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Azerbaycan Saytlari

 »  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
Introduction.



K. Nicopoulou-Karayianni, U. Bragger, A. Patrikiou, A. Stassinakis and N. P. Lang
Department of Oral and Radiographic Diagnosis, and Department of Oral Surgery, School of Dental Medicine, University of Athens, Greece.
Department for Periodontology and Fixed Prosthodontics, School of Dental Medicine, University of Berne, Freiburg, Str.7, CH-3010 Berne, Switzerland.


Introduction.
The value of conventional radiographic techniques in the evaluation of periapical lesions is limited. Bender & Seltzer (1961 a,b) and Wengraf (1964) showed that the lesions artificially created in human dry mandibles and maxillas could not be detected radiographically if they were limited to cancellous bone. Ramadan & Mitchell (1962) reported a similar finding and also noted that the removal of the entire buccal or lingual plate did not affect the radiographic architectural pattern of bone. In addition, localized defects superimposed by roots were not seen in most cases. Regan & Mitchell (1963) found 18 periapical radiolucencies in 289 teeth of 57 human cadavers. Lesions were apparent radiographically if the cortical plate was perforated or thinned. Pauls & Trott (1966) reported that defects created in cancellous bone with dental burs could not be detected unless the cortical plate was perforated or extensive destruction of the cortex from the outer or inner surface was present. Even perforation through root sockets into the maxillary sinus in dry skulls was not visible on radiographs (Schwartz & Foster1971).
The size of radiographically observed lesions did not correlate with actual tissue destruction (Bender & Seltzer1961a, b). In general, lesions analyzed clinically or histologically were found to be much larger than when estimated radiographically (Bender et al. 1966, Shoha et al. 1974). Shoha et al. (1974) were able to show artificially created lesions involving only cancellous bone in radiographs of the premolar region in dry skull specimens. From 68 lesions limited to cancellous bone, LeQuire et al. (1977) could detect 57 radiographically. Bender (1982) tested the percentage of mineral bone loss, i.e. required to produce a radiolucent area in dry skulls. It was estimated that a mineralized bone loss of greater than 7% in cortical bone was necessary considering soft tissue X-ray absorption and consistency in radiographic visualization. A value for cancellous bone could not be determined.
The interpretation of periapical structures in dental radiographs is subjective. In the study of Goldman et al. (1972), the same 253 cases that had been examined by six independent examiners previously were re-examined 6-8 months later by three of the original examiners. Each examiner’s results were then compared with his original results. They agreed with themselves between 72 and 88% of the time in various categories. The analysis, however, showed large discrepancies in almost all categories of comparisons. Gelfand et al. (1983) reported an intra-examiner disagreement of 21.8%, using10 cases of the material in Goldman’s study. Only in 50% of the evaluated cases was the inter-examiner agreement greater than 50%. In the study of Duinkerke et al. (1975), the intra-examiner discrepancy in tracing periapical lesions varied between 21 and 37%; the inter-examiner difference was 14-52%. Zakariasen et al. (1984) reported that intraobserver agreement was between 64.5 and 81% and that inter-examiner agreement was only 38%. Using more information by analysing three radiographs taken at different angles, the intraobserver agreement rose from 70 to 87% (Brynolf 1970).
In order to make endodontic diagnosis more reliable and to detect subtle changes in the mineral content of periapical areas, alternative methods have been tested for their ability to improve lesion detection. A comparison between xeroradiography (Gratt et al.1986) and conventional radiographs showed high similarity in the interpretation of periapical areas. Large observer variation with both methods has been reported (Petersson et al. 1984). The interpretation of a normal periapical bone region seemed to be facilitated with xeroradiography, probably because this technique has the advantage of edge enhancement (Gratt et al. 1986). Artefacts may however, interfere with areas of diagnostic interest.
Densitometric analysis distinguished reproducibly areas where bone was removed in dry mandibles, whereas the conventional interpretation of the same material by 10 dentists varied considerably (Duinkerke et al.1977). Interfacing a computer with a densitometer allows the analysis of more scans covering whole films. Such precursors to modern image analysers were described by Ando et al. (1969) in connection with periapical imaging. The density was scanned at 5400- 5600 sampling points. These values were converted to a number between 0 and 255 and then displayed into two different colour levels.
Klein (1967) reported an electronic subtraction technique. Using two ¢film cameras viewing two radiographs, one image could be subtracted electronically from the other. Kassle & Klein (1976) compared television subtraction with viewing box examination of conventional¢films. The subtraction readout enhanced the diagnostic image. Periapical changes, induced in 45 mandibular molar and premolars of seven Beagle dogs, were identified 7- 42 days before they were seen using conventional techniques.
There is currently little literature on any application of digital subtraction radiography to periapical bone changes. Digital subtraction techniques have so far been reported for the diagnosis of periodontal lesions changes in vitro (Kullendorff et al. 1988) and in animal models (Pascon et al. 1987). Kullendorff et al. (1988) evaluated the diagnostic potential of subtraction and conventional radiography to assess periapical bone lesions. The periapical region of dry human mandibles was radiographically examined, subjectively evaluated and measured by 125I absorptiometry before and after the creation of bone defects. There was a higher diagnostic accuracy using the subtraction technique. For a lesion depth corresponding to <2 mm of compact bone, there was a clear difference between the techniques, but for deeper lesions the conventional technique gained force. The subtraction technique was significantly superior for lesion confined to cancellous bone. The statistical difference in the diagnostic utility of subtraction compared with conventional technique was found to be less for lesions of the cortical bone. Therefore, they concluded that subtraction radiography improves the detection of small lesions in the periapical bone area. Pascon et al. (1987) used teeth of two baboons to establish a methodology for the development of predictable periapical lesions. Radiographic analysis by subtraction radiography showed hard tissue changes as early as 7 days. The method predictably developed periapical lesions, which could be monitored by subtraction radiography, and there was a correlation established between radiographic and histologic findings.
The aim of the present study was to assess changes within periapical lesions after root canal treatment by conventional and subtracted digital images in clinical situations.