Merits of soft nitriding scalers.
BACKGROUND
It has been demonstrated that nitriding modifies the physical characteristics of metals. The purpose of this study was to evaluate the changes induced by 3 levels of inexpensive soft nitriding treatments on commercial 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 strokes x 10 and thereafter every 1,000 to 8,000 strokes by an automatic scaling apparatus against epoxy resin. Weight differences were used to indicate abrasion resistance; the relative efficiency (RE) was calculated as the ratio of scaled amount at a given number of strokes (SN/NT). The hardness and the tensile strengths were determined for each soft nitriding treatment level. 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 the SN90 was more efficient than SN30 for the first 100 strokes (P<0.01). The RE of all SN scalers was significantly greater (2.3 to 2.7 times) than the NT scalers from the beginning of the study and throughout all time periods (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 scalers. The untreated scalers' performance decreased to 10% of baseline after 100 strokes; but even after 1,000 strokes, the SN60 and SN90 performed better than new untreated scalers. Thereafter, all scalers' performance, including SN scalers, decreased. While the NT blades ceased to cut measurable amounts 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), the SN60 had the highest tensile strength (P <0.01), suggesting that it might be the safest in practice.


CONCLUSIONS
Sixty minutes of soft nitriding treatment of commercially available taglite scalers seem to be the optimal treatment duration to increase their durability, on the order of 100 to 1,000 times, without jeopardizing safety for clinical use.
Fujimura
T
T
Department of Endodontics and Periodontics, Fukuoka Dental College, Japan. PXI00152@nifty.ne.jp
Nagai
A
A
Kaneko
N
N
Morishita
K
K
Ohta
N
N
Kaya
H
H
D003722:Dental Alloys / Q000737:chemistry*; D003762:Dental Instruments; D012534:Dental Scaling / Q000295:instrumentation*; D004577:Electron Probe Microanalysis; D004867:Equipment Design; D006244:Hardness; D008422:Materials Testing; D017672:Nitrogen Compounds / Q000737:chemistry*; D013232:Steel / Q000737:chemistry; D013718:Tensile Strength; D013997:Time Factors; D014508:Urea
D003722:Dental Alloys; D017672:Nitrogen Compounds; D013232:Steel; D014508:Urea