Beta Angle: A Cephalometric Analysis Performed in a Sample of Pakistan Population

OBJECTIVE

The purpose of this study is to evaluatethe reliability of a new cephalometric sagittal analysis i.e. Beta angle in Pakistani population and to compare its accuracy with angle ANB.Material and methods:One hundred and one pre-treatment cephalometric radiographs were traced and divided into 3 skeletal classes (class I, II, and III) based on angle ANB measurement. Betaangle was also traced and measured to obtain the values in all the skeletal classes and to compare with ANB angle to check the reliability.Results: The mean value of Beta angle for Class I skeletal pattern was (30.4°) ±2.6 SD, whilemean value for class II patients was (26.9°) ±6 SD. Beta angle for skeletal class III cases was (34.7°) ±5.4 SD. There was statistically significant negative correlation between ANB and Beta angle (r=0.59) while comparison of all skeletal classes also show significant difference between groups (p=0.00). Conclusion: Beta angle can be an alternate analysis to diagnose sagittal skeletal discrepancies with equal accuracy.

KEYWORDS

Beta angle, Cephalometric Analysis, ANB.

Introduction

Inorthodontic diagnosis and treatment planning of skeletal malocclusions, the evaluation of the antero-posterior (AP) jaw relationship is an indispensable step, and this relationship is usually determined by cephalometric analysis1. To evaluate this relationship, various measurements have been suggested for instance the ANB angle1 and the Wits1 appraisal. But such measurements can be effected by various factors and can often be misleading. For instance variation in position of nasion or rotation of the head sideward or upward during x rays exposure of lateral cephalogram, can affect the ANB reading. Furthermore, rotation of the jaws by either growth or orthodontic treatment can also change the ANB reading. The angle can also differ because of variance in the length of the cranial base2. Wits² appraisal was projected to overcome the existing limitations of angle ANB.Wits does not use nasion in its analysis,to reduce the misleading factors rather it uses the occlusal plane asa reference plane to describe the skeletal discrepancies. But the occlusal plane can be easily affected by tooth eruption and dental development as well as by orthodontic treatment^3-5. This can profoundly influence the Wits appraisal. Furthermore, accurate identification of the occlusal plane is not always easy or accurately reproducible^6,7, especially in mixed dentition patients or patients with open bite, canted occlusal plane, multiple impactions, missing teeth, skeletal asymmetries or steep curve of Spee. Cephalometric measurements, such as the ANB angle and the Wits appraisal, cannot be accurately used because of their dependence on varying factors8,therefore a recently developed angle named the Beta angle9 was introduced which does not depend on any cranial landmarks or dental occlusion.

The purpose of this article is to perform Beta angle analysis in a sample from Pakistani population and compare its reliability with angle ANB.

MATERIAL AND METHODS

A cross-sectional study was carried outin the department of Orthodontics at Baqai Dental Hospital, Karachi, using randomly selected lateral cephalograms of 101 patients. Sample comprised of 66 females and 35 male patients, ages ranged between 10 and 28 years. Duration of the study was 6 months. All classes of malocclusion were included in the study.The exclusion criteria for the study were patients having craniofacial anomalies and cleft palate or any history of previous orthodontic treatment.

The lateral cephalograms of all the patients were traced for angle ANBin the following manner:

ANB Angle: Following landmarks were used to measure the ANB angle: (Figure 1)
• S (Sellaturcica )
• A point(subspinale)
• B point (supramentale) Angle ANB was measured in the following way:
• SN line drawn fromsella to nasion
• NA line drawn from nasion to point A
• NB line drawn from nasion to point B

SNA is angle between SN line and NA line
SNB is angle between SN line and NB line
ANB angle was calculated which is the difference between the SNA and the SNB angle.
All the patients were divided into 3 skeletal classes based on angle ANB (i.e. Class I if ANB=2-4°, Class II if ANB >4° and ClassIII if ANB < 2°).
Beta angle was measured on all the cephalometric tracings in the following manner: Beta Angle: Following landmarks were used to measure the Beta angle: (Figure 2)
• A point (Subspinale)10
• B point (Supramentale)10
• C point (Thecenter of the condyle)
• Line connecting the center of the condyle C wth

B point (C-B line)
• Line connecting A and B points(A-B line)
• Line from point A perpendicular to the C-B line

Betaangle was measured between the perpendicular line (dropped from point A to the C-B line) and the A-B line.

