SURFACE-ROUGHNESS OF TOOTH SHOULDER PREPARATIONS CREATED BY ROTARY INSTRUMENTATION, HAND PLANING, AND ULTRASONIC OSCILLATION

A dentinal shoulder with a smooth surface is necessary to ensure accur ate adaptation of a porcelain crown. The surface roughness of dentinal shoulders prepared with different instruments was investigated in thi s in vitro study. Sixty shoulders, 1 mm wide, were prepared with coars e grit diamonds in extracted formalin-stored teeth. Of these 60 should ers 20 were further refined with fine grit, and 20 more shoulders were refined with super-fine grit diamonds. The surface roughness (Ra) of the dentinal shoulders was recorded after each procedure. Thirty surfa ces were further finished and refined with a hand chisel, and the othe r 30 surfaces were finished with a flat-ended diamond tip held in an u ltrasonic generating device; the Ra was then recorded. These shoulder preparations were examined under a scanning electron microscope. The H a of the dentinal shoulders prepared by the ends of the different grit diamonds was not significantly different (p > 0.05). Hand planing did not improve the Ra, and ultrasonic planing significantly increased th e Ra (p < 0.05). Scanning electron micrographs revealed no apparent qu alitative differences between surface roughness of the shoulders prepa red by the diamonds or by the hand-planed surface, However, deeper scr atches were evident at ultrasonically planed surfaces.