Merits of soft nitriding scalers

Background: It has been demonstrated that nitriding modifies the physical c haracteristics of metals. The purpose off this study was to evaluate the ch anges induced by 3 levels of inexpensive soft nitriding treatments on comme rcial sickle scalers. Methods: Taglite scalers (NT) were soft nitrided for 30 (SN30), 60 (SN60), or 90 (SN90) minutes. The cumulated scaled material was weighed every 10 st rokes x 10 and thereafter every 1,000 to 8,000 strokes by an automatic scal ing apparatus against epoxy resin. Weight differences were used to indicate abrasion resistance; the relative efficiency (RE) was calculated as the ra tio of scaled amount at a given number of strokes (SN/NT). The hardness and the tensile strengths were determined for each soft nitriding treatment le vel. The nitrided layer thickness of representative SN scalers was observed by electron probe x-ray microanalysis. Results: The SN60 was not significantly different from SN30 or SN90, but th e SN90 was more efficient than SN30 for the first 100 strokes (P <0.01). Th e RE of all SN scalers was significantly greater (2.3 to 2.7 times) than th e NT scalers from the beginning of the study and throughout all time period s (SN90 > SN60 > SN30); it increased further during the first 100 strokes ( 9.7 to 15.5 times), indicating the NT scalers wore out faster than SN scale rs. The untreated scalers' performance decreased to 10% of baseline after 1 00 strokes; but even after 1,000 strokes, the SN60 and SN90 performed bette r than new untreated scalers. Thereafter, all scalers' performance, includi ng SN scalers, decreased. While the NT blades ceased to cut measurable amou nts after 7,000 to 8,000 strokes, all SN scalers continued to cut. Although SN90 scalers had the thickest soft layer and were the hardest (P <0.01), t he SN60 had the highest tensile strength (P <0.01), suggesting that it migh t be the safest in practice. Conclusions: Sixty minutes of soft nitriding treatment of commercially avai lable taglite scalers seem to be the optimal treatment duration to increase their durability, ion the order of 100 to 1,000 times, without jeopardizin g safety for clinical use.