Aim To evaluate the spiral CT manifestations and its diagnostic efficacy in the aortic dissection. Methods Twenty-three patients underwent 25 spiral CT examinations totally. The spiral CT features were classified into specific and non- specific spectrums for analysis. Results Specific signs emerged as true and false double aortic lumen in 22 cases (95.7%),the intimal flap 22 (95.7%). Non-specific signs include irregular aortic dilatation in 23 cases all (100%),thickening and calcification of the aortic wall 21(91.3%),intraluminal thrombus 4 (17.4%). The diagnostic accuracy of spiral-CT achived 95.7%. Conclusion Spiral CT is a valuable tool in the assessment and diagnosis of aortic dissections. were from eighteen to twenty five years old without orthodontic history Chengdu were randomly collected in. All teeth must be free of visible malform, aberration, and fully erupted. Impressions were taken, and measurements were made, parallel to the occlusal plane at the greatest mesiodistal width of each tooth on dental cast with electronic caliper (0 01 mm). Each tooth was measured twice and the average of the two readings was taken as the dimension for that individual tooth. Mesiodistal crown diameters were statistically analyzed with t test and linear regression, using the SAS (Statistic Analyses System) computer package. Results: It was found that mesiodistal crown diameters had significantly statistical difference in gender. Hence the mesiodistal crown diameters were assessed and investigated separately for the male and the female. It was also found that the total mesiodistal crown diameter of lower incisors was closely correlated with the total mesiodistal crown diameter of canines and premolars. The correlation coefficients between the independent variable and dependent variables were 0 599 for upper canines and premolars and 0 654 for lower canines and premolars in the males and 0 586 and 0 635, respectively, in the females. The P were found to be less than 0 001 for both arches. The correlation coefficients had significantly statistical difference. Conclusion: The equations predicting overall mesiodistal crown diameters of upper and lower unerupted canines and premolars for male and female Chinese people were established respectively: Maxillary (y=10 87+0 51 x (male)), y=11 88+0 46 x(female), Mandibular (y=10 36+0 50 x(male), y=10 03+0 49 x(female)), y(total mesiodistal crown diameter of canines and premolars), and x(total mesiodistal crown diameter of lower incisors).\;Key words:\ mesiodistal diameter\ \ space analyses\ \ linear regression\ \ predicting equation