[Scanning electron microscopy study of the effect of steel and tungsten carbide burs on dental tissues]. / Etude en microscopie électronique à balayage de l'effet des fraises en acier et en carbure de tungstène sur les tissus dentaires.

The effects of steel and tungsten carbide burs have been studied under the scanning electron microscope on human enamel and dentin during preparation of mesio-occluso-distal cavities in vitro with cutting speeds varying from 5 000 to 120 000 r.p.m. All the cavities presented clean and regular walls. However, the final quality of the cavity borders, and in particular the cavo-surface angles of the box walls, was directly related to the speed and rotation direction of the bur. The cavo-surface angles at the gingival planes showed in all cases fractures of the superficial prisms. The cutting character displayed in dentine surfaces were mainly dependent on the orientation of the tubules in relation to the surface of the cavity preparation and the degree of sclerosed dentine. The cavities prepared in the absence of water and air showed the presence of tissue debris nd cracks; their number increased with increasing rotational speed.

[Effect of the action of rotary diamond instruments on the enamel and dentine. Scanning electron microscopic study]. / Effets de l'action d'instruments rotatifs diamantés sur l'émail et la dentine. Etude en microscopie électronique á balayage.

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.