All the data was recorded and analyzed through SPSS version 17.Pearson correlation was applied to evaluate the linear relationship between ANB and Beta angle while one way analysis of variance (ANOVA) was used to determine the difference between mean Beta angle values in all three skeletal classes.

Results

In this study the mean value for Beta angle in Class I skeletal pattern was 30.4°, with a standard deviation of 2.6°. The mean value for Beta angle in Class II skeletal pattern was 26.9° with a standard deviation of 6.0° while the mean value for Beta angle in class III skeletal pattern was 34.7° with a standard deviation of 5.4° (Table 1).

There was statistically significant negative correlation found between ANB and Beta angle (r=0.59) (Table 2)

To determie whether there was significant difference between means of Beta angle values of the three groups,ANOVAwas applied which showed significant difference between all three skeletal classes(p=0.00) (Table 3).

Discussion

An accurate antero-posterior measurement of jaw relationships is critically important in orthodontic treatment planning. Previously described angular and linear measurements (ANB angle and Wits appraisal) can beinaccurate because of their dependency on planes such as occlusal plane, SN plane and various factors such as patient’s age, jaw rotations, poor reproducibility of landmarks and growth changes in reference planes11. All these factors make the interpretation of these angles more complex than previously thought. The basic purpose of this study was to check the reliability of newly introduced cephalometric measurement, named the Beta angle, to assess the sagittal relationship between maxilla and mandible with accuracy

The sample size in this research comprised of 101 patients, in which 74 patients were Class I, 21 patients were class II and 6 patients were skeletally class III, based on angle ANB. In a similar research conducted by Baik and Ververidou9 in Greece on white population with a sample size of164 pre-treatment cephalometric radiographs; that consisted of Classes I, II, III cases,were 76, 42 and 46 respectively.In this study the value of Beta angle in Class I patients (ANB 2-4°)was found to be 25-35°. This finding was very close to a study conducted by Baik and Ververidou9in which they found the value of Beta angle in Class I patients to be 27-35° but they considered angle ANB as 1-3° for Class I patients. In Class II patients i.e. ANB > 4° the Beta angle was found more acute i.e. <25° in this study which is in correspondence with the study by Baik and Ververidou9 in which Beta angle was established to be<27° for class II patients. For- Class III patients (ANB < 2°) Beta angle was established to be > 35°in this research which is similar to the study conducted by Baik and Ververidou⁹

In this study the mean value for Beta angle in Class I skeletal pattern was 30.4°, with a standard deviation of 2.6 while according to Baikand Ververidou9, the mean value for Beta angle in class I skeletal pattern was (31.1°) ±2.0 SD.In anotherresearch by Doshi, Trivedi and Shyagali12 Beta angle was found to be 30.87° in Class I Indian population.The mean value for Beta angle in Class II skeletal pattern was 26.9° with a standard deviation of 6.0 while in another study9 the mean value was found to be (24.5) ±3.0 SD. The mean value for Beta angle in class III skeletal pattern was34.7° with a standard deviation of 5.4 while the mean value obtained in other study9 was (40.1)±4.2 SD. Pearson’s correlation between angles ANB and Beta angle showed a significant relation but negative i.e. an inverse relationship.That means if the value of ANB angle increase, Beta angle will decrease or vice versa. In anotherresearch by Erum and Fida12, a weak correlation between ANB and Beta angle was found. Another set of comparison was conducted between the mean values of Beta angle showing a significant difference among three skeletal classes. Similar result was also reported by Baik and Ververidou9 in their study.

Although Beta angle was found to be a reliable method to diagnose skeletal class with equal accuracy with ANB butit is difficult to locate the axis of the condyle due to artifacts in the cephalometric X-rays used. To overcome this drawback, digital radiographs should be used instead of conventional ones. Further studies should be carried out in future to check the reliability of the Beta angle and compare with other analyses for accurate diagnosis Furthermore Beta angle does not diagnose which jaw is involved in skeletal discrepancy whether maxilla or mandible, therefore other cephalometric analyses need to be used to assess the position of the jaws

Conclusion

1. The Beta angle is equally reliable method to diagnose skeletal sagittal malocclusion and can be used as an alternative to angle ANB as it correlated significantly with angle ANB.
2. Significant difference was found in the mean value of Beta angle among Class I, II and III malocclusion groups.

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