Evaluation of Skeletal Jaw Relation by Different Cephalometric Angles for Sample of Kurdish Young Adults in Sulaimani City-A Cephalometric Study

An accurate evaluation of skeletal sagittal jaw relationship has an important role in orthodontic diagnosis and treatment planning. This study was done to establish cephalometric norms of all types of malocclusion using ANB, Wits appraisal and Beta angle, and evaluate the signicance of W angle in comparison to these parameters. Ninety pre-treatment lateral cephalograms of male and female patients aged 18-28 years from Sulaimani City that met the sample criteria were traced digitally by the Easy Dent 4 software program. The sample was divided into three groups of skeletal malocclusion, class I, II, and III, based on ANB angle, Beta angle, and Wits appraisal, each group consisting of 30 patients. For each subject the following cephalometric parameters were measured: ANB angle, Beta angle, Wits apprasial, and W angle.


Background
In the eld of orthodontics, discrepancies of the jaws can be described in three planes, namely transverse, sagittal and vertical (1). Of these, the sagittal discrepancies are of most concern to the patient. Hence, in orthodontic diagnosis and treatment planning, an accurate measurement of sagittal discrepancy is critical (2). However, the evaluation of the sagittal relationship of maxilla and mandible has posed a major problem. The causes of this problem are the change in the sagittal relationship due to rotations of the jaws during growth, and a lack of validity of the various methods proposed for their evaluation (3).
The importance of the sagittal jaw relationship for patients and orthodontists has led to introduction of many linear and angular cephalometric parameters for its measurement, including ANB angle, Wits appraisal, and Beta angle (4). But they all have shortcomings and drawbacks (5).
To overcome these problems, in 2013, Bhad et al. (6) introduced the W-angle. This is the angle between the perpendicular line from point M to the S-G line and the M-G line (Fig. 1). The use of this angle has many advantages. Firstly, it has not dependent on unstable landmarks or dental occlusion. Therefore, it is a valuable tool for assessing true sagittal changes because of growth and orthodontic treatment (6).
Secondly, in skeletal patterns with clockwise or counterclockwise rotation of the jaws as well as during transitional periods when vertical facial growth is taking place, W angle is a useful sagittal parameter (7).
Finally, it can be used for treatment planning during orthopedic or orthognathic procedures as this angle is independent of the cranial base length (position of point N) that sometimes camou ages the true skeletal class I, II and III patterns (8).
Moreover, cephalometric analysis is practiced by comparing the patient's radiographic measurements with norms or standard values, most of which are obtained from samples of European or American populations. Therefore, the application of these norms in other populations may give error because of possible ethnic and racial variations (7).
The aim of this study is to evaluate the signi cance of W angle in the diagnosis of the antero-posterior jaw relationship in comparison to other skeletal sagittal dysplasia indicators, including ANB angle, Beta angle and Wits appraisal, in class I, class II, and class III types of malocclusion. And to establish cephalometric norms of all types of skeletal sagittal malocclusion using ANB, Wits appraisal, and Beta angle for a sample of Kurdish young adults in Sulaimani City.

Subjects And Methods
The sample consisted of 124 cephalograms of the total 311 patients examined clinically (male and female) with class I, class II, or class III malocclusion. Ninety patients tted the criteria of the study, while 34 cases were excluded due to poor quality of cephalometric radiograph or failure to communicate with the patients. Among the selected cases 40% were male (36 cases) and 60 % were female (54 cases).
These 90 cases were randomly divided into three groups, based on class I, II, III classi cation, with 30 cases in each group (Fig. 2).
The present study was conducted in patients who were seeking orthodontic treatment in the Orthodontic department of Shorsh teaching dental center in Sulaimani City. Ethical committee approval was obtained before starting the study (Appendix I).
Criteria For Selecting The Cases 1-Patients originating from Sulaimani Governorate, as ethnically veri ed by patient histories (all three grandparents of both parents were Kurdish and from Sulaimaniyah Governorate).

2-Patients aged between 18 and 28 years old.
3-Patients with complete permanent dentition including second molars. When the patient came to the dental center seeking orthodontic treatment, informed consent was not taken for exposure to a lateral cephalogram, because a lateral cephalogram and orthopantogram is required as part of the routine diagnosis procedure.
Two nger method by Foster was used for the initial classi cation of the sagittal skeletal malocclusion (9). Then the researcher lled in the data recording sheet for each case (appendix II). After that, the patients were referred for a lateral cephalometric radiograph (ceph). All the cephs were taking by one radiologist. These cephs were obtained using the cephalogram [pax-i3D system (Pano-Cephalo-CT), 2014]. The machine was set at 84 kilovoltage peak (kVp), 10.0 milliampere (mA) and exposure time of 1.2 seconds (s). Cephs were taken with teeth in centric occlusion, lips in relaxed posture and the head in the natural head position with the Frankfort plane parallel to the oor (10).
Cephalometric landmarks and planes used in this study for analyses (3,6) S The midpoint of the pituitary fossa (sella turcica).

