AbstractThe purpose of this study was to evaluate the spreading of root canal irrigants on human root dentine. The spreading of various solutions on dentine surfaces was measured after pre‐treatment with various conditional solutions. Seven experimental groups were set based on the combination of conditioning solution‐test solution: none‐distilled water; none‐6% sodium hypochlorite (NaOCl); none‐14.3% ethylenediaminetetraacetic acid containing surfactant 0.084% cetrimide (Morhonine®); NaOCl‐NaOCl; NaOCl‐Morhonine®; Morhonine®‐Morhonine® and Morhonine®‐NaOCl. After application of 0.1 mL of conditioning solution for 60 s, 0.5 µL of test solution was placed on dentine surfaces. Spreading of test solution was measured for 480 s to examine the size of the contact area ratio. Those at 300 s were compared among groups using Fisher’s Protected Least Significant Difference (P < 0.05). It was concluded that the contact area ratio of Morhonine®‐NaOCl increased the most significantly among all the experimental groups.