Four-rooted permanent maxillary first and second molars in a northwestern Chinese population

Highlights • We examined the incidence and anatomic features of 4-rooted upper molars in a Chinese population. • The root forms were classified into four types according to the divergence and location of the roots. • A transitional root form between the typical 3-rooted form and double palatal roots was described. • The strategies for clinical management of the extra root and canal.