A. Halse, O. Molven & I. Fristad
Section of Oral Radiology and Section of Endodontics, School of Dentistry, University of Bergen, Bergen, Norway.

Introduction.
Weak visual signals may often, in addition to producing false negative recordings, cause uncertainty to the observer when attempting to make a radiological diagnosis. In addition, early signs of disease, remnants of disease and certain morphological features in bone are difficult to distinguish (Kohler & Zimmer 1967). Endodontists, like other clinicians, are repeatedly faced with such problems. In the evaluation of the apical periodontium, marked visual signals may leave the ob server unclear as to whether the structures represent normal morphology or pathological alterations. Strategies for the radiographic diagnosis of periapical pathosis take this uncertainty into account through calibration of the observers and plans for handling of borderline and disagreement cases (Molander et al. 1998, Trope et al. 1999, Molven et al. 2002a).
Three diagnostic strategies for evaluation of periapical findings are currently in use in epidemiological studies and follow-up investigations. They are: a classification based on the radiographic appearances of the periodontal ligament space (Halse & Molven 1986, Sjogren et al. 1990,Tronstad et al. 2000, Chugal et al. 2001); the periapical index (PAI), a five-group system related to observations made by Brynolf (Orstavik et al. 1986, Trope et al. 1999, Sidaravicius et al. 1999); and a strict definition of periapical disease (Petersson et al. 1989, Weiger et al. 1997, Kvist & Reit1999).
Observers’doubts during evaluation and inter-observer deviations are handled differently in these strategies. In the classification based on radiographic appearances, both disagreement cases and selected borderline cases are discussed jointly during the study, both to reveal diagnostic problems and obtain agreement (Halse&Molven1986, Molven et al.2002a). Using the PAI scoring system, observers are told to assign a higher score when in doubt, and deviations between observers are adjusted or eliminated by approaches to determine ‘true scores’ (Orstavik et al. 1986,Trope et al. 1999). Joint evaluations have also been used (Sidaravicius et al.1999).The use of a strict definition of periapical disease implies that pathoses should only be recorded when observers are sure. Disagreement cases are discussed and agreed jointly (Kvist & Reit1999).
The number of uncertain and disagreement cases or cases subjected to joint evaluations may vary in different studies and are not always given. Irrespective of method, however, decisions in difficult diagnostic situations for man important element of recording and classifying the disease. Such problem cases ought to be presented to other clinicians and researchers. In her thesis on correlation between histological and roentgenological characteristics of the periapical region of maxillary incisors, Brynolf (1967) presented a series of illustrative cases. Supplementary material was presented in another publication (Brynolf 1979). In more recent papers by other investigators, the radiographic picture in deviating cases has not been presented, and thus the refined analyses are not left open for discussion b y others.
We decided, therefore, to present borderline and disagreement cases taken from a methodological study (Molven et al. 2002a). The aim of this paper is to discuss problems related to such cases.

Materials and methods.
The original material, 257 cases, and the methods are presented elsewhere (Molven et al. 2002a). Full agreement between the three observers was found for 73% of the cases, and agreement between three different pairs of observers was 82, 85 and 86%, respectively.
Atotalof32cases (12%) were subjected to joint discussion. They were: three cases that had been given different diagnoses by the three observers; eight cases that had not been given diagnoses owing to substandard radiographs, either by the radiologist (AH) alone or by the two endodontists (OM and IF); 21 cases selected by one of the observers (OM) amongst cases with initial agreement between two observers. Guidelines for selection were:

1. each observer should be represented with deviations from the two others,
2. each classification group should be represented as a deviating diagnosis,
3. special attention should be given to difficulties encountered with the diagnosis of apical periodontitis,
4. different tooth groups and both jaws should be included.

The observers met three times during the methodological study (Molven et al. 2002a) for evaluation and discussion of disagreement and borderline cases.

