(PR31) Evaluation of Plastic Deformation in Vortex Blue Nickel-Titanium Instruments After Clinical Use

Abstract: Thermomechanical treatment of Nickel-Titanium (NiTi) rotary instruments causing variations in Austinite and Martensite phase transformation range have gained popularity due to improved mechanical properties. The objective of this study was to evaluate plastic deformation in Vortex Blue (VB) NiTi rotary instruments (Dentsply Sirona, Charlotte, NC) as a change in length, tip diameter at D1, Helical Angle (Ha) at D2, D8, D14 in as-received condition and after single clinical use. VB NiTi rotary instruments 25mm length file set consisting of sizes 25/.04, 30/.04 and 35/.04 were selected from post-graduate endodontic clinics for evaluation (N=10/size). Images of as-received and clinically used files were recorded using a Wild M7 Stereoscope (Leica Microsystems, Buffalo Grove, IL) and a Dino-Lite Digital camera (Torrance, CA). Tip-diameter, file length, and Ha at 2mm, 8mm, and 14mm were measured for dimensional changes between groups and analysed using T-test (p= <0.05). Tip diameters of all file sizes (25/.04, 30/.04, 35/.04) increased significantly with clinical use (p < 0.05). Average Ha at D14 increased significantly in 30/.04 files with clinical use (p < 0.01); while Helical angle at D2 decreased significantly in 35/.04 files. No significant change in length was noted for any file size tested. The results suggest that plastic deformation occurs in endodontic files after a single clinical use. The significant increase in tip diameters may indicate blunting, which decreases efficiency. The increase/decrease in HA for different files may result from stress variation due to root canal anatomy, as well as the location in which each instrument binds.