The conformity of Y axis angle with the texts and Bolton values in 15- 30 years old individuals (1995-99)

Y axis angle is one of the measurements which is used in assessment of mandibular growth pattern. It seems, is not in coordination with the mentioned 66 degrees in texts and is more in our patients. Thus in this study, Y axis angle is measured in lateral cephalograms of over 15 year old Iranians, to find if there is any difference. Methods & Materials: In this descriptive study, two hundred conventional lateral cephalograms were traced. Y axis angle and another angles showing vertical growth of mandible were measured. The cephalograms were divided in to three groups of horizontal and three groups of vertical growth. The difference between each three groups were assessed by ANOVA. The correlation between vertical angles was assessed by Pearson analysis. The mean of Y axis angle in 17-18, 19-20, 21-30 years old was compared with Bolton measurements by t-test. Y axis was 68.83±5.34 in boys and 68.67±4.8 in girls. The difference was not statistically different. The difference between the vertical groups was significant (P<0.01). The difference between Cl III and Cl II, Cl III and Cl II was significant (P<0.05). The correlation was strong between Y axis and GoGn/SN and sum of posterior angles (r=0.76) and moderate between Y axis and MPA angles (r=0.56). The most significant difference was seen in 17-18 year old girls (64.6±4) in comparison with Bolton study (67.2±3) (P<0.05). Bolton measurements can be used for other compared ages in both sexes. It is recommended to use standard deviation for 66 of Y axis, thus we would be able to apply it to larger populations.Keywords: