Comparison of the valuation of lineal measurement between panoramic radiography and periapical radiography.

Objective:To evaluate the differences in accuracy of lineal measurement between panoramic and periapical radiographic images inside the jaw.Method:20 orthodontic cases from 12 to 16 years old permanent teeth patients were selected.5.00 mm steel balls were embedded in their models as the constant reference standard at various positions.By taking panoramic and periapical images and measuring the horizontal and vertical diameter in molar,premolar,canine and incisal regions in the radiographic images,the variation of measurements between different photographing methods at various positions were evaluated and were compared with true values of steel balls respectively.Result:The distortion rate of panoramic measurements was smaller at posterior areas than it at anteriors.Distortion rate of measured values in the periapical radiograph were almost closed to each other except at some anterior areas.The distortion rates of panoramic in horizontal direction were larger than that in vertical direction while the rates were similar in periapical radiograph.Although the measured values which were more closed to trim size could be obtained from panoramic,rather than periapical radiograph,the variation ranges of distortion rate of panoramic was larger.Meanwhile,the distortion rate of the periapical radiography was more invariable except for its larger ranges of variation.Conclusion:It is more reliable to adopt the lineal measurement results of periapical radiograph inside the jaw if the standard reference were taken up.