Agreement after joint evaluation was obtained for all the cases selected for discussion. Twenty-five diagnoses were established and seven cases were rejected owing to substandard radiographs. The rejected cases had all formerly been suggested for rejection, but one case rejected by two observers was given a diagnosis when discussed jointly. Cases from six patients, representing different teeth/roots illustrating rather typical problems discussed during joint evaluation are shown in Figs 1-6.
A tooth that caused frequent problems was the maxillary lateral incisor. The varying morphology of its apical area and varying density of the surrounding bone presented a number of challenges. Figure 1 shows a case with somewhat atypical apical morphology. One observer recorded this initially as a widened periodontal space, emphasizing the impression from using less intense viewing light, simulated in the left illustration. The final consensus diagnosis was, however, normal condition, mostly resulting from viewing conditions simulated in the illustration on the right.
Figure 2 shows a case where the initial suggestions were normal and apical periodontitis. The final diagnosis became apical periodontitis, and the bony destruction was assumed to be located buccal or palatal in relation to the radiographic apex. Comparison with the contralateral tooth gave little support for any of the alternatives.
Figure 3 shows a situation in the mandibular anterior region. From the trabecular pattern in the region, the radiolucency seen in the apical area of the right lateral incisor might represent normal morphology. Two images made with different projections failed, however, to show any movement of the radiolucency relative to the landmarks of the root. The observers here agreed with some uncertainty upon the diagnosis of apical periodontitis.
The initial evaluations of the apical area of the first maxillary premolar shown in Fig. 4 were normal condition and apical periodontitis. The joint discussion settle dupon normal condition, interpreting the radiolucency as a bone marrow space. The absence of a clearly depicted lamina dura in the apical area was considered as being caused by the same anatomical and technical factors as those causing its absence on the distal root surface.
A similar problem is illustrated in Fig. 5. One observer recorded a mesial apical periodontitis, interpreting the radiolucency imaged around the surplus root-filling material as representing a true pathosis. The conclusion of the joint discussion was normal condition, based on the similarity to the rather typical marrow space seen immediately inferior to the distal root and also because portions of the lamina dura were discernible.
The second maxillary molar illustrated in Fig. 6 exhibits a well-delineated radiolucency depicted over the mesial root and the furcation area. Also in this case, the options were either definitely normal or definitely pathological. The final decision was normal condition, based on arguments of similar bony configurations in the edentulous area posterior to this tooth. The differential diagnoses were furcation involvement and osteitis in juxtaposition. These alternatives were discarded especially because of the sharp, cortical borderlines of the radiolucent structure.

Figure 1. Lateral incisor with a typical apical morphology. Final decision: normal condition. See text for supplementary information on this and other illustrated cases.



Figure 2. Lateral incisor (left) interpreted as apical periodontitis, opposite side (right) presented for comparison.


Figure 3. Lateral incisor interpreted as apical periodontitis.


Figure 4. First premolar interpreted as normal condition, i.e. bone marrow space.


Figure 5. First molar with surplus root-filling material at the mesial root interpreted as normal condition.


Figure 6. Second molar with normal periapical condition. The radiolucency depicted over the furcation area was interpreted as normal morphological variant.

Discussion.
This presentation of six difficult disagreement and borderline cases from a radiographic study of endodontically treated teeth aims at adding to an open discussion of diagnostic procedures and problems in endodontology and the classification of periapical findings. A diagnostic procedure should ensure that the classification is valid. Thus, cases diagnosed and classified as ‘successes’ or ‘failures’ should, even when reexamined after an extended period of time, remain in the same categories. The knowledge base might originate from scientific studies supported by histology (Brynolf1967, Green et al.1997) or systematical follow-up as validation (Kaffe & Gratt 1988) or it might be that of experienced clinicians, for example, using the Delphi technique (Stheeman et al.1995).

Anatomical landmarks.
Even in the early literature on the radiological interpretation of the periapical structures relative to endodontic problems, emphasis was put upon alteration in the fine skeletal structures (Simpson1927, Coolidge1937).Eroded versus continuous lamina dura around the apex was considered essential for the diagnosis of initial periapical disease, together with widening of the periodontal space in the same area. These anatomical landmarks are still regarded as fundamental features when identifying early periapical changes. They are pointed out in textbooks both in radiology and endodontics (Gibilisco 1985, Brocklebank1997, Glickman1998, Orstavik1998), and the normal periapical situation forms a natural, basic part of diagnostics groupings (Reit & Hollender 1983, Halse & Molven 1986, Sjogren et al. 1990, Chugal et al. 2001). In the PAI (Orstavik et al. 1986, Trope et al. 1999) however, based on Brynolf’s (1967) extensive study on autopsy material, the score 1 refers to Brynolf’s marginal, nonendodontic cases, grades 1 and 2, and not to illustrations of normal, unaffected periapical situations (Brynolf1979).
The importance of changes in the continuity and shape of the lamina dura and the width and shape of the periodontal ligament space for the identification of non vital teeth has been stressed by Kaffe & Gratt (1988), who evaluated the influence of 18 radiographic features on the consistency and reliability of the radiographic diagnosis of the periapical area. Their advice is that the two features, the lamina dura and the periodontal ligament space, should be emphasized in order to decrease interobserver variations and add to correct radiographic diagnosis.

