From Volume 7, Issue 4, October 2014 | Pages 137-139
The aim of this article is to derive an angle using panoramic radiographs which is as reliable as lateral cephalometric norms in determining the skeletal growth pattern. The sample size consisted of 60 OPGs of patients with normodivergent growth pattern evaluated from cephalometric radiographs. The mean Symphyseal Angle (SA) obtained was 134.1 ± 2.1 and correlation tests showed high, negative and statistically significant correlation for both Basal Plane Angle (BPA)
Panoramic radiography was first introduced by Yrjo Paatero of the University of Helsinki in 1961 and demonstrated the right and left anatomic landmarks for bilateral structures in a panoramic view.3 Orthodontic practice utilizes panoramic radiography for information on the teeth, their axial inclinations, maturation periods and surrounding tissues and is considered to be an indispensable orthodontic screening tool.4,5,6 Facial and mandibular asymmetries, bilateral condylar symmetry, bone trabecular pattern and alveolar support to the teeth are of major concern to orthodontists. Similarly, the growth pattern or the divergence of the jaw bases has to be determined in a patient to help decide on the type of mechanics to be employed.
The gonial angle measured from the lateral cephalogram is one of the most common methods of determining jaw divergence. However, the gonial angle has to be validated with other parameters because of its poor reliability as it measures the arithmetic mean of right and left angles.7 Recent studies have concluded that panoramic radiographs can also be used to determine the gonial angle as accurately as lateral cephalograms.8,9
One of the first attempts to determine skeletal pattern using panoramic radiographs was undertaken by Levandoski10 and since then very few studies have demonstrated the use of panoramic radiographs to determine growth pattern. The aim of the present study is to determine a more reliable angle that could be used as an adjunct to lateral cephalometric measurements to determine the growth pattern of the individual using panoramic radiographs.
Sixty panoramic radiographs (33 females and 27 males, age range of 14–25 years) were obtained from patients undergoing orthodontic treatment in the SDM College of Dental Sciences, Karnataka, India. All the patients had a normodivergent growth pattern which was determined using the lateral cephalograms from the following cephalometric criteria: Frankfurt Mandibular Plane Angle (FMA) of 25 ± 2°, Jarabak Ratio (JR)2 of 62–65%, and Basal Plane Angle (BPA)1 of 25 ± 2° (Figure 1). Panoramic and lateral cephalometric radiographs were obtained using a KODAK 9000 machine with the patients in the Natural Head Position. Radiographs of patients with asymmetry, bone disorders, cyst and tumours were excluded from the study and good quality OPGs with recognizable landmarks were used.
The radiographs were traced on a sheet of cellulose acetate paper using a 0.3 mm Staedtler Mars micro pencil. Landmarks on the panoramic radiographs were identified and marked. The use of a bite plate while taking the radiograph altered the relationship between the maxilla and mandible, leading to errors in the measurements obtained involving both the jaws. Therefore, independent reference planes were drawn on the mandibular panoramic images to ensure reliability of the measurements even with the use of a bite plate. A new angle called the Symphyseal Angle (SA) was defined and constructed based on these reference angles.
The SA was constructed from two tangents drawn at the most prominent point on the inferior border of the mandible in the canine and premolar regions, meeting at the midsagittal plane, drawn passing through the anterior nasal spine and between the two central incisors (Figure 2). To derive the midsagittal plane, a grid of 1 cm square was constructed and placed on the radiograph. All the radiographs were traced in this way and the SA was measured. To reduce the intra-operator errors, all the measurements were repeated after one week.
All the parameters were measured by the same examiner and repeated after one week. Hence repeatability coefficients were calculated for the initial and final measurements to eliminate intra-observer error. The mean values and the standard deviation of the parameters were calculated for both panoramic radiographs and lateral cephalograms. The correlations between the mean values of the panoramic measurement and their cephalometric correspondents were obtained. Regression equations were set for the significant correlations. Thus it was possible to calculate the significance level and the predictability of the information from the panoramic radiographs.
