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

Used rotary nickel-titanium instruments require frequent replacing. This la boratory study evaluated defects of Lightspeed cutting tips before and afte r usage. The instruments were fixed into custom-made holders, the cutting h eads photographed in a scanning electron microscope at x120 to x400 magnifi cation at preset points around the cutting tip (90, 180, 270 and 360 degree s) and head-on. Instrument sizes 20 to 32.5, 35 to 60, and 65 to 100 were u sed in 9, 18, and 36 canals, respectively, and autoclaved after shaping eve ry third root canal. The used instruments were cleaned and then reexamined in a scanning electron microscope as before. The presence of 11 types of co nditions was scored from the pre- and postusage photographs. No instruments fractured during the test, but all the cutting heads had one or more imper fections, even before usage. The presence of debris, pitting, and metal str ips changed significantly. Imperfections were found on new and used Lightsp eed cutting heads, indicating the general difficulty in machining defect-fr ee nickel-titanium rotary instruments. However, high quality should remain a goal to improve instrument efficiency.