Effect of rotational speed on the breakage of nickel-titanium rotary files

Nickel-titanium 0.04-tapered rotary flies were evaluated for breakage at di fferent rotational speeds in semicircular bovine bone simulated root canals of identical size and radius for each file size group tested. The bovine b one canals had a radius of curvature of 5 mm and a canal width equivalent t o the Dl diameter of the file plus 0.04 mm, Profile instrument #3, #4, and #5 were tested at 150, 250, and 350 rpm. A contra-angle electric handpiece was mounted on an Instron machine that was set to deliver a constant downwa rd speed of 5 mml min. The electric handpiece and Instron machine were acti vated until the files broke, The amount of file tip penetration into the se micircular bovine bone canal was measured in degrees with a protractor from a radiographic image taken of the file inside the bone model. Greater degr ees of tip penetration indicated greater resistance to breakage. Statistica l analysis was done and the results indicated that there was a significant difference for all file sizes in the extent of file tip penetration before breakage. In the rotation range between 150 and 350 rpm the greatest extent of penetration occurred at 150 rpm. This study concluded that 0.04 taper n ickel-titanium rotary file breakage is less likely to occur if the files ar e rotated at lower speeds.