Abstract: Mandibular first premolars have complex root canals. Double root canals and three root canals usually happen. Clinicians should be aware of the normal anatomy of root canal system and vigilant about the possibility of canal variation. In this paper, two cases of mandibular first premolars with double (2-2, Verlucci) and three(1-3,Verlucci) root canals were reported. The root canal type and its incidence were discussed. Clinicians should carefully explore to confirm the existence of variation and avoid missed canals, which are necessary for a successful root canal therapy.

Key words: Mandibular first premolar, Canal variation, Root canal