[Effect of the action of rotary diamond instruments on the enamel and dentine. Scanning electron microscopic study].

Mesio-occluso-distal cavities were prepared "in vitro" on human teeth using cylindrical diamond instruments of fine granulometry and operating at high and very high speeds. The surface states obtained on enamel and dentine were examined with scanning electron microscopy. The striae produced by these instruments appeared as well marked straight ridges and depressions the depths of which were higher than those produced by steel and tungsten carbide burs. Along cavo-surface angles, superficial prism fractures and/or border irregularities were visible, especially in relation to the cutting plane orientation versus the prism axes. A highly adhering smear layer on enamel walls was observed. The rotational direction of the diamond instruments did not appear to affect the quality of the cavo-surface box angles as it did for steel and tungsten carbide burs.