Comparative analysis of torque and apical force to assess the cutting behaviour of ProTaper Next and ProTaper Universal endodontic instruments.

This study assessed the cutting properties of two Nickel Titanium file systems with different designs and manufacturing materials. ProTaper Next X1 and X2 (PTN; Dentsply Sirona) and ProTaper Universal S2 and F1 (PTU; Dentsply Sirona) instruments were employed. The cutting parameters, that is torque and apical forces, were determined using a specially designed bench-testing machine. Dimensional and geometric parameters were considered to evaluate the results. The average maximum torque values showed statistically significant differences (P < 0.05) among all instruments. Apical force for PTN X2 and PTU F1 instruments initially decreased and then experienced a rapid increase in the last 2 mm of the canal. For PTN X1 and PTU S2, apical force increased during the entire test. When compared to PTU files, PTN required higher torque and apical forces during the shaping procedure. The results lead us to conclude that PTN instruments demonstrated a lower cutting efficiency than PTU.

Enhancement of NiTi superelastic endodontic instruments by TiO2 coating.

Rotary nickel-titanium (NiTi) endodontic instruments were coated with a nanometric flexible TiO2 layer through dip-coating sol-gel. Control groups and coated samples of superelastic NiTi instruments model RaCe 25/0.06 (0.25mm tip-diameter, 6% conicity) were comparatively investigated with respect to the cutting efficiency, fatigue life, and corrosion resistance. Results showed an improvement in cutting efficiency for the coated samples and a high resistance to corrosion in NaClO. The coated instruments showed a better performance in fatigue life after corrosion.

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

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.