Abstract: PURPOSE: To observe root canal system of multi-canal mandibular first premolars and to analyze the morphology of them by micro-CT and three-dimensional reconstruction. METHODS: Thirty-two extracted mandibular first premolars with multiple root canals were selected and scanned by micro-CT. The number and morphology of canals, location of bifurcation and 5 subtle structures (lateral canals, apical ramification, isthmus, loops, apical delta) were analyzed. RESULTS: In the 32 specimens, 96.88% contained radicular depressions or grooves. The canal configuration was type Ⅱ, Ⅲ, Ⅴ: 3.12%, type Ⅳ: 31.25%, type Ⅷ: 9.38%, type Ⅸ: 15.62% and C-shaped canal: 34.38% by Vertucci's classification. 62.50% of the canals bifurcated at the middle third of roots, comparing with 37.50% at apical third. The incidence of the lateral canals, apical ramification, isthmus, loops and apical delta was 56.25%, 43.75%, 40.62%, 21.88% and 6.25%, respectively, which were all found at the middle and apical third of roots except that lateral canals were found at all depth of canals. CONCLUSIONS: Most mandibular first premolars with multiple canals contain radicular depression or grooves, of which root canal system are complicated. Micro-CT can provide clear and accurate three-dimensional information of canal morphology.

Key words: Mandibular first premolar, Root canal morphology, Micro-CT