**2.5 Digital X-rays (RxD)**

The application of digital X-rays (RxD) has gradually increased in dental practice, and the number of professionals who incorporate this technology to their personal practices is on the rise. RxD offer a number of advantages: the image is obtained immediately, with no need for development; the patient is exposed to a lesser radiation dose; and the images are examined using software that moreover allows them to be filed in electronic format, offering different forms of presentation and image measurements (Fig. 5).

In the same way as conventional X-rays, RxD offers low sensitivity and high specificity. We have recorded a sensitivity of 0.61 and a specificity of 0.96, i.e., practically without differences with respect to the conventional X-ray technique. The comparisons of these results with those found in the literature confirm the high specificity and limited sensitivity, though the reported sensitivity range is 0.30-0.70, versus 0.70-0.95 in the case of specificity (Table 3).

Regarding the comparison of both radiological techniques, some authors (Wenzel et al., 1992) consider that there are no differences between conventional X-rays and digital X-rays, in concordance with our own results. In contrast, other studies (Pretty, 2006; Lussi, 1993) have reported slightly greater sensitivity with RxD, and some investigators (McComb & Tam, 2001) consider that this technique improves diagnostic performance in early-stage

How to Diagnose Hidden Caries? The Role of Laser Fluorescence 139

The origin of the fluorescence is not fully clear (Pretty & Maupome, 2004; Tranæus et al., 2005), though it seems unlikely that apatite is responsible for the basal values associated with normal (healthy) enamel (Hibst et al., 2001). The explanation may be the result of the combination of the inorganic matrix with the absorption of organic molecules (Hibst & Paulus, 1999). During the formation of caries an increase in fluorescence is observed related to two processes: demineralization of the tooth, and bacteria with their metabolic products (porphyrin) (Pretty & Maupome, 2004; Tranæus et al., 2005). Most of the fluorescence is induced by the organic components (Tranæus et al., 2005; Hibst et al., 2001), rather than by crystal disintegration and transmission through scantly homogeneous enamel (Farah et al., 2008). This hypothesis is based on the fact that LF does not detect lesions caused in the laboratory with acids not produced as a result of bacterial activity (Pretty & Maupome, 2004). However, LF is able to detect early enamel lesions with a fluorescent stain (porphyrin

The results of the first *in vitro* studies with LF were promising, with high sensitivity and good reproducibility (Lussi et al., 1999). For dentin caries, many investigations have recorded sensitivity values in a very narrow range close to the highest values on the scale (0.79 – 1.0) (Bader & Shugars, 2004; Lussi et al., 1999). Few studies (Bader & Shugars, 2004) have described very low sensitivity (0.19 and 0.26) – such findings being attributable to subjectiveness and errors in the measurement technique during rotation of the instrument tip (Bader & Shugars, 2004; Reis et al., 2006). Although most studies report high sensitivity, the associated specificity is varied. The specificity values of LF in reference to dentin caries in permanent teeth ranges from 0.50 to 1.0 (Lussi et al., 2001; Pretty & Maupome, 2004; Başeren & Gokalp, 2003). Several studies (Bamzahim et al., 2002, 2000; Pereira et al., 2001) have reported near-perfect specificity for LF, thanks to the selection of those teeth with the highest LF readings (Bamzahim et al., 2002), while other authors explain the situation in terms of low sensitivity of the technique (Pereira et al., 2001). In the case of enamel caries the results are contradictory, with either moderate sensitivity ratings associated to high specificity values, or high sensitivity with moderate specificity (Table 4). High sensitivity is in agreement with the observations of previous *in vivo* studies, though without validation based on fissurotomy (Anttonen et al., 2003; Lussi & Francescut, 2003). The above considerations are also consistent with other studies involving histological validation and measurement of third molars (Reis et al., 2006), and with *in vitro* investigations involving third molars stored at -20ºC (Lussi & Hellwig, 2006). In our study (Abalos et al., 2011), high

Fig. 6. Laser fluorescence device (DIAGNOdent, KaVo, Biberach, Germany)

TMPyP) (Mendes et al., 2006).

caries. Further studies involving larger sample sizes are needed to confirm whether RxD improves diagnostic performance with respect to conventional X-rays. Similar considerations apply to VIM versus VI: it makes our work easier, diagnostic performance seems to be better, but analysis of the results fails to reveal statistically significant differences – the latter being taken to represent a difference of over 0.1 in sensitivity/specificity or a difference of over 10% in PPV/NPV.

Fig. 5. Digital X-rays system (Digora Trophy Elitys)


Table 3. Sensitivity and specificity values for the digital X-rays diagnostic evaluation of occlusal caries.

