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The aim of the present study is to clarify the possible application of orthopantomogram (OPG) for evaluating craniofacial specifications such as angular and linear measurements of the mandible by comparing with lateral cephalogram.
OPG and lateral cephalogram were taken from 100 patients of age group 16–35 years from Chettinad Dental College and Research Institute. Linear measurements (body length and ramus height) and angular measurement (gonial angle) were assessed both in lateral cephalogram and OPG. Independent t-test was performed for comparison of OPG and lateral cephalogram using SPSS with a probability level of P < 0.05 considered to be statistically significant.
The results of the present study show that there is no statistically significant difference in ramus height and gonial angle when compared between OPG and lateral cephalogram while statistically significant difference exists for body length between OPG and lateral cephalogram.
It may be concluded that panoramic radiography can be used to determine the gonial angle and ramus height as accurately as a lateral cephalogram. However, clinicians should be vigilant when predicting horizontal measurement from OPGs.
The advent of lateral cephalogram in 1931 by Broadbent in United States and Hofrath in Germany provided both a clinical and a research tool to assess the underlying skeletal disproportions. Since then Orthodontists have explored it widely to analyze dentofacial deformities. However, lateral cephalogram falls short in measuring the right and left sides of the cranial structure individually, due to overlapping of both the sides and interference of superimposed images appearing on the lateral cephalogram.
Asymmetry cases such as hemifacial microsomia, unilateral condylar hyperplasia demand 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. This difficulty is not encountered in orthopantomograms (OPGs).
Posterioanterior cephalogram can also be used in detecting asymmetry in cases. The problem posed by the superimposing structures and the difficulty in reproducing natural head posture makes it less reliable for landmarks.
Since the discovery of panoramic technique by Paatero in 1952, dentists have used it in a variety of dental specialties. Panoramic radiography provides the clinician with a comprehensive view of maxillofacial complex with relatively reduced radiation exposure. By its ability to take a single picture of the entire stomatognathic system-teeth, jaws, temporomandibular joints, sinuses, and panoramic radiography form an essential diagnostic aid. It is frequently used in orthodontic practice to provide important information about the teeth, their axial inclinations, maturation periods, and surrounding tissues. Right and left side structures can be easily visualized individually using OPG, avoiding any overlapping or superimposing structures found on the lateral cephalogram. However, measurements on panoramic radiographs have been called into question because of considerable methodological errors.
The validity of cephalometric measurements when determined on an OPG is still a question to be investigated. Thus, the goal of this study is to clarify the possible application of OPG for evaluating craniofacial specifications such as angular and linear measurements of the mandible by comparing with lateral cephalogram.
OPG and lateral cephalogram of 100 patients of age group 16–35 years were selected from the orthodontic records of Chettinad Dental College and Hospital. The patients with craniofacial malformation and facial asymmetry were excluded from the study. All the radiographs selected were of high quality and sharpness and were taken by the same apparatus with standard exposure conditions and in the Natural Head Position (NHP). The selected radiographs were traced, landmarks located, lines, and angles were drawn, and the following variables measured [Figures [Figures1a1a and andb,b, ,2a2a and andbb].
Gonial angle (degrees) – Angle formed by the intersection of the tangent drawn to lower border of mandible and tangent drawn to ramus.
Both the linear and angular measurements were assessed in lateral cephalogram and OPG by the single investigator. Mean and standard deviation were calculated for all the parameters from OPG and lateral cephalogram. Independent t-test was performed for comparison of OPG and lateral cephalogram using SPSS 21.0 with a probability level of P < 0.05 considered to be statistically significant.
Mean values and standard deviation of left and right sides of OPGs were calculated and tabulated [Table 1] for all the parameters. No statistically significant difference was found. Thus, there is no difference in the right and left side values of the OPG parameters.
Mean and standard deviations were calculated for the gonial angle, ramus height, and mandibular body length measured from lateral ceph, OPGm are tabulated in Tables Tables22--4.4. Mean values of each of the three parameters on the left side of the OPG was compared with the lateral ceph and the same was done for the right side of the OPG. P value is calculated for all three parameters between lateral cephalogram and right and left OPG separately. No statistically significant difference was found between OPG and lateral ceph for gonial angle and ramus height. A significant difference was found when the panoramic measurement is compared with lateral cephalogram for body length.
This study was performed to compare both the mandibular linear and angular measurement between OPG and lateral cephalogram in randomly selected samples. Even though, there are many studies comparing gonial angle measurements between OPG and lateral ceph there are only a few reported studies comparing linear mandibular measurements between OPG and lateral cephalogram. Ongkosuwito et al. studied the dry skull and concluded that an OPG is as reliable as a lateral cephalogram for linear measurements of the mandible, with vertical measurement having a better correlation than horizontal.
