Clinical relevance of standardization of endodontic irrigation needle dimensions according to the ISO 9626:1991 and 9626:1991/Amd 1:2001 specification

Aim To examine the current status of standardization of endodontic irrigation needles produced by different manufacturers. Methodiology Measurements of needle internal and external diameter were conducted under scanning electron microscopy and stereoscopic microscopy to determine the incidence and degree of deviation from ISO 9626:1991 and ISO 9626:1991/Amd 1:2001 specification. Results None of the needles examined complied with the ISO nominal size. All SS needles were within the ISO tolerance limits. A Ni-Ti needle, which is not included in the specification, was found to exceed ISO external diameter limits. Conclusions Exact knowledge of the tip's external diameter is crucial for the selection of the appropriate size irrigation probe during endodontic treatment. Units of the widely used 'gauge' system cannot be directly extrapolated to clinical practice. Adoption of millimetre as the standard metric unit, already recommended by ISO, should be accelerated. A colour-coding of needles corresponding to endodontic instruments would also be beneficial.