Regarding the predictive usefulness of the technique, in our study (Guerrero, 2011) the PPV of RxD was found to be 97%, i.e., a positive diagnostic reading implies the almost sure presence of caries. However, the same cannot be said when the diagnosis proves negative (i.e., indicative of a healthy tooth), since the proportion of false-negative results is high (NPV 60%).

### **2.6 Laser fluorescence (LF)**

Laser fluorescence (LF) (Fig. 6) is less widely known and used by dental professionals, though it constitutes a necessary complement to the traditional methods. LF therefore deserves a more detailed description in this Chapter. Fluorescence occurs as a result of the interaction between electromagnetic radiation and tissue molecules. When light falls upon the surface of the tooth it penetrates a few millimeters into the tissue, and is reflected towards the tip of a device that measures the fluorescence by means of an electronic system. Two incremental ranges are observed in the fluorescence spectrum: one at 430-450 nm, related to demineralization of the tooth, and another at 590-650 nm, related to the presence of bacteria and their metabolites (Lundberg et al., 2007). Furthermore, there are other elements of organic and inorganic origin that can emit additional fluorescence and thus lead to error in the detection of caries: fluorosis, hypomineralization, bacterial plaque, calculus, proximal surface caries and other stains.

caries. Further studies involving larger sample sizes are needed to confirm whether RxD improves diagnostic performance with respect to conventional X-rays. Similar considerations apply to VIM versus VI: it makes our work easier, diagnostic performance seems to be better, but analysis of the results fails to reveal statistically significant differences – the latter being taken to represent a difference of over 0.1 in

sensitivity/specificity or a difference of over 10% in PPV/NPV.

Fig. 5. Digital X-rays system (Digora Trophy Elitys)

occlusal caries.

**2.6 Laser fluorescence (LF)** 

proximal surface caries and other stains.

**AUTHOR LEVEL STUDY SENSITIVITY SPECIFICITY**  Wenzel 1990 enamel *in vitro* 0.31 0.72 Wenzel 1992 dentin *in vitro* 0.71 0.85 Huysmans 1998 dentin *in vitro* 0.52 - 0.60 0.91 – 0.95 Ashley 1998 dentin *in vitro* 0.19 0.89 Wenzel 2008 dentin *in vitro* 0.31 0.93 Table 3. Sensitivity and specificity values for the digital X-rays diagnostic evaluation of

Regarding the predictive usefulness of the technique, in our study (Guerrero, 2011) the PPV of RxD was found to be 97%, i.e., a positive diagnostic reading implies the almost sure presence of caries. However, the same cannot be said when the diagnosis proves negative (i.e., indicative of a healthy tooth), since the proportion of false-negative results is high (NPV 60%).

Laser fluorescence (LF) (Fig. 6) is less widely known and used by dental professionals, though it constitutes a necessary complement to the traditional methods. LF therefore deserves a more detailed description in this Chapter. Fluorescence occurs as a result of the interaction between electromagnetic radiation and tissue molecules. When light falls upon the surface of the tooth it penetrates a few millimeters into the tissue, and is reflected towards the tip of a device that measures the fluorescence by means of an electronic system. Two incremental ranges are observed in the fluorescence spectrum: one at 430-450 nm, related to demineralization of the tooth, and another at 590-650 nm, related to the presence of bacteria and their metabolites (Lundberg et al., 2007). Furthermore, there are other elements of organic and inorganic origin that can emit additional fluorescence and thus lead to error in the detection of caries: fluorosis, hypomineralization, bacterial plaque, calculus,

Fig. 6. Laser fluorescence device (DIAGNOdent, KaVo, Biberach, Germany)

The origin of the fluorescence is not fully clear (Pretty & Maupome, 2004; Tranæus et al., 2005), though it seems unlikely that apatite is responsible for the basal values associated with normal (healthy) enamel (Hibst et al., 2001). The explanation may be the result of the combination of the inorganic matrix with the absorption of organic molecules (Hibst & Paulus, 1999). During the formation of caries an increase in fluorescence is observed related to two processes: demineralization of the tooth, and bacteria with their metabolic products (porphyrin) (Pretty & Maupome, 2004; Tranæus et al., 2005). Most of the fluorescence is induced by the organic components (Tranæus et al., 2005; Hibst et al., 2001), rather than by crystal disintegration and transmission through scantly homogeneous enamel (Farah et al., 2008). This hypothesis is based on the fact that LF does not detect lesions caused in the laboratory with acids not produced as a result of bacterial activity (Pretty & Maupome, 2004). However, LF is able to detect early enamel lesions with a fluorescent stain (porphyrin TMPyP) (Mendes et al., 2006).

