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Comparison of ANB Angle, Yen Angle and W Angle in Chinese Population

Introduction: An accurate, reliable and stable method of accessing sagittal jaw relationship with cephalometric analysis is essential in orthodontic diagnosis and treatment planning. Many methods have been developed to assess antero-posterior jaw discrepancy but they all have some shortcomings including ANB angle. Thus the purpose of this study is 1) To provide mean values and standard deviations for ANB angle, Yen angle and W angle for a sample of skeletal Class I, II and III Chinese males and females malocclusion patients; 2) To verify the existence of sexual dimorphism; 3) To compare these three methods for assessing sagittal jaw relationship 4) To assess the correlation between these and 5) To find out which is the most reliable amongst them. Materials & Method: 120 pretreatment lateral cephalograms of Chinese patients, including both males and females between 18 to 25years old, were collected from the Department of Orthodontics; Wuhan Union Hospital which were divided into 3 groups as Class I, II and III skeletal pattern. Each pattern consists of 40 samples. The values of the males and females were compared with independent t-test while the inter-group comparisons were conducted with ANOVA and Tukey’s test. Pearson correlation test was performed to correlate between these angles. Result: There were no statistically significant differences between the mean values of these angles in male and female within the groups in all three classes. ANOVA analysis showed significant differences were found in ANB angle, Yen angle and W-angle in all the three Groups. Strong correlation existed between Yen angle and W angle. Conclusion: There is no existence of sexual dimorphism in our study. ANB angle is affected by growth of Nasion while Yen angle is affected by rotation of jaws. ANB angle is easy to assess while W angle is most stable and reliable.


INTRODUCTION
In orthodontics, the cephalometer was introduced in 1931 by Broadbent in USA 1 and Hofrath in Germany 2 independently. Initially it was developed as a device to study craniofacial growth and development. Later it was also used for growth prediction, diagnosis and treatment planning and assessment of treatment progress of the patient.
During diagnosis and treatment planning of skeletal malocclusions, proper evaluation of sagittal jaw relationship is an important step which is generally determined by cephalometric analysis. Since Wylie's (1947) 3 first attempt to describe AP jaw relationship, many other cephalometric parameters have been proposed. Downs (1948) 4  Steiner's analyses. 6 Any cephalometric analysis based on either angular or linear measurements has obvious shortcomings and limitations, which have been discussed in detail by Moyers et al 7 and by Appasaheb Naragond et al. 8 Although the ANB angle is still very popular, useful and easy to analyze, some authors have shown that point A and B are influenced by growth and dentoalveolar remodeling during orthodontic treatment. Also the position of nasion is not fixed during growth, and any displacement of nasion will directly affect the ANB angle. There is often a difference between the interpretation of this angle and the actual discrepancy between the apical bases. 9 It is also noted that rotation of the jaws by either growth or orthodontic treatment

MATERIALS AND METHOD
For our study, the pretreatment lateral cephalograms of Chinese patients, including both males and females, were collected from the Department of Orthodontics; Wuhan Union Hospital affiliated to Huazhong University of Science and Technology. Only the radiographs with acceptable radiographic quality and minimal radiographic distortion were considered for the study. The following inclusion criteria was taken: 1. For the Class I skeletal pattern group-ANB angle of 1° to 3°, Wits appraisal between 0 and -3 mm and Pleasant profile.
2. For the Class II skeletal pattern group-ANB angle was above 4°, Wits appraisal greater than or equal to -1 mm and the profile had a Class II appearance.
3. For the Class III skeletal pattern group-ANB angle was less than or equal to 1°, Wits appraisal less than or equal to -4 mm and the profile had a Class III appearance.
The mean, standard deviation and P value were calculated for each parameter.
Comparison between both genders is done by using

RESULT
Independent t tests showed that there were no statistically significant differences between the mean values of these angles of male and female sexes within the groups since p value is greater than 0.05.
Therefore, all measurements belonging to both sexes were combined in each group and were considered for analysis.  Table 3 shows the correlation between these angles using Pearson's correlation coefficient. It shows that significant correlation between Yen angle and W angle in all three classes.  Since its introduction in 1952, ANB angle is still widely used and popular but many authors have shown that the point N is not fixed and any displacement will directly affect the ANB angle. 14   The main advantage of Yen angle is that it eliminates the difficulty in locating points A and B, or the