Clinical diagnosis of fissure caries with conventional and laser-induced fluorescence techniques

The detection of inconspicuous fissure caries on molars is often a challenge to clinicians, in particular when deciding whether surgical intervention should be performed. Although caries is generally not a life-threatening disease, operative treatments for late-stage disease involve the removal of tooth tissue and are irreversible. In contrast, carious lesions in early stages of disease can be remineralized or arrested by favorable changes in environmental factors such as the presence of fluoride ions and improvement in oral hygiene. An ideal diagnostic test for fissure caries therefore requires frequent recall to monitor caries progression and allow operative treatment at the right time, while being able to detect cases of disease with high sensitivity and exclude disease-free cases with high specificity in order to avoid overtreatment. This in vivo study evaluated the performance of visual examination, radiographic examination, and use of DIAGNOdent in the clinical detection of inconspicuous dentinal fissure caries of permanent molars in young Chinese adults. Our findings suggest that DIAGNOdent has a satisfactory validity, and that combined visual examination and DIAGNOdent is a superior method to others in fissure caries detection.

This study screened more than 1,000 students, of whom 41 had 144 molars showing possible inconspicuous fissure caries. The sample size is satisfactory when compared to those of related clinical studies [2, 9, 13]. Initial visual inspection was chosen as a screening method rather than tactile assessment with probing because the latter approach does not improve the validity of caries detection over visual examination [17]. In addition, probing pressure can damage the demineralized fissure and increase the risk for caries progression [10]. This study had a good inter-examiner agreement for visual examination, which could be attributed to the pilot examination and training before the main study. Other clinical studies have also reported good inter-examiner agreement using Ekstrand’s caries index and examiner training [2, 22].

The low sensitivity and high specificity of visual examination at the V3 level (enamel breakdown) observed in our study agree with the findings of Attrill and Ashley [4]. When we changed the diagnostic level to detecting opacity and discoloration (V1), sensitivity improved but specificity diminished. The Youden index was also higher at the V1 level than at the V3 level, which agrees with the results of previous studies. Still, it is possible that examiners who knew the objectives of this study were likely to make an effort to examine the molars thoroughly, helped by optimal examination conditions, and thus concentrate on diagnosing hidden occlusal caries. This situation may be different from that experienced by general dental practitioners during a full routine clinical examination, when periodontal and oral mucosal conditions are assessed in addition to caries status. In practice, misdiagnoses of dentinal caries as enamel caries by visual inspection alone may be more likely and would allow a dentinal lesion to progress without notice.

Furthermore, radiographic examination was performed on a darker image than usual to improve diagnostic quality. Instead of using a conventional light box to assess images, this study used a 19-inch computer liquid crystal display to enlarge images for better visualization of radiolucency in dental hard tissue. The radiographs were interpreted with caution, bearing in mind the possibility of false-positive diagnoses that might arise from the Mach-band effect (an optical illusion of extra bands between sharp boundaries of light and dark areas) resulting in a tendency to see radiolucency in the dentin at the enamel-dentin junction of teeth with no dentinal caries. In the radiographic examination, the sensitivity was very low, as observed in previous studies [4, 11]; however, the specificity of diagnosing early or small carious lesions in the dentin was very high. Hence, despite the technique’s low sensitivity, dentists in their clinical examinations should always look for occlusal caries in radiographs. This recommendation has also been suggested by Poorterman et al. [21], who found areas of radiolucency beneath half of the sealed fissures of 17-year-olds and beneath a quarter of those of 20-year-olds in a Dutch population. Finally, this study aimed to evaluate conventional rather than digital radiography. Future investigations are needed to test the validity of digital radiography in fissure caries detection, especially with CCD/CMOS sensors, which would offer good contrast and spatial resolution.

