Abstract: Objective: To investigate the anatomical morphology of root and root canal system of deciduous molars in Shanghai area by using cone-beam computer tomography (CBCT), for better clinical diagnosis. Methods: CBCT images of 167 cases (age from 4 to 7) were selected randomly. To measure the number of roots, teeth-length and to analysis canal configurations statistically. Results:①Three roots accounted for 50.30% and double roots were 47.59% in maxillary first deciduous molar. Three roots of maxillary second deciduous molars were highest (99.37%). The mandibular first and second deciduous molar roots were double roots (91.48%、72.95%). ②Palatal root teeth-length of maxillary primary molars was higher than that of buccal roots. There was no significant difference between mesial and distal root tooth length in mandibular first deciduous molars and the mesial root tooth length was longer than that of distal root in mandibular second deciduous molars. ③The number of root canals in maxillary first deciduous molar were mostly three canals (97.59%). The incidence rate of three and four canals, in maxillary deciduous second molars, were 87.13% and 12.27%. The canal curvature of maxillary deciduous molars had type I, type II, type III and type IV, with type I being the majority. ④ In mandibular first deciduous molars, 41.96% of the cases were found to have three canals, of which 39.10% have two canals in mesial canal and 60.90% have two canals in distal canal, four canals were 39.75%, and double canals were 18.30%. The majority of mandibular second deciduous molars were four canals (83.28%). The canal types in mandibular deciduous molars were mainly type I and type IV. Conclusion: The anatomical structure of canal system is of diversity and complication in deciduous molars. The canal structure variation rate of maxillary second and mandibular first deciduous molars were higher than that of else deciduous molars, with CBCT good for diagnosis.

Key words: Deciduous molars, CBCT, Teeth-length, Root canal type