Root planing depends on quality instrument cutting edges. The sharpness and wear of stainless steel (SS) and high carbon steel (HCS) dental curettes were compared before and after standardized root planing procedures. Forty working edges of dental curettes, 20 of each alloy, were examined by scanning electron microscope (SEM) prior to any root planing (control), after 15 strokes, and after 45 strokes. Root planing was carried out on freshly extracted, single-rooted teeth, mounted in natural positions in mannikin jaws. Working areas measuring 3 x 5 mm were marked on root surfaces previously exposed by periodontitis. Each working edge was examined at points 1 mm and 2 mm from the tip under the same magnification (x 240). Microscopic observations showed that edge deformation increased from the control (factory sharpened) group, to the "15 stroke" group, and from the "15" to the "45 stroke" group, in both SS and HCS curettes. SS curettes, however, demonstrated significantly more wear than HCS curettes. After 45 strokes, only 5% of the SS curettes were sharp, compared to 20% of the HCS curettes. While 65% of the SS curettes showed severe edge deformation by the end of the study, only 20% of the HCS curettes were severely deformed (P less than 0.01). The results indicate that HCS curettes are more resistant to wear than SS curettes. Further study is indicated to evaluate the relationship between actual bevel dimensions and root planing effectiveness.