Objective To study the root canal curvatures of adolescents’maxillary first premolars in Guangdong province and the differences between male and female were studied. Methods 200 maxillary first premolars among adolescents in Guangdong Province（100 males and 100 females） were numbered in proper. After access preparation, a K-file was inserted into the canal until the tip of the file was just seen at the apical foramen. Then standardized periapical images were taken from mesial-distal and buccal-lingual directions with radio visio graphy. The angle of canal curvature（CCA） was determined according to the method described by Schneider. Then the curved canals whose angle were more than 5° were chosen, and the canal access angle（CAA）, curvature height（X） and curvature distance（Y） were determined according to the method described by Günday. Linear correlations of the measurements were analyzed. Results 59.21% of the total roots were curved in buccal-lingual directions. The incidence rates of males’and females’were 49.74% and 68.98%, respectively. 41.05% of the total roots were curved in mesial-distal directions. The incidence rates of males’and females’were 36.27% and 45.99%, respectively. 6.84% of the total roots were S-shaped curves. 4.15% and 9.63% of canals from male and female were S-shaped curves, respectively. The curvatures of single root canals between male and female had statistical differences in buccal-lingual directions （P＜0.05）. The curvatures of the lingual root canals from females in buccal-lingual directions and mesial-distal directions was higher than males’（P＜0.05）. The Y of buccal root canals in buccal-lingual directions and mesial-distal directions and the CCA of lingual root canals in buccal-lingual directions between male and female had statistical differences（P＜0.05）. The CAA of curved buccal canals and curved palatal canals from female and female had positive correlation with CCA and X（P＜0.01）, while negative correlation with Y（P＜0.05）. Conclusion There are curved root canals in buccal-lingual and mesial-distal directions in the maxillary first premolars, and some curved root canals were S-shaped. The curved canals incidence rate of females was higher than males.
