The effects of various types of sharpening stones on standard carbon steel Gracey type curets, and the influence of the sharpened curets on periodontally involved root surfaces, during in vitro scaling and root planing, was evaluated by means of scanning electron microscopy (SEM). Six different sharpening stones of varying texture, two of aluminum oxide, two India, and two Arkansas stones were assigned to sharpen six groups of 10 curets each. The curets were first examined under SEM and photographed and all exhibited edge irregularities. They were then sharpened with the different stones and again examined and photographed using SEM. The sharpness of each instrument was graded, related to the type of stone used, and the data compared statistically. A positive correlation was found between the texture of stone used and the surface sharpness it produced on the cutting edge of the instrument. The curets were then used to root plane the root surfaces on periodontally involved, extracted teeth. Replicas of the root surfaces were examined with SEM before and after removal of the smear layer with 10% EDTA. The planed and cleaned root surfaces revealed the effects of the sharpened instruments, with the relative surface roughness of the instrument being imparted to the tooth surface. The curets sharpened with finger grit stones produced smoother surfaces than those sharpened with the rough or coarse grit stone. It may be concluded that the sharpness of curets is related to the type of sharpening stone used and in turn to the smoothness of the planned root.