Root canal instruments are poorly standardized.

In an earlier study we demonstrated that root canal instruments vary greatly in their effectiveness in removing substrates. To further analyze the reason for this variation of results, the dimensions of the instruments used were considered of interest as their matching effectiveness may be size dependent. Nine different brands of Hedstrom files, seven brands of K files, and four brands of special files were examined. The measurements were done in a computerized measuring microscope and the data were compared with earlier reported data on machining. Although the dimensions of the instruments varied greatly, no correlation could be found between the machining and dimensions. Only one brand of files was completely within allowable size range.