Introduction

Panoramic radiographs were introduced by Yrjo Paatero of the University of Helsinki in 1961 and studied as an essential tool for orthodontic diagnosis and treatment planning. It produces both maxillary and mandibular arches with TMJ and their supporting structures in a single image (Farman, 2007). It is usually the most preferred technique because one single image can reveal all significant diagnostic information acquired by examining all the teeth and basal bone, relatively low radiation exposure and patient comfort (Shahabi, Ramazanzadeh, & Mokhber, 2009). Orthopantomogram (OPG) has been widely used for examining the number and morphological characteristics of teeth present and , caries, impacted teeth, root resorption, ankylosis, the shape of the condylar and coronoid process, temporomandibular joints, sinuses, fractures, cysts, tumours and levels of alveolar bone (Staley & Reske, 2011). The lateral cephalogram introduced in 1931 by Broadbent in the United States and Hofrath in Germany proved to be as both a clinical and a research tool to assess the underlying skeletal disproportions. However, lateral cephalogram will be difficult in measuring the right and left sides of the cranial structure individually, due to overlapping of both the sides especially in asymmetry cases such as hemifacial microsomia, unilateral condylar hyperplasia because it needs precise measurements of structures on each side to diagnose and plan any type surgery or distraction osteogenesis. However, lateral cephalograms cannot be reliably used for the purpose, but this difficulty is not encountered in orthopantomograms (OPGs) (Thailavathy, Kumar, Srinivasan, Loganathan, & Yamini, 2017).

Some already existing literatures such as Shahbaz et al., Nadkerny et al. have reported on the comparison of OPG and lateral cephalogram investigated that gonial angle measurements between OPG and lateral ceph and concluded in his study that panoramic radiograph can be used to assess the gonial angle as precisely as a lateral cephalogram (Nadkerny, Thilagarani, Kumar, & Nadkerny, 2015; Shahbaz et al., 2016).

The validity of angular and linear measurements done on an OPG instead of lateral ceph should be investigated. Thus the purpose of this study is to assess the possible application of OPG for doing craniofacial measurements such as angular and linear measurements of the mandible in skeletal class I pattern with vertical growth patterns and comparing the same measurements made on lateral cephalograms.

Materials and Methods

OPG and lateral cephalogram of 10 patients were selected by using a simple random sampling method. This present retrospective cross-sectional radiographic study was carried out in the Department of Orthodontics in Saveetha Dental College. Ethical clearance was obtained from the Institutional Review Board(IRB) of Saveetha University.The inclusion criteria were class I subjects with vertical growth pattern and high-quality radiographs with adequate sharpness taken by using standard techniques and exposure conditions in natural head position. Patients with a previous history of orthodontic treatment and other orthognathic surgery, any other congenital anomalies or syndromes, facial asymmetry and congenital malformations were excluded.

Statistical Analysis

Mean and SD was calculated for all the parameters of OPG and lateral cephalogram. This statistical analysis was done by using SPSS software ( IBM corp version 13) Independent t-test was performed for comparison of OPG and lateral cephalogram and a paired t-test was performed for comparison between right and left sides of OPG. A probability level of p<0.05 considered statistically significant.

Results and Discussion

Paired t-test was done to find the difference of mean values between the left and right sides of OPGs for all the parameters. There was no statistically significant difference found between right and left sides of OPGs( p> 0.05). Therefore, there is no difference between right and left side values of the OPG parameters.

Independent t-test was done to find the difference of Mean values between OPG and lateral cephalogram for all the parameters. No statistically significant difference was found between OPG and lateral ceph for gonial angle and ramus height (p>0.05). A statistically significant difference was found only for body length when the panoramic measurement is compared with lateral cephalogram (p=0.003).

The present study was performed to assess both the mandibular linear and angular measurements made between OPG and lateral cephalogram in study subjects and found that no statistically significant difference (p> 0.05) was found between right and left sides of OPG (Table 1) and also between OPG and lateral cephalogram in measuring ramus height (p> 0.05) but statistically significant difference was found in measuring body length(p=0.003)(Table 2).

Previously our team had conducted numerous clinical trials (Felicita, 2017), lab animal studies (Jain, Kumar, & Manjula, 2014) and in - vitro studies (Dinesh, Arun, Sundari, Samantha, & Ambika, 2013) over the past five years. The idea for this study stemmed from the current interest in our community.

