Hardness and strength of endodontic instruments made from NiTi alloy.

Scant information could be found in the dental literature on the hardness or strength of the materials in nickel-titanium (NiTi) root canal instruments. Hardness testing is a convenient method for examining these products and strength properties can be deduced from strength-hardness data. The Vickers Hardness was determined for NiTi root canal files and reamers from five manufacturers for sizes 15, 25 and 40. Significant differences in hardness were found between manufacturers, with values ranging from 296 to 349. Some differences were found between the different sizes from each manufacturer, but these were generally not statistically significant. These values obtained for NiTi instruments are lower than the softest stainless steel files previously examined (296-347 cf. 403-651), and below the hardness required for many cutting instruments (550-650). The values obtained suggest that NiTi instruments may not be as sharp as, and become blunt more easily than, stainless steel instruments. The strengths are expected to be in the lower range of those for stainless steel instruments.