The repeatability coefficients were above 0.99 for all the parameters measured, confirming the reliability of the measurements. The mean Symphyseal Angle obtained from panoramic radiographs was 134.1° with a standard deviation of 2.11° (Table 1).
| Standard | Confid | Confid | ||||||
|---|---|---|---|---|---|---|---|---|
| Parameters | Mean | SD | Error | Median | -95.000% | +95.000% | Minimum | Maximum |
| SA | 134.38 | 2.11 | 0.46 | 135.00 | 133.42 | 135.34 | 131.00 | 138.00 |
| FMA | 25.40 | 1.14 | 0.25 | 25.00 | 24.89 | 25.92 | 23.00 | 27.00 |
| JR | 63.30 | 1.23 | 0.27 | 63.40 | 62.74 | 63.85 | 61.00 | 65.50 |
| BPA | 24.90 | 1.23 | 0.27 | 25.00 | 24.34 | 25.47 | 23.00 | 27.00 |
Key: SA – Symphyseal Angle; FMA – Frankfurt Mandibular Plane Angle; JR – Jarabak Ratio; BPA – Basal Plane Angle.
To summarize the results shown in Table 2:
| LC parameters | r-value | R2 | t-value | P-value | Reg equation |
|---|---|---|---|---|---|
| FMA | -0.4103 | 0.1684 | -2.8813 | 0.0063 | SA = 150.33-0.63 |
| JR | 0.3255 | 0.1060 | 2.2046 | 0.0332 | SA = 102.50+50 JR |
| BPA | -0.3066 | 0.0940 | -2.062 | 0.0456 | SA = 146.37-48 BPA |
Key: LC parameters – Lateral cephalometric parameters, p < 0.05; SA – Symphyseal Angle; FMA – Frankfurt Mandibular Plane Angle; JR – Jarabak Ratio; BPA – Basal Plane Angle.
Hence there was a significant correlation between the Symphyseal Angle and all the three parameters.
Panoramic radiographs have been used extensively to determine presence or absence of teeth, their root positions, bone architecture, relevant pathology and to determine the teeth eruption status. Recent studies have suggested that panoramic radiographs can be used as an adjunct to determine the growth pattern along with lateral cephalometric radiographs. These articles focus on measurement of the gonial angle since there is a possibility of error in the measurement of this angle using lateral cephalometric radiographs. Larheim and Svanaes stated that both panoramic radiographs and lateral cephalograms were accurate in determining the gonial angle and found no significant difference between the right and left sides in panoramic radiography.8
Fisher-Brandies et al indicated that the gonial angle obtained by panoramic radiography was 2.2–3.6° less than that obtained from a lateral cephalogram.11 Türp et al stated that vertical linear measurements on the condyle and the ramus are not reliable for patients with macerated skulls.12 On the contrary, Larheim and Svanaes emphasized that horizontal measurements obtained from OPG were unreliable. Therefore, only angular measurements were made on the panoramic radiographs.8 The horizontal distances are particularly unreliable as a result of the non-linear variation in the magnification at different object depths, whereas vertical distances are relatively reliable.13,14,15 However, other authors have found that the reproducibility of vertical and angular measurements is acceptable provided that the patient's head is correctly positioned in the equipment.16 Since there is a disparity in the reliability of gonial angle measurements obtained from a panoramic radiograph, an alternative to the gonial angle was determined.
This study was devised to derive an angle which is reliable and accurate in determining the growth pattern of an individual using panoramic radiographs. In order to derive an angle, a study population with normodivergent growth pattern (FMA of 25 ± 2, JR2 of 62–65%, BPA1 of 25 ± 2,) was selected. This would enable a check to be made for any deviation from the norms for hypo/hyperdivergent growth patterns. The pantomographs were taken in the Natural Head Position in order to eliminate distortion or magnification errors and also to eliminate any effect rotation of the skull would have on the Symphyseal Angle.
Grids were placed on the panoramic radiograph to determine the midsagittal plane, as well as to determine maximum curvature on the lower border of the mandible in the symphysis and the parasymphysis region in order to facilitate drawing of the tangent on the lower border. The maximum difference was found on the lower border in the canine and premolar areas. Tangents were drawn both on the right and left side at the most prominent point. As the patients with condylar asymmetries were eliminated in the study, both the tangents intersected at the midsagittal plane. The angle formed by the tangents was measured at the point of intersection on the midsagittal plane and was named the Symphyseal Angle. The mean SA obtained was 134.1 ± 2.1; for females it was 133.5 ± 3.9 and in males it was 135.1 ± 1.5. This is supported by gender variation obtained in the gonial angle measurement in the study done by Ohm who claimed gender had some effect on the size of the gonial angle.13 The correlation analysis depicted strong negative significant correlation between the SA and the FMA, together with a less significant, but negative, correlation with the BPA.1
Depending upon the significance values, the Symphyseal Angle can be considered as an adjunct to lateral cephalograms to determine the growth pattern of the patient. This study was done using panoramic radiographs which showed no mandibular asymmetry, therefore clinicians should be aware of this fact while evaluating radiographs.
