Abstract: Objective To investigate the incidence of C-shaped root canal system in mandibular second molars on native people of Shandong. Methods Use epidemiological investigation method and choose native people more than 18 years old of Shandong as study objects. After filming the X-ray of mandibular second molars, the incidence of C-shaped root canal system is verdicted according to its radiographic features. Results This study includes 1 752 mandibular second molars of 879 study objects. The number of mandibular second molars with Cshaped root canal system is 471 and the incidence is 26.88%. Conclusion The incidence of C-shaped root canal system in mandibular second molars is very high on native people of Shandong and it has an important clinical signification to study its anatomic configurations.

Key words: C-shaped root canal system, mandibular second molar, X-ray feature, incidence