M
The midpoint of the premaxilla, identi ed as the mid-point of the largest circle that could be drawn in the premaxilla tangent to the anterior and superior walls of the premaxilla.  After measuring the following variables: ANB, Beta angle and Wits appraisal, separately for each patient as shown in (Fig. 3A,B,C), the patients were classi ed into class I, II or III skeletal pattern groups, two of the three parameters were required to meet the same criteria and be within the same class (6). Table 1 shows the distribution of the patients who ful lled the criteria across the class I, II, and III study groups. Table 1 The criteria that included in the classes I, II, or III skeletal pattern for grouping of study Skeletal class ANB angle (11) Wits appraisal (12) Beta angle (13) Class  2012)). This software program had options for adjustment of the radiograph by adjusting the contrast and brightness to facilitate the identi cation of the landmarks, in addition to zoom option and magni cation for better viewing and differentiation of the landmarks. All the tracings were performed by the principal investigator (Mohammed sh).
After sample classi cation, W angle was constructed and measured (Fig. 4). According to Bhad et al. (6), W angle between 51-56 ° is considered as class I skeletal pattern, while an angle less than 51 ° is considered as skeletal class II relationship, and an angle greater than 56 ° is considered as skeletal class III (6).
To assess the reliability and reproducibility of the Ceph analysis, ve parameters/variables from 10 randomly selected cephalograms were traced twice at a two-weeks interval by the same observer and were then tested by the paired t-test, with the mean differences in the measurements found to be nonsigni cant. The inter-examiner reliability was assessed in the same way as for the examiners' measurement and then tested using one way analysis of variance (ANOVA). No differences were found in the results.

Statistical analysis
The Statistical Package for Social Sciences (SPSS, version 22) was used for analyzing data. The Shapiro Wilk test was done to test the normality of the data. According to the P-values, the data were normally distributed. Hence, parametric tests such as ANOVA were used to compare the means of the three study groups. The post-hoc test was used to compare each two groups, Pearson correlation coe cient (r) was used to assess the strength of correlation between two numerical variables, and coe cient of variability was used to measure the extent of variability of the variable in relation to the population. The signi cance alpha level was set at p value of ≤ 0.05. Table 2 shows the descriptive statistics for the mean, standard deviation, coe cient of variability, minimum and maximum for Beta angle, ANB angle, Wits appraisal and W angle.  Table 3 shows the differences found in the means of Beta angle, ANB, Wits appraisal and W angle readings between and within the three classes, which were all signi cant (p < 0.001).  Table 3 shows that in class I patients, all of the correlations between the studied parameters were weak and not signi cant (r < 0.4, and P > 0.05), except for the correlation between W angle and Wits appraisal, which was a signi cant positive correlation (r = 0.382, p = 0.037). In class II patients, all the correlations were weak and not signi cant, except for a negative, moderate strength signi cant correlation between W angle and ANB angle (r = -0.563, p = 0.001).

Results
The picture is different regarding class III patients. Strong inverse signi cant correlation was detected between Beta angle and ANB angle (r = -0.725, p < 0.001). The same was found for the correlation between Beta angle and Wits appraisal (r = -0.820, p < 0.001). A nearly strong positive signi cant correlation was detected between the Beta angle readings and W angle readings (r = 0.686, p < 0.001). Strong signi cant positive correlation was detected between ANB angle and Wits appraisal (r = 0.719, p < 0.001). There was a negative strong signi cant correlation between ANB angle readings and W angle readings (r = -0.723, p < 0.001). Finally, an inverse, nearly strong, signi cant correlation was observed between Wits appraisal and W angle (r = -0.678, p < 0.001).

