Hardness and strength of endodontic files and reamers

No information could be found in the dental literature on the hardness or strength of the materials in root canal instruments. Hardness testing is a convenient method for examining these products, and strength properties can be deduced from available strength-hardness data. The Vickers hardness of cross-sections of stainless steel root canal files and reamers #15 and #40 made by three well-known manufacturers were determined. Significant differences in hardness were found between manufacturers and between the two sizes of two manufacturers' products. The Vickers hardness range was from 400 to 651, exceeding the range permitted by the AS 1411, and falling below the hardness required for many cutting instruments. The measurements indicate that the instruments are made from high-strength wire. The values obtained suggest that the properties of materials used for some endodontic files could be improved and provide a basis for the selection of superior materials for the future.