Objective To investigate the association of root canal therapy difficulty with canal anatomic factors in Chinese mandibular permanent incisors. Methods Two hundred and ninety nine Chinese permanent incisors were included in this study. The following anatomic items of the root canal were observed: Root canal length, number of root canal, morphology, curvature, and calcification of pulp chamber and root canal. Based on the root canal therapy evaluation criteria, the root canal therapy difficult scores were assessed. The association of root canal therapy difficulty with canal anatomic factors was analyzed with logistic regression analysis. Results The root canal therapy difficulty grade Ⅰ, grade Ⅱ and grade Ⅲ in Chinese mandibular permanent incisors were 29.4%，20.1% and 50.5%, respectively. The root canal therapy difficulty was significantly associated with the root canal length, number, calcification, and curvature（P
