Introduction
Standardization of endodontic instruments means that hand files and reamers are made to one international set of rules for size number, diameter, taper, length and handle colour, whatever the manufacturer. Thanks to it a size 25 file from any box has the same tip, the gutta-percha and paper points of the same number fit the canal it shaped, and the canal can be enlarged in small, known steps.
Why standardization
Until the late 1950s every manufacturer numbered its instruments in its own way: sizes did not match between brands, the steps between sizes were irregular and filling points did not match the instruments. Ingle and Levine (1958) proposed numbering instruments by their diameter, with a uniform taper, regular size steps and a colour code. These rules are now laid down in ISO 3630-1 and, in the USA, in ANSI/ADA Specification No. 28 (K-type files and reamers) and No. 58 (Hedström files). Standardization gives:
- interchangeable instruments from different manufacturers;
- predictable, gradual enlargement of the canal, size after size;
- matching filling materials: standardized gutta-percha and paper points carry the same sizes and colours;
- minimum quality: dimensional tolerances and resistance to fracture in torsion and bending are tested.