mtwo and PTU F1 instruments (P < .05). There was no statistically significant difference between the PTU F1 and Mtwo instruments (P > .05).
  
  
  CONCLUSIONS
  The methodology allowed the cutting properties of the instruments to be assessed in terms of their different geometric characteristics. The cross-sectional design, especially in Mtwo instruments with 2 sharp edges and great chip removal capability, was a differential factor for their higher cutting action.
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil; Department of Metallurgical and Materials Engineering, School of Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Isabella Faria da Cunha
authors.initials: IF
authors.lastname: Peixoto
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Érika Sales Joviano
authors.initials: ÉS
authors.lastname: Pereira
authors.affiliation: Department of Metallurgical and Materials Engineering, School of Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Diego Pinheiro
authors.initials: DP
authors.lastname: Aun
authors.affiliation: Department of Metallurgical and Materials Engineering, School of Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil. Electronic address: vbuono@demet.ufmg.br.
authors.forename: Vicente Tadeu Lopes
authors.initials: VT
authors.lastname: Buono
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Maria Guiomar de Azevedo
authors.initials: MG
authors.lastname: Bahia
mesh_terms: D003722:Dental Alloys; D004867:Equipment Design; D006801:Humans; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D014025:Titanium; D019415:Torque
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: Apical force; NiTi instruments; cross-sectional design; rake angle; torque