Abstract: A set of instruments is provided for reaming out dental root canals. The instruments of the set are distributed in groups of three having, in each group, a common diameter D1 measured at the root of its terminal point. In each group, the diameter D2 measured at the root of the cutting lips of a conical stem of the instrument is different, from one instrument to the next one of the group. Thus, the conicity of the three instruments of each group increases from one to the next, which enables a practitioner to ream out dental root canals to impart thereto a more wide-mouthed shape than is usually the case, such shape being especially suitable to be sealed by means of gutta-percha.