Modern radiographic methods in the diagnosis of periodontal disease.

For many years, radiographs have been a valuable aid in the diagnosis of periodontal disease and the evaluation of treatment effects. Computer-based image acquisition and processing techniques will now further increase the importance of radiography in periodontal diagnosis. Temporal changes of lesions can be made easily visible by means of subtraction radiography based on digital images. This process requires a pair of images with identical gray-level distributions and projection geometry. The gray-level distribution and perspective projection of images can be corrected by means of digital image processing. A pair of identical images can thus be obtained without mechanical alignment of patient, film, and x-ray source. Algorithms have been developed for automatical determination of the borders of lesions and can subsequently produce quantitative information ranging from simple distance measurements to advanced multidimensional quantitation of image parameters. Accurate volume measurements can be carried out by the utilization of calibration wedges in the image. Image reconstruction procedures, such as tomosynthesis, provide information about the third dimension, which is normally lost in conventional radiographic projections. The buccal and lingual sites of the alveolar crest can be inspected separately. The progress of computer-aided procedures as discussed in this paper appears to have great potential for the improvement of the radiographic diagnosis of periodontal lesions. Especially, the benefits of reproducibility and quantitative evaluation of treatment effects will greatly improve the role of radiography in periodontics.