Mattila et al. in 197l took measurements of gonial angle on cephalograms, panoramic radiographs and dried skulls. They reported that right and left gonial angles from panoramic images were equal to the angles measured on dry skulls. Fischer-Brandies et al. stated that in determining the gonial angle, the lateral cephalometric radiograph is preferred. However, Larheim and Svanaes indicated that lateral cephalograms did not permit reliable registration of the gonial angle, and the superimposed images created difficulties in recognition and measurement of the individual angles, whereas the gonial angle assessed from a panoramic film was almost identical to that measured on the dried mandible. Akcam et al. compared angular measurements on the OPG to angular measurements on the cephalogram: they found that the OPG can provide information on angular and vertical dimensions of the cranio-facial structures, but that it is not as reliable as a lateral cephalogram. Shahabi et al. compared the external gonial angle determined from the lateral cephalograms and panoramic radiographs in Class I patients. Based on the obtained results, they concluded that panoramic radiography can be used to determine the gonial angle as accurately as a lateral cephalogram. Araki et al. in his study, found that the gonial angle measurements were slightly smaller on the panoramic radiographs than on the lateral cephalometric radiographs.
Fatahi and Babouei evaluated the reliability of the cephalometric measurements when determined from an OPG. Comparison of actual measurements obtained from dry skulls and panoramic radiographic measurements revealed the highest correlation between panoramic and cephalometric radiographs in gonial angle, whereas the least correlation was seen in the length of the mandibular body. Nohadani and Ruf compared longitudinal vertical facial and dentoalveolar changes using panoramic radiographs with measurements on lateral cephalometric radiographs and reported that though OPG delivers a moderate approximation to the situation depicted on lateral cephalogram, panoramic radiographs cannot be recommended for evaluating vertical facial parameter changes during time.
Kurt et al. used OPGs to evaluate mandibular asymmetry in Class II subdivision malocclusion patients by measuring condylar, ramal, condylar and ramal asymmetry index values and gonial angle measurements. They concluded that acceptable results can be achieved with panoramic radiographs. Tronje et al. mathematically calculated the accuracy of panoramic measurements and concluded that within certain limits, the panoramic film can be used for vertical measurements in clinical practice, if the patient is properly positioned. They also concluded that horizontal dimension is unreliable. Larheim and Svanaes also concluded that vertical measurements on the OPGs were reliable, but no comparison was made with lateral cephalograms.
Türp et al. compared the vertical linear measurements on the condyle and the ramus obtained from OPGs of 25 macerated skulls with true values obtained from the direct measurement of the skull and found a low correlation between the two. Kambylafkas et al. in his study suggests that the panoramic radiograph can be used to evaluate total ramal height, but there will be some underdiagnosis.
The results of our study show that there is no statistically significant difference in ramus height and the gonial angle between OPG and lateral cephalogram. Whereas, statistically significant difference exists for body length between OPG and lateral ceph. Thus, OPG can be used to measure the gonial angle and vertical measurements individually on the right and left sides while it may not be reliably used for horizontal measurements, which is in agreement with previous studies.[1,4,11]
Horizontal measurements have been shown to be particularly unreliable because of the nonlinear variation in the magnification at different object depths. In panoramic radiography, the focus of projection in the horizontal dimension differs from that of the vertical dimension. In the horizontal dimension, the rotation center serves as the functional focus, whereas in the vertical dimension the X-ray source serves as the focus. Shape and size distortion of the radiographic images in the vertical plane is function of projection factors. These include factors such as alignment of film, object and X-ray source, object to X-ray source and film to X-ray source distances. Since the X-ray source serves as the functional focus, the vertical dimension is unaffected by the rotation of the beam in the horizontal plane. In the horizontal dimension; however, both projection and motion factors influence size and shape distortion.
Panoramic radiographs may not always have pinpoint accuracy in measuring the angular and vertical measurements, but they do have the advantage of giving a higher diagnostic yield on a single film when compared to lateral cephalogram. They showed an increased coverage of the dental arches with reduced radiation exposure to the patients. Furthermore, OPG being an easier tool for measuring the right and left side of the patient without any interference due to superimposed structures it may be a better choice, especially in asymmetry cases. Though panoramic radiographs are as reliable as a lateral cephalogram for vertical and angular measurements of the mandible, clinicians should be vigilant when predicting horizontal measurement from OPGs.
There are no conflicts of interest.