A dentinal shoulder with a smooth surface is necessary to ensure accurate adaptation of a porcelain crown. The surface roughness of dentinal shoulders prepared with different instruments was investigated in this in vitro study. Sixty shoulders, 1 mm wide, were prepared with coarse grit diamonds in extracted formalin-stored teeth. Of these 60 shoulders 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 surfaces were further finished and refined with a hand chisel, and the other 30 surfaces were finished with a flat-ended diamond tip held in an ultrasonic generating device; the Ra was then recorded. These shoulder preparations were examined under a scanning electron microscope. The Ra 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 the Ra (p < 0.05). Scanning electron micrographs revealed no apparent qualitative differences between surface roughness of the shoulders prepared by the diamonds or by the hand-planed surface. However, deeper scratches were evident at ultrasonically planed surfaces.