Influence of changing position of chin in the vertical plane on magnification of panoramic images in different areas of the jaws

Panoramic radiography provides a tomographic image of facial structures, with unequal magnification in different parts of the image, which is considered a disadvantage. In addition, wrong position of the patient results in some blurred images outside the image zone. The aim of this study was to evaluate the effect of a change of 10° in the position of the chin in the vertical plane on magnification of different parts of jaws on panoramic radiographs. In this descriptive cross-sectional study 6 human dry skulls were marked in the central, premolar and molar areas of the maxilla and mandible and the ramus area of the mandible by gutta-percha. Then panoramic images were taken twice from each skull in two positions by tilting them up and down for 10 degrees. The measurements on dry skulls and radiographs were carried out by two viewers independently. Data were analyzed by SPSS 11.5 using t-test and ICC (intra-class correlation coefficient) after magnification was calculated in each area (α = 0.05). In the extended position the anterior areas of the jaws exhibited the greatest magnification in both horizontal and vertical dimensions and the least effect of changing chin position was seen in the posterior area of the mandible. In the flexed position, in all the regions, the magnification in the horizontal dimension was less than one. There was a significant difference between the average magnification in both dimensions and both up and down positions and the mean magnification in the normal position (1.25) (p value < 0.05). In both extended and flexed positions, the magnification in the horizontal and vertical dimensions changes with the greatest changes in the anterior regions of jaws.