Periapical lesions.
Amore extensive inflammatory process in the periapical area will in turn create a radiolucency, as viewed from the images caused by destruction and removal of a certain amount of bony mineral. The classical studies of Bender & Seltzer (1961a, 1961b) showed that experimentally created lesions are visible in radiographs only if the junction of cortex and cancellous bone is eroded. As reviewed by Bianchi et al. (1991), several later investigators have come to the same conclusions in similar  experiments. On the other hand, Lee & Messer (1986) have emphasized the importance of alterations in structural details for a correct diagnosis. Periapical lesions confined to cancellous bone were detected in 80% of their cases. These authors point out that the anatomical features of the periapical area appear to promote the visualization of lesions that may not be detected in other locations. They also convincingly argue that the mandibular canalis seen, even though located with in cancellous bone.

Difficult borderline cases.
The fact that minor inflammatory processes present themselves through subtle structural alterations in the periapical area necessitates a thorough observer competency. In general, the transfer of knowledge, skill and experience may be ascertained by current discussion of cases or more systematic calibration. Although such methods are efficient, the exchange of competency is restricted to the same group of clinicians and the procedure and evaluation behind the findings and figures are not openly presented to others. Especially for more complicated cases, the presentation for and discussion by a broader group of specialists might be important. Such cases, like the ones selected from the 32 cases (12% of the total material) subjected to joint discussion, are often identified as difficult borderline cases and must be taken seriously in follow-up studies and epidemiological investigations. If not taken seriously, the validity of the findings might be questioned and their importance reduced.
An approach to solve the problem of a valid grouping of cases has been to accept as ‘abnormal’ only those where the observer feels ‘certain’ (Molander et al. 1998, Kvist & Reit 1999). This will not remove the problem and distinctions must be made between ‘certain’ cases and ‘uncertain’ or borderline cases, a well-known dilemma in endodontology where clinical decisions are frequently based solely on the evaluation of findings from radiographs.

Clinical implications.
The results from research and advice given by the researchers strongly influence treatment decisions made by clinicians. The importance therefore of guiding principles regarding periapical evaluations and findings formulated from a clinician’s perspective has recently been pointed out by Kvist (2001) in the summary of his studies of endodontic retreatment. The identification of periapical lesions forms the basis for the suggested two principles, which is not unexpected. Thus, both researchers and clinicians must decide upon disease/no disease for root-filled teeth and, in practical terms, also establish a success/failure grouping with diagnostic guidelines. As expected, the latter grouping is not only found within older studies (Grahne. n & Hansson 1961, Engstrom et al. 1964) but also presented in recent investigations based on currently used strategies - the three category classification (Tronstad et al. 2000, Chugal et al. 2001, Molven et al. 2002b ,) the PAI index (Sidaravicius et al. 1999, Kirkevang et al. 2001), and the strict definition of periapical disease (Kvist&Reit 1999).
It has been maintained that the PAI de-emphasizes the importance of the observers and may be - or at least has the potential of being - ‘objective’ (Orstavik et al. 1986, Trope et al. 1999, Kirkevang et al. 2001). In our opinion the radiographic evaluation of the apical area that comprises several structural components must always be subjective, and as such is a complex decision-making process not only influenced by scientific factors but is also present on sociological and psychological interacting levels (Reit 1987). One could speculate that computerized image analysis may have the capability of rendering more objective results (White 1996). However, comprehensive studies by Mol (1992) do not support a view that such methods are superior to conventional reading of films. At present this leaves us with the traditional approaches facing difficult borderline cases like the ones presented in this paper. As diagnosticians, we will profit from discussing our problems openly, accepting the limitations inherent in clinical decisions, and the comments and criticism from others.

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