Wear of nickel-titanium lightspeed instruments evaluated by scanning electron microscopy

Used rotary nickel-titanium instruments require frequent replacing. This laboratory study evaluated defects of Lightspeed cutting tips before and after usage. The instruments were fixed into custom-made holders, the cutting heads photographed in a scanning electron microscope at x120 to x400 magnification at preset points around the cutting tip (90, 180, 270 and 360 degrees) and head-on. Instrument sizes 20 to 32.5, 35 to 60, and 65 to 100 were used in 9, 18, and 36 canals, respectively, and autoclaved after shaping every third root canal. The used instruments were cleaned and then reexamined in a scanning electron microscope as before. The presence of 11 types of conditions was scored from the pre- and postusage photographs. No instruments fractured during the test, but all the cutting heads had one or more imperfections, even before usage. The presence of debris, pitting, and metal strips changed significantly. Imperfections were found on new and used Lightspeed cutting heads, indicating the general difficulty in machining defect-free nickel-titanium rotary instruments. However, high quality should remain a goal to improve instrument efficiency.