RÉSUMÉ
A thorough knowledge of root canal anatomy and an understanding of its potential anatomic variations are essential for a successful root canal therapy. The most probable reason for failure is the inability to recognize the numerous variations in canal morphology. Mandibular premolars due to such anatomic variations, are considered the most difficult teeth for root canal therapy. If the entire root canal system is not properly located and treated, failure and flare- ups would follow. The purpose of this study was to evaluate the incidence of multiple roots and canals radiographically in mandibular premolars among an Iranian population referred to dental faculty of Shiraz University. One thousand and one hunrdeel [1100] full mouth series [FMS] radiographs of patients undergoing periodontal treatment were randomly selected. From among these radiographs, those full mouth series with four mandibular premolars free of any kind of root canal therapy, were included in the present study. Consequently, 1052 FMS were evaluated. From 2104 mandibular first premolars, 15% had more than one canal and 1.5% had more than one root. Among mandibular second premolars, 77 teeth [3.65%] had more than one canal where as 9 teeth had more than on root. There were 107 cases with more than one canal bilaterally, from among them in 8 cases all four mandibular premolars had more than one canal, in 12 cases three mandibular premolars had multiple canals bilaterally and in [87] remaining cases only two. mandibular premolars had bilaterally multiple canals. In nine cases of mandibular premolars. Multiple canals were observed bilaterally. The results of this study suggest that the probable incidence of multiple canals among mandibular first premolars is greater than mandibular second premolars. The frequency a multiple roots and canals in mandibular premolars are not affected by sex type. Since conventional radiographs in the department of periodontics are taken at a vertical angle to the teeth buccal surface, the probability of hiding multiple canals is high. Therefore, the mentioned results should be considered as the minimum probable cases for multiple roots among the teeth under investigation