Ongkosuwito et al. in his study performed same measurements of dry skulls on both OPG and lateral cephalograms and they concluded that linear measurements of the mandible were as close as possible between OPG and lateral cephalogram but only vertical measurements had a better correlation than horizontal measurements of the mandible (Ongkosuwito, Dieleman, Kuijpers-Jagtman, Mulder, & Neck, 2009). Kurt et al. demonstrated that appropriate results could be obtained with panoramic radiographs to evaluate asymmetry of the mandible in Class II subdivision malocclusion patients by measuring condylar and Ramal asymmetry index values and gonial angle measurements (Kurt, Uysal, Sisman, & Ramoglu, 2008). Tronje et al. evaluated the accuracy of panoramic measurements and concluded in his study that if patient is properly positioned then panoramic film is considered as reliable in measuring vertical measurements alone not in the horizontal dimension (Tronje, Welander, McDavid, & Morris, 1981). Larheim and Svanaes et al. also concluded that vertical measurements were reliable on OPGs, but horizontal measurements were clearly more unreliable between OPG and lateral cephalogram (Larheim & Svanaes, 1986). Turp et al. compared the vertical linear measurements of ramus and condyle obtained from OPGs of 25 skulls with direct measurement of the skull and concluded that there was a low correlation between the two (Türp, Vach, Harbich, Alt, & Strub, 1996). Kambylafkas et al. suggested that the panoramic radiograph can be used to evaluate the mandibular ramus height, but measurements will not be as accurate as lateral cephalogram. (Kambylafkas, Murdock, Gilda, Tallents, & Kyrkanides, 2006).

Panoramic radiography can be used to evaluate the ramus height as accurately as a lateral cephalogram, but it was unreliable in measuring body length (Thailavathy et al., 2017). Existing literature supports the role of OPG in doing vertical measurements and this is in concordance to the results of our study. On the contrary, only T puri et al. reported that vertical linear measurement of mandible such as ramus length could not be predicted precisely from OPG (Puri, 2019). Horizontal measurements have been shown to be particularly unreliable because there will be a magnification error at different object depths. Hence overall consensus on favouring OPG for vertical measurements can be agreed upon.

No statistically significant difference was found between OPG and lateral cephalogram in measuring gonial angle (p> 0.05). Some supporting literature such as Mattila et al. in Showed that measurements of gonial angles from the right and left sides of panoramic images were equal to the dry skulls measurements (Mattila, Altonen, & Haavikko, 1977). Shahbaz et al. demonstrated in his study that panoramic radiograph was as accurate as lateral cephalogram in measuring gonial angle (Shahbaz et al., 2016). Nohadani and Ruf et al. observed that there was the highest correlation exists between panoramic and cephalometric radiographs in measuring gonial angle (Nohadani & Ruf, 2008). Puri et al. concluded in his study that panoramic angular measurements can be used to predict the corresponding angular measurements from cephalograms for assessing both dental and skeletal parameters (Puri, 2019).On the contrary, Fischer-Brandies et al. stated that in lateral cephalogram is preferred for measuring gonial angle (Fischer-Brandies, Fischer-Brandies, & Dielert, 1984).

Larheim and Svanaes et al. determined that lateral cephalograms were considered as not reliable in measuring gonial angle but panoramic measurements were comparable to that measurement on the dried mandible (Larheim et al., 1986). Hence the overall consensus of our study is in agreement with the existing literature supporting both OPG and lateral ceph as reliable tools for measuring gonial angle. In panoramic radiography, the focus of projection is different between horizontal and vertical dimension. The rotation centre serves as the functional focus in the horizontal dimension, whereas X-ray source serves as the functional focus in the vertical dimension. Since the source of X-ray serves as the functional focus, the vertical dimension is unaltered by the rotated beam. The limitations of the present study are small sample size, restricted to specific race and ethnicity.

Conclusion

Panoramic radiographs are as comparable as a lateral cephalogram for vertical and angular measurements of the mandible, but it was unreliable in measuring horizontal measurements such as body length of mandible. Although panoramic radiograph has some advantages such as full dental arches can be analysed with less radiation exposure and it is more preferable for mandibular asymmetry cases as right and left sides of the mandible can be clearly analysed due to less superimposition of anatomical structures.

Acknowledgement

Both authors have made an equal contribution for bringing out this research work.

Funding Support

The authors declare that they have no funding support for this study.

Conflict of Interest

The authors declare that they have no conflict of interest.