IN VITRO COMPARISON OF THE CUTTING EFFICIENCY AND TEMPERATURE PRODUCTION OF 10 DIFFERENT ROTARY CUTTING INSTRUMENTS. PART I: TURBINE

Statement of problem. Standards to test the cutting efficiency of dental rotary cutting instruments are either nonexistent or inappropriate, and knowledge of the factors that affect their cutting performance is limited. Therefore, rotary cutting instruments for crown preparation are generally marketed with weak or unsupported claims of superior performance. Purpose. The purpose of this study was to examine the cutting behavior of a wide selection of rotary cutting instruments under carefully controlled and reproducible conditions with an air-turbine handpiece. Material and methods. Ten groups of rotary cutting instruments (n=30) designed for tooth preparation were selected: 9 diamond rotary cutting instruments (7 multi-use, 2 disposable) and 1 carbide bur. One bur per group was imaged with a scanning electron microscope (SEM) at different magnifications. Macor blocks (n=75) were used as a substrate, and 4 cuts were made on each specimen, using a new rotary cutting instrument each time, for a total of 300 cuts. The cuts were performed with an air-turbine handpiece (Midwest Quiet Air). A computer-controlled, custom-made testing apparatus was used to monitor all sensors and control the cutting action. The data were analyzed to compare the correlation of rotary cutting instrument type, grit, amount of pressure, cutting rate, revolutions per minute (rpm), temperature, and type of handpiece, using 1-way ANOVA and Tukey's Studentized Range test (alpha=.05). Results. Compared to the baseline temperature, all rotary cutting Instruments showed a reduction of temperature in the simulated pulp chamber. The Great White Ultra (carbide bur) showed a significantly higher rate of advancement (0.15 mm/s) and lower applied load (106.46 g) and rpm (304,375.97). Conclusions. Tooth preparation with an adequate water flow does not cause harmful temperature changes in the pulp chamber, regardless of rotary cutting instrument type. The tested carbide bur showed greater cutting efficiency than all diamond rotary cutting instruments. (J Prosthet Dent 2009;101:248-261)