The results of the first *in vitro* studies with LF were promising, with high sensitivity and good reproducibility (Lussi et al., 1999). For dentin caries, many investigations have recorded sensitivity values in a very narrow range close to the highest values on the scale (0.79 – 1.0) (Bader & Shugars, 2004; Lussi et al., 1999). Few studies (Bader & Shugars, 2004) have described very low sensitivity (0.19 and 0.26) – such findings being attributable to subjectiveness and errors in the measurement technique during rotation of the instrument tip (Bader & Shugars, 2004; Reis et al., 2006). Although most studies report high sensitivity, the associated specificity is varied. The specificity values of LF in reference to dentin caries in permanent teeth ranges from 0.50 to 1.0 (Lussi et al., 2001; Pretty & Maupome, 2004; Başeren & Gokalp, 2003). Several studies (Bamzahim et al., 2002, 2000; Pereira et al., 2001) have reported near-perfect specificity for LF, thanks to the selection of those teeth with the highest LF readings (Bamzahim et al., 2002), while other authors explain the situation in terms of low sensitivity of the technique (Pereira et al., 2001). In the case of enamel caries the results are contradictory, with either moderate sensitivity ratings associated to high specificity values, or high sensitivity with moderate specificity (Table 4). High sensitivity is in agreement with the observations of previous *in vivo* studies, though without validation based on fissurotomy (Anttonen et al., 2003; Lussi & Francescut, 2003). The above considerations are also consistent with other studies involving histological validation and measurement of third molars (Reis et al., 2006), and with *in vitro* investigations involving third molars stored at -20ºC (Lussi & Hellwig, 2006). In our study (Abalos et al., 2011), high

How to Diagnose Hidden Caries? The Role of Laser Fluorescence 141

molars, the teeth presumed to be healthy or with enamel caries cannot be validated due to ethical reasons. The authors must assume the standard, without being able to confirm or discard the presence of caries via fissurotomy. As a result, it is not possible to detect the existence of false-negative readings, which are frequent in the visual inspection-based diagnostic procedure used for sample selection. Two options are available in this situation: elimination of the non-validated teeth, whereby the prevalence will be almost 100%, or assumption of the possible existence of false-negative readings in the gold standard. In both cases, the calculations are not precise, and the results must be examined with caution – as pointed out in the literature (Lussi et al., 2001; Heinrich-Weltzien et al., 2003). Only our *in vivo* studies (Abalos et al., 2009; 2011; Guerrero, 2011) involve permanent first and second molars with total sample validation, since the category of healthy teeth or teeth with enamel caries could be validated. The molars were to serve as abutments for fixed prostheses, and could be validated via fissurotomy before being worked upon. An alternative for the use of an imperfect reference standard method is mathematical correction of the values of sensitivity and specificity (Brenner, 1996). This adjustment could approximate the performance obtained in the studies to the actual performance of the methods, increasing the external validity of the study. This procedure has been employed by Matos (2011) for the first time in studies of caries detection. Another alternative to *in vivo* evaluations is the conduction of *in vitro* studies, but with frozen teeth (Lussi & Hellwig, 2006), which allows clinical extrapolation of the results. Other limitations in LF studies are represented by plaque or organic material remains, stains, the degree of tooth dehydration, composite fillings or traces of polishing paste – all of which can affect the LF readings, since they are sources of fluorescence and can therefore give rise to false-positive results. In addition, other factors (Abalos & Jiménez-Planas, 2011) inherent to the tooth such as age, the degree of maturation, and the depth of the pits can influence the

The variation in LF readings found by our group is considerable (Abalos et al., 2009; 2011), in the same way as in other clinical studies (Anttonen et al., 2003; Lussi et al., 2001). However, the mean values show a gradient through the different categories of lesion extent (D0: healthy; D1+2: enamel caries; D3+4: dentin caries) that increases as caries progresses (Lussi et al., 2001). This gradient is observed in both *in vitro* (Başeren & Gokalp, 2003) and in *in vivo* studies (Astvaldsdottir et al., 2004; Anttonen et al., 2003; Heinrich-Weltzien et al., 2003; Lussi et al., 2001; Heinrich-Weltzien et al., 2002), and in both permanent teeth (Astvaldsdottir et al., 2004; Heinrich-Weltzien et al., 2003; Lussi et al., 2001; Heinrich-Weltzien et al., 2002) and temporary teeth (Anttonen et al., 2003; Lussi & Francescut, 2003) – though the values are lower in the case of the primary dentition. In our investigations (Abalos et al., 2009; 2011) LF was seen to be able to distinguish between enamel caries and dentin caries (Abalos et al., 2009), though without being able to discriminate between healthy teeth and teeth with enamel caries (Abalos et al., 2011). The