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 »  Home  »  Endodontic Articles 8  »  Image processing for enhanced observer agreement in the evaluation of periapical bone changes
Image processing for enhanced observer agreement in the evaluation of periapical bone changes
Discussion - References.



Discussion.
The large variation noted amongst clinical and radiographic studies on the outcome of root canal treatment could partly be explained by difficulties in defining and maintaining criteria for radiological evidence of periapical diseases (Reit & Hollender1983). Clinical evaluation of the effect of root canal treatment on periapical lesions is only based upon the symptoms and radiographs. Since clinical symptoms occur infrequently, the incidence of pathologic alterations in the periapical tissue is largely determined by radiographic criteria. However, interpretation of radiographs may be an extremely subjective and inconsistent process despite the great effort that has been devoted to improving radiographic imageing systems. The rates of error in interpretation of radiographs remain alarmingly high. Clearly it is of great importance to be able to follow the radiographic changes within lesion.
The digital subtraction procedure provides a more quantitative and reproducible assessment of periapical lesions than conventional interpretation of radiographs. This study has shown that observer agreement in the evaluation of the effect of root canal treatment on periapical lesions is greater with digital subtraction radiography. In general, digital interpretation was significantly better than the conventional method for the detection of lesions. That means that the probability of detecting a lesion by digital pictures when a lesion is actually present is very high. Our results are in accordance with previous digital imagining studies, showing that the diagnosis of periapical lesions is improved considerably. Kullendorff et al. (1988) reported that subtraction radiography improves the detection of small lesions induced in dry human mandibles in the periapical area. They concluded that the results of their study indicated that the computer-assisted subtraction technique is a promising method to detect early periapical bone lesions of endodontic origin.
The area of diagnostic interest within a radiograph is that which changes over time. Pascon et al. (1987) demonstrated in an animal study that radiographic analysis by subtraction radiography showed hard tissue changes as early as 77 days, and there was a correlation established between radiographic and histologic ?findings.
The interpretation of the results of the present report must consider that the effect of root canal treatment on periapical lesions was based upon conventional radiographs taken at the 1-year-recall when the changes (healing or not) were visible to the human eye. However, the true status of the periapical condition and of the apical seal are unknown and the actual condition might not be reflected by the 1-year radiographs. In a study by Halse et al. (1991) a total of 474 teeth treated with periapical surgery were examined after1year.They concluded that the1-year control provided a valid diagnosis for the majority of cases.
Zakariasen et al. (1984) stated that any diagnostic test must exhibit both validity and reliability to be maximally useful. For correct diagnoses to occur, the diagnostic test must be reliable; i.e. multiple examiners must be able to arrive at the same diagnosis when presented with the same diagnostic data, and the same examiner must agree with himself/herself on repeated readings. Conventional radiographic methods for determining the presence, absence, extension or healing of a lesion in periapical bone are still relatively crude (Tidmarsh 1987). Technological developments such as digital subtraction radiography, however, significantly improve both the validity and reliability of such examination. The advantages of digital subtraction appear to lie in its ability to remove structured noise, thereby allowing detection of changes that the human eye cannot see on conventional radiographs. However, there are several disadvantages to digital subtraction that need to be considered. The most critical component of a subtraction system is geometric reproducibility of the X-ray source to- object relationship.
For many years, the contribution of radiography to the diagnosis of periapical bone lesions has been the subject of extensive research. Nowadays, the implementation of digital image analysis techniques in endodontics can result in greater diagnostic accuracy, because it enables the enhancement of specific features of interest to be carried out using objective methods. Lavelle & Wu (1995) stated that as digital radiographic images are potentially more versatile than conventional radiographs, digital images derived from conventional radiographs offer greater potential benefits for endodontic therapy and other aspects of dentistry than those obtained from intraoral sensors.
Clinically, this may mean that bone changes associated with pulpal pathosis may be detectable at a much earlier time. This may have potential treatment and/or prognosis implications. There are other clinical situations where digital subtraction may be useful in the practice of endodontics. These include the monitoring of bone healing (because subtraction can detect bone additions subsequent to endodontic therapy), the evaluation of internal and eternal resorption and the evaluation of periapical scars present many years after clinically successful endodontic therapy.

References.

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