Meterials and Methods: All subjects were patients from department of endodontics, school and hospital of stomatogogy, Shandong University. 1146 mandibular second molars scheduled for root canal therapy were randomly selected and examined from 2004 to 2006. C-shaped canal system were recognized by radiographic and clinical examination. Preoperative radiography was required. Careful clinical examination of pulp chamber and canal entrance followed access under the operative microscope. After probing the root canal with a small file, 10# (or 8#) K-file, a radiograph was taken to determine the work length and confirm the canal morphology. After finishing root canal filling, another radiography was taken. The root canal configuration were assessed and classified on the basis of Fan`s and Melton`s category standard.
Results: According to radiographic characteristics and Fan`s classification, of 1146 mandibular second molars, 141 (12.30%)exhibited type I, 173(15.10%) and 135(11.78%) exhibited type II, III respectively. General C-shaped canal system incidence was 449(39.18%). Combined pulp floor and orifice configuration probed by clinical examination with radiography, of 1146 mandibular second molars, 473(41.27%) had C-shaped root canal system. Of teeth with the C-shaped root canal, 99(20.93%) presented category I, 291(61.52%) and 83(17.55%) presented type II, III respectively, assessed and classified as Melton`s category standard.
Conclusion: There was high incidence of C-shaped root canal system in mandibular second molar in Chinese. Existing of C-shaped root canal system with complex configure made the root canal therapy more difficult. Preoperative radiography, work length radipgraphy, postoperative radiography were required in determining the existing of C-shaped root canal system. Operative microscope facilitated the determination.