Introduction and objective:
In order to archieve good adaptation to the apical diameter, the master gutta-percha (GP) point should match the last instrument used at the working length. The aim of this study was to determine whether the diameters of the standard gutta-percha points comply with the ISO standard.

Material and methods:
The diameter at the tip (D0) of GP points (2% taper) sizes 30, 35 and 40 manufactured by Meta Biomed, South Korea (group A) and DiaDent, South Korea (group B) was assessed using an endodontic gauge (Dentsply Maillefer, Switzerland). The percentage of points larger than ISO size, compliant and smaller than ISO size, was calculated. Data were analysed using the chi2 test, with a significance level of 0.05.

71.2% of assessed points met the ISO size requirements, 16.2% were smaller and 12.6% were larger than expected. These percentages were 76%, 12.6% and 11.4% in group A, and 66.4%, 19.6% and 14% in group B, respectively. There were no statistically significant differences between the percentage of proper and incorrect sizes in groups A and B overall, or for sizes 35 and 40. Only for group A 30 the standardisation of the points was more accurate than for group B 30 (p<0.001).

This study shows that the dimensions of gutta-percha points may differ from the ISO standard. The use of an endodontic gauge can help select points with a good adaptation to the apical diameter and should be introduced as a standard procedure when obturating root canals.

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