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Constant Insertion Rate Methodology for Measuring Torque and Apical Force in 3 Nickel-Titanium Instruments with Different Cross-sectional Designs

2015; Elsevier BV; Volume: 41; Issue: 9 Linguagem: Inglês

10.1016/j.joen.2015.05.021

1878-3554

Isabella Faria da Cunha Peixoto, Érika Sales Joviano Pereira, Diego Pinheiro Aun, Vicente Tadeu Lopes Buono, Maria Guiomar de Azevedo Bahia,

Dental materials and restorations

Introduction 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.