Objective To compare the consistency of root canal configuration types of mandibular first premolar by using micro-CT and radio visio graphy（RVG）. Methods One hundred extracted mandibular first premolars with complete dental root and apex which received no endodontic treatment were randomly selected. Each tooth was radiographed with RVG through a buccolingual and mesiodistal direction, and then scanned with micro-CT and reconstructed. The classifications of the root canal types according to Vertucci’s type with the two methods were compared. Results The canal patterns were classified as type Ⅰ（67%）, type Ⅲ（3%）, type Ⅴ（18%）, type Ⅶ（2%）, additional type（10%） with micro-CT and canal patterns as type Ⅰ（71%）, type Ⅲ（2%）, type Ⅴ（23%）, type Ⅶ（1%）, additional type（3%） with RVG. 63% of teeth showed one canal in both micro-CT and RVG. Only 25% of teeth were diagnosed as complex canal by the same canal type in both micro-CT and RVG. The Kappa value between micro-CT and RVG was 0.541 which suggested that the two kinds of methods had intermediate consistency. 82.8% of the premolars with root groove had two or more than two canals. Conclusion Although RVG can basically reflect the root canal system type of the mandibular first premolars in vitro, it offers poor accuracy images to complex root canals. Micro-CT threedimensional images could clearly and precisely display the root canal system morphology of the mandibular first premolars in vitro.