Discussion
Evaluation of the antero-posterior jaw relationship is an obligatory step in orthodontic diagnosis and treatment planning and this procedure is essentially done by cephalometric analysis (8).
Both angular and linear variables are utilized cephalometrically to analyze the skeletal sagittal jaw relationship. A search of the literature indicated that various parameters are available to assess the sagittal relationship but none of them can be applied with maximum reliability (14).
Therefore, this study aimed to analyze different geometrical and statistical variations in cephalometric parameters which were used to indicate the antero-posterior jaw relationship in class I, class II and class III malocclusions and to compare the accuracy of the recently proposed W angle with these parameters for measuring antero-posterior jaw discrepancies in a sample of the Kurdish population in Sulaimani City.
All sagittal jaw analysis parameters invented over the years are affected by at least one of the following factors: jaw rotations, poor reproducibility of landmarks, patient's age changes during orthodontic treatment and growth changes in reference planes (15). Therefore, to overcome the limitations of the other parameters the W angle was produced.
The ANB angle was developed by Riedel in 1952(11). Until now it is considered the most popular and widely used angle for assessing the sagittal jaw relationship. However, it is affected by jaw rotation due to orthodontic treatment or growth. In addition, any displacement in point N has an in uence on ANB values (11). When using the ANB angle many factors, including the length of the anterior cranial base, growth rotation of the jaws, vertical growth and patient age, should be considered, which makes the assessing of this angle much more complicated (16). In the present study, the mean values of this angle were near to those of Riedel's standards and the results of our study showed that the ANB angle values are signi cant among the groups. However, it is affected by various factors which can often lead to error.
To overcome the controversies surrounding the ANB angle, the Wits appraisal was introduced by Jacobson in 1975 (17). Although landmarks identi cation or jaw rotations have no effect on it, its accuracy is affected by the need to correctly identify the functional occlusal plane, which can sometimes be impossible, especially in patients with open bite, in mixed dentition, multiple impactions, missing teeth, severe cant of the occlusal plane, and skeletal asymmetries, or steep curve of Spee (18). Additionally, the functional occlusal plane may be changed by orthodontic treatment, which can in uence the Wits measurement. Therefore, in these cases the Wits appraisal will not re ect pure sagittal changes of the jaws (3). The mean values of the present study were near to those of Jacobson, the results showing signi cant differences in all three groups. However, the location of the functional occlusal plane itself was di cult, as con rmed by Moore et al. and Ishikawa et al. (19,15).
The present study showed that the Beta angle values were statistically signi cant among all groups, as supported by Biak and Ververidou, who stated that the Beta angle remains relatively stable even when the jaws are rotated, and it does not depend on the functional occlusal plane or cranial landmarks (13). When there is clockwise or counterclockwise rotation of the jaws, the Beta angle can assess the sagittal jaw relationship more accurately. Nonetheless, it still uses point A and point B which are considered to be affected by alveolar bone remodeling associated with growth or orthodontic movement of the incisor teeth (20).
To overcome some of the above limitations of other parameters, a measurement was developed that was named the W angle. This angle does not depend on any unstable landmarks or dental occlusion and therefore would be especially valuable to assess true sagittal changes due to growth and orthodontic treatment. In the present study the mean values of W angle were near to those found in the Bhad et al. (6) and Al Mashhadany (21) studies. The present study disagrees with Mittal et al. study (5), although this might be due to difference in sample size or ethnic differences. The present study shows that W angle values were statistically highly signi cant among the groups. This agrees with Bhad et al. study which proposed that this angle is an indicator for sagittal skeletal dysplasia (6). As W angle uses three stable landmarks: point S, point M, and point G, the W angle remains relatively stable even when the jaws are rotated or growing vertically. This is because of rotation of the S-G line along with jaw rotation, which carries the perpendicular from point M with it (6).
Another advantage of W angle is that it can be a valuable tool for planning orthopedic or orthognathic procedures as this angle is independent of cranial base length which will be affected by the position of point N and can sometimes camou age true skeletal class I, II, and III patterns (3). The present study results showed that the coe cient of variability was highest for Wits appraisal and lowest for W angle in all three classes, agreeing with Mittal et al. (4) and Sharmaet al., (7) studies. This indicates that Wits appraisal is a highly variable parameter and W angle is the least variable and most homogeneously distributed parameter in intra-group comparisons.

Correlation of the study parameters in class I patients
The present study showed that in class I group, all of the correlations between the studied parameters were weak and not signi cant, except for the correlation between W angle and Wits appraisal, where there was signi cant positive correlation. The ndings agree with Mittal et al. (5) study, but disagree with Sharmaet al., (7) study which found that in class I subjects ANB angle correlated positively with Wits appraisal. Additionally, our study disagrees with Pervez and Ahmed (8) and Al-Mashhadany (21) studies which reported strong negative correlation between W angle and ANB angle in CL I malocclusion.

Correlation of the study parameters in class II patients
The present study showed that in class II group, there was a negative, moderate strength signi cant correlation between W angle and ANB angle, which agrees with Sharma et al. (7) and Pervez  Correlation of the study parameters in class III patients The ndings of this study showed a strong negative signi cant correlation between ANB angle and Beta angle, and a strong signi cant positive correlation between ANB angle and Wits appraisal. These results agree with Mittal et al. (5) study. In CL III group, the W angle showed strong positive signi cant correlation with the Beta angle, and signi cant correlation with Wits appraisal. Moreover, there was a negative strong signi cant correlation between the ANB angle readings and the W angle readings. These results agree with the ndings by Pervez and Ahmed (8), and AL Mashhadany (21). However, they disagree with the Mittal et al. (5) results which showed only a negative correlation between W angle and ANB angle and no signi cant correlation between other parameters.
The Beta angle is similar to W angle in being unable to determine which jaw is prognathic or retrognathic in class II and class III skeletal cases. To clarify this, clinicians should be aware of the importance of other cephalometric measurements (8). The relatively new W angle is evidently the most stable and reliable angle for measuring skeletal sagittal discrepancies (22).

Conclusions
Among the study sample of Kurdish young adults in Sulaimani City, the mean respective values of ANB angle for class I, II, and III malocclusion were 2.74 °, 5.85 ° and − 3.29 °, for B angle they were 32.39°, 25.23° and 42.96°, while for W angle they were 54.1°, 48.34° and 60.07°. The ANB angle, Beta angle, Wits apprasial and W-angle are signi cant parameters for assessing the sagittal jaw relationship between maxilla and mandible; however, to overcome the limitations of each at least 2-3 parameters should be used.
Declarations Figure 1 The construction and mode of measuring the W angle (3) Page 15/16 Wangle identi cation

Supplementary Files
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