This study found inter-examiner agreement to be satisfactory, according to the absolute difference of DIAGNOdent score—that is, more than 80% of the assessments had an absolute difference in DIAGNOdent score of not more than 5. Compared with visual examination, the use of DIAGNOdent required less rigorous training in achieving a good agreement in caries assessment. Kappa statistics for inter-examiner agreement with DIAGNOdent assessment in previous clinical studies have been shown to be less than satisfactory [2, 25]. It has also been noted that caries detection in vivo yields higher DIAGNOdent scores than in vitro [22], especially in pigmented sites [22]. The median DIAGNOdent score in a stained fissure can be 5 to 7 units higher than in a fissure that is opaque or not discolored at a similar fissure depth [11]. Stains in fissures are unlikely to be removed by pumice or a rubber cup before DIAGNOdent assessment. In the laboratory, intrinsic and extrinsic stains can be removed by proteolytic solution such as hypochlorite [20], but this method is not commonly practiced in clinical settings. Furthermore, deep fissures [15] and the presence of calculus and organic debris [14] will also increase the DIAGNOdent score, thereby increasing the rate of false-positives in caries assessment. Despite these shortcomings, we obtained acceptable sensitivity and satisfactory specificity values for DIAGNOdent, and our results are comparable to those of other studies of both permanent and primary teeth [4, 18].

Bader and Shugars [6] found that DIAGNOdent demonstrated greater sensitivity but poorer specificity than visual examination when they reviewed 25 studies, and Ricketts [23] concluded that DIAGNOdent is associated with a greater probability of false-positive diagnoses than visual examination. In contrast, more recent in vivo and in vitro studies have reported that DIAGNOdent has good specificity [22, 13, 25]. As adopted by other researchers [4, 18, 22], a value of 20 was used as our initial cut-off point for performing pit and fissure opening. However, the diagnostic criterion for a positive test result among young adults in fluoridated areas should be stricter to give a lower false-positive rate because the caries’ prevalence is expected to be already low. In their clinical study, Kavvadia and Lagouvardos [13] used a higher cut-off point than is usually recommended for detecting caries in dentin. Likewise, the results of this study showed that the optimal cut-off point should be higher than 20, so as to identify more true negatives (non-dentin caries) and achieve good specificity. We found that DIAGNOdent with a cut-off value of 40 has a sensitivity of 0.70 and specificity of 0.84.

The findings of our ROC analysis are also similar to those of other clinical studies [22, 25]. Some researchers consider ROC analysis to reflect diagnostic performance more comprehensively than sensitivity and specificity, because it indicates overall validity of the assessment. Nevertheless, because this single summary value does not capture alternative options for diagnostic threshold (i.e., the cut-off score for diagnosing occlusal dentin caries), ROC analysis does not have a direct application in clinical diagnostic situations, and clinicians still need to select an appropriate threshold from the many points in the ROC curve. For this reason, some clinicians may prefer to keep using sensitivity and specificity in their comparisons of different diagnostic methods. The ideal caries diagnostic test has sensitivity and specificity values of 1 and an area under the ROC curve of 1, but these parameters never reach 1 in real life and some trade-offs must be made [7]. Youden [30] proposed an index to evaluate the appropriateness of a diagnostic test. The Youden index required for a test to be considered useful is typically more than 0.6, but Baelum et al. [7] concluded that no caries diagnostic test has consistently been shown to fulfill this requirement. This study also found that no diagnostic test or combination of tests fulfilled this requirement, except the combination of visual examination and DIAGNOdent. The combined method of visual examination with the V1 criterion and DIAGNOdent with a cut-off score of 40 had a Youden index of 0.61, and was therefore a superior method of fissure caries detection in this study.

A limitation of this study is that it did not record the lesion depth. Indeed, the reliability and calibration of carious lesion depth is very difficult to perform. DIAGNOdent is more reliable in detecting the presence of dentin caries (qualitative capacity) than the depth of the lesion (quantitative capacity) [1]. Porphyrins, which are synthesized by microorganisms in caries lesions, are the organic molecules mainly responsible for caries fluorescence during DIAGNOdent use [16]. Hence, there is actually a poor correlation between DIAGNOdent score and mineral content [27]. Another limitation is that there is no easy or objective way to decide whether a caries diagnosis is correct or not [7]. Pit and fissure opening by the use of a fine carbide bur was considered the reference standard in this and other studies [4, 9, 13]. However, sound teeth cannot be routinely evaluated in the same way for ethical reasons, because early enamel caries that could be remineralized would be unnecessarily removed.