Bz. Laufer et al., SURFACE-ROUGHNESS OF TOOTH SHOULDER PREPARATIONS CREATED BY ROTARY INSTRUMENTATION, HAND PLANING, AND ULTRASONIC OSCILLATION, The Journal of prosthetic dentistry, 75(1), 1996, pp. 4-8
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.