Scanning electron microscope evaluation of wear of dental curettes during standardized root planing

Root planing relies upon the quality of instrument cutting edges. This study evaluated the sharpness and wear of some dental curettes available in the market following standardized root planing procedures. Nine working edges of nine Gracey No. 1/2 DE curettes, three each from three different manufacturers, were used as controls. These unused factory-sharpened edges were examined by scanning electron microscope (SEM). Eighteen edges of nine curettes of the same brands were likewise examined after root planing procedures. Root planing was carried out on extracted one-rooted teeth mounted in natural positions in manikin jaws. Working areas measuring 3 X 5 mm were marked on root surfaces previously exposed by periodontitis. Root planing procedures included 15 vertical strokes done by either Side 1 or Side 2 of each instrument in relation to a single working area of a tooth, and the same procedure repeated 3 times using the opposite side of the curette. All working edges were examined at points 1 and 2 mm from the tip under 500 times magnification. Edge deformation increased significantly from the control group to the "15-stroke" group and from the "15-stroke" group to the "45-stroke" group. Factory-sharpened curettes (control) were sharp, with functional wire edges present on 55% of the specimens. After 15 strokes, nonfunctional wire edges and narrow edge deformations with bevels measuring less than 15 mu were present. After 45 strokes eight cutting edges (88.9%) showed bevels wider than 15 mu. The difference between the three brands was not significant in any group (i.e., controls, 15 strokes, 45 strokes). Further study is indicated to evaluate the relationships between bevel dimensions and root planing effectiveness.