In vitro comparison of the cutting efficiency and temperature production of ten different rotary cutting instruments. Part II: electric handpiece and comparison with turbine.

STATEMENT OF PROBLEM

The cutting behavior of dental rotary cutting instruments is influenced by the handpiece used. While the turbine handpiece has been extensively tested in previous studies, limited published information exists on the use of rotary cutting instruments with the electric handpiece system and on possible interactions between rotary cutting instruments and handpiece type.

PURPOSE

The purpose of this study was to examine the cutting performance of a wide selection of rotary cutting instruments tested with the electric handpiece and compare the results with those of the air-turbine handpiece (Part I), identifying possible interactions between handpiece type and rotary cutting instruments.

MATERIAL AND METHODS

Ten groups of rotary cutting instruments (n=30) designed for tooth preparation were selected: 9 diamond (7 multi-use, 2 disposable) and 1 carbide. 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 electric handpiece (Intramatic Lux K200), with the same methods used in the Part I study. To qualitatively evaluate the rotary cutting instrument surface characteristics, 1 specimen from each group was examined 3 times with a scanning electron microscope (SEM): before use, then after use, but before being cleaned and sterilized, and finally, after ultrasonic cleaning. To compare rotary cutting instrument performance between the turbine and electric handpieces, the data were analyzed using 2-way ANOVA to study the main effects of the group of rotary cutting instruments, handpieces, and their interaction. For analysis of the significant main effect, 1-way ANOVA and Tukey's Studentized Range test were used (alpha=.05).

RESULTS

Compared to the baseline temperature, all rotary cutting instruments showed a reduction of the temperature in the simulated pulp chamber when tested with the electric handpiece. The Great White Ultra (carbide bur) showed the highest rate of advancement (0.17 mm/s) and lowest applied load (108.35 g). Considering all rotary cutting instruments as a single group, the electric handpiece showed mean lower temperature (26.68 degrees C), higher rate of advancement (0.12 mm/s), and higher load (124.53 g) than the air-turbine handpiece (28.37 degrees C, 0.11 mm/s, and 121.7 g, respectively). Considering each single group of rotary cutting instruments, significant differences were found for the electric or air-turbine handpiece.

CONCLUSIONS

The tested carbide bur showed greater cutting efficiency than the tested diamond rotary cutting instruments when used with the electric handpiece. The electric handpiece showed a higher cutting efficiency than the turbine, especially when used with the carbide bur, probably due to its greater torque.