Modern dental practice needs diagnostic methods to diagnose caries in the early stages of the disease, and research efforts must focus on satisfying this need. The traditional diagnostic techniques offer high specificity, but with the possibility of false-negative results due to dentin caries. Laser fluorescence (LF) shows high sensitivity, and is able to identify hidden dentin caries in situations where visual inspection (VI) and X-rays are unable to detect the lesions. However, because of its lesser specificity and the low current prevalence of caries in the industrialized world, LF should be used as a coadjutant to VI in diagnosing hidden dentin caries. It has been estimated that an additional 30-50% of non-cavitated occlusal caries can be detected in the early stages with LF. Bitewing X-rays represent a complement to VI, but is only able to detect the lesion once it has advanced in the dentinal tissue. As a result, different studies (Anttonen et al., 2003; Ricketts et al., 1997) consider LF to be more effective than bitewing X-rays as an adjunct to VI in diagnosing occlusal caries.
Based on the results obtained, the combination of LF and VI appears as an interesting option. In effect, the two techniques complement each other, securing superior overall performance, since one (LF) is more sensitive than specific, while the other (VI) is more specific than sensitive. When interpreting the results of diagnostic tests, a negative diagnostic result is sometimes more valuable than a positive diagnostic reading. This can be explained as follows: although clinicians seek values from which caries can be diagnosed, the opposite sometimes apply. In effect, we have observed that LF readings of under 10 will never indicate an actual caried tooth, and LF readings of under 20 in stained fissures or cracks will never indicate or correspond to dentin caries. Thus, a first conclusion could be that in the case of a doubtful VI result with LF values of under 10 involving adequate instrument tip rotation, we must assume that the tissue is healthy, in the same way that LF readings of under 20 in stained fissures do not correspond to dentin caries. LF readings of 10-20 with normal VI findings are indicative of healthy tissue, particularly in the presence of some fissure staining. However, in the differential diagnosis between healthy tissue and enamel caries (D0-D1), over-estimation of the lesion is not particularly important, since the treatment involved is of a preventive nature. LF is a help in VI, particularly when the findings of the latter are not clear and a diagnosis cannot be established. LF moreover acquires an added diagnostic value when its readings are low in stained fissures or high in unstained fissures. All teeth with readings above 14 must be subjected to preventive measures and monitorization or control. In turn, LF readings of over 20 can imply that the lesion has reached the dentin, though the experience of the operator and the patient risk factors must always be taken into account. The most important conclusions of this Chapter, based on our investigations (Abalos et al., 2009; 2011; Guerrero, 2011), can be listed as follows:
1. Visual inspection, with or without magnification, is the method of choice for diagnosing non-cavitated caries. For adequate diagnostic performance, use must be made of the Ekstrand criteria, combining VI with other techniques such as LF. Visual inspection is more specific than sensitive, and so a positive diagnosis requires fissure aperture, while a negative diagnostic interpretation is inconclusive and required periodic revisions.
2. Conventional or digital X-rays constitute a necessary complementary technique. Its high specificity means that in the case of a positive diagnosis, fissure aperture should be carried out, and it can be used to assess the extent of the lesion. X-rays are not useful for the diagnosis of very early stage lesions.
3. Laser fluorescence is a useful technique that serves as an adjunct or complement to visual inspection, offering high sensitivity and acceptable specificity. LF readings of under 10 are indicative of a healthy tooth, while readings of over 20 may indicate dentin invasion - though the definitive interpretation must be made in combination with visual inspection. In turn, readings of 10-20 indicate that lesion monitorization is required. LF is unable to establish the depth of the lesion within the tissue (either enamel or dentin). Low readings in stained fissures rule out dentin caries.
4. Probe exploration is not recommended for diagnosing non-cavitated caries. Fiber-optic transillumination (FOTI) is not a method of choice, since it is scantly sensitive - though it may serve as a complementary technique when X-rays cannot be obtained.
5. The combination of exploratory techniques, together with technical and scientific knowledge, are essential for establishing a correct diagnosis of non-cavitated caries. The individual patient factors must be taken into account in order to indicate fissure aperture or periodic revisions or controls.
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