Skeletal Pattern Assessment by Orthopantomograph

INTRODUCTION

The discovery of X-rays by Wilhelm Conrad Roentgen on Nov. 8^th , 1895, was a boon to health professionals. Dentists were the first among them to pursue the use of radiography in clinical practice. In 1948, Paatero developed panoramic radiography from the medical process of laminography or body section radiography. Today the practice of orthodontics without radiology is unthinkable.

Since the introduction of panoramic radiography, this technique has gained rapidly increasing role in almost all fields of dentistry. The popularity of the technique stemmed from its simplicity of operation, its low radiation dosage when compared to conventional full mouth - periapical survey, and the wide field of projected structure¹.

The need to confirm or negate the existence of skeletal asymmetry is not unusual in orthodontic practice. The panoramic film is most useful as a first step in determination of whether an asymmetry exists. It is important to keep in mind that absolute measurement cannot be performed on the panoramic film. Comparisons from side to side however may be made².

In this study measurements were taken from panoramic radiographs to determine its potentiality for evaluating craniofacial pattern compared to lateral cephalometric radiographs.

MATERIALS AND METHODS

The present study was observational in nature. It involved data collected from pre-treatment panoramic radiographs and lateral cephalograms from 30 skeletal Class II, dental Class II, division 1 patients (12 to 15 years of age) undergoing orthodontic treatment in the Department of Orthodontics and Dentofacial orthopedics, Government Dental College, Bangalore.

Criteria for selection of sample:

1. All patients had skeletal class II, dental Class II, division 1 malocclusion.

2. All patients were between 12 to 15 years of age.

Panoramic radiographs were taken under standard conditions using cephalostat with the clinical Frankfort horizontal plane (FHP) and midfacial planes. The FHP was kept parallel to the floor, while the midfacial plane was in vertical position. To eliminate any possible superimposition of the cervical vertebrae on the image of the teeth, the subjects were required to move a step forward when in the cephalostat. For the standardization of cephalographs, the FHP was oriented parallel to the floor, and the midfacial plane was adjusted vertical to the floor. All the tracings were made on acetate tracing paper using a 0.03” lead pencil. A single operator performed the tracings in a standardized manner to avoid errors due to any inter-operator variations.

RESULTS

The following landmarks, reference planes and angular measurements were used in the study. Student “t' test, Paired “t' tests were performed.

There was no statistically significant difference between male and female subjects, except for the FH/UOP, FH/LOP and FH/L₆ –L₁ (p 0.001), which showed a significant difference. Among the dental parameters compared between OPG and lateral cephalograms, a negative correlation was observed for UOCCL Vs FH /U6- U1 and LOCCL Vs FH / L6-L1 but UOCCL Vs FH /U1, FH /UOP Vs FH / U6-U1, FH / LOP Vs FH / L6-L1 and OMID Vs FH/U1 parameters showed a positive. (fig no 5 & 6)

DISCUSSION

The main aim of this study was to determine whether OPG can be used as an investigative tool in determining skeletal patterns in place of, or in conjunction with the routinely used lateral cephalogram for orthodontic diagnosis. The measurements were selected such that they reflected the angulations and inclinations of the teeth (incisors and molars) and also the skeletal pattern. The bite plate which separated the maxillary and mandibular teeth during the panoramic exposure, enabled to make measurements independently. This bite plate is essential to eliminate the superimposition of corresponding teeth.

Turp et al³stated that vertical linear measurements on the condyle and the ramus made on the OPG are not reliable for patients with macerated skulls. Likewise Larheim and Svanaes⁴ emphasized that the horizontal measurements were unreliable. Therefore only angular measurements were made on the panoramic radiographs.

The Gonial angle (Ar-Go/Go-Me) showed a positive linear correlation with OMAND (Co-Mc/Mc-Me), r = 0.51 (Table 1). This is in accordance with the study by Keiji Matia et al⁵ in which they evaluated the gonial angle (OMAND) from the OPG.

They found that the gonial angle can be determined with accuracy from the OPG as from the lateral cephalogram. Moreover they also showed that the right and left gonial angles can be measured individually, thus avoiding the influence of superimposition seen in lateral cephalograms. The palatal plane to mandibular plane angle (ANS-PNS/Go-Me) from the lateral cephalogram had a negative linear correlation with the OCOND (Co-Mc/Mc-Fme) in the OPG, r = -0.14 (Table 1), indicating that as the PP/MP increased there is a corresponding decrease in the OCOND. This is in accordance with the findings of Okan Akcam et al⁶ , where the PP/MP and OCOND were negatively correlated, r = –0.39. Thus it indicates that the PP/MP can be predicted with a reasonable degree of accuracy using the OCOND from the OPG. But the prediction value R² was 1.9% in the present study, as compared to the 15.6% seen in the study by Okan et al⁶ .The mandibular plane angle (Go-Gn to Sn) in the lateral cephalogram showed a negative linear correlation to the OCOND (Co-Mc/Mc-FMe) in the OPG, r= -0.42 (Table 1). This is similar to the findings of the study by Okan et al⁶ where the MPA in ceph increased with a corresponding decrease in the OCOND of the OPG. (r = -0.45). This decrease can be predicted with accuracy, as shown by the prediction value 17.4% in the present study. The prediction value of the study by Okan et al⁶ was slightly higher (R² = 20.6%). The condylar inclination angle (Co-Go/Go-Me) from the lateral cephalogram showed a positive linear correlation with OMAND (CoMc/Mc-Me) in the OPG, with r = 0.52 (Table 1). This is similar to the study by Okan Akcam et al⁶ , in which they determined that the condylar inclination angle can be predicted with reasonable certainty from the OMAND of the OPG. They also showed a positive correlation between the above two variables with R² (prediction value) of 11.2%. The prediction value between OMAND of the OPG and the condylar inclination angle of the lateral cephalogram in the present study is 27%. Thus the level of prediction being so high the possibility of predicting the cephalometric parameters from panoramic condylar measurements can be considered. This argument coincides with observations of Larheim and Svanaes⁴ that focused on the gonial angle. Their findings on panoramic images of macerated mandibles and measurements done directly on them indicate that gonial angle measurements of both materials showed similar results. The prediction of the lateral cephalogram values from the OPG parameters can be done by using the regression equations obtained through the statistical analyses.

1. Co-Go/Go-Me = 45.569 + 0.55 OMAND. (R ²= 27%) 

2. PP/MP = 31.61 – 0.13 OCOND. (R² = 1.9%) 

3. Go –Gn/Sn = 45.78 – 0.399 OCOND. (R² = 17.4%)

Comparison of OPG parameter between right & left side values for assessing asymmetry. For skeletal parameter comparison of palatal plan mandibular plane and condylar inclination angle between right & left sides in the OPG where statistically insignificant. (p > 0.01) (Table 1).A significance difference p ≤0.05, was found between OCOND- Right and  left in Okan et al⁶ study, whereas no such difference was seen in the present study.OPG can be used to evaluate qualitative assessment of vertical malocclusion, but not the sagittal malocclusion ,since it is a panoramic view.

CONCLUSIONS

1. OPG can be used as an investigative tool, in quantitative assessment of malocclusion.

2. Angular measurements of the OPG can be used as a substitute for corresponding angular measurements from the lateral cephalogram, both for dental as well as skeletal parameters.

3. When using the OPG as the diagnostic tool any one-side measurements can be used instead of measuring both the sides separately.

4. OPG can be used as a screening tool for asymmetries of the facial bones, before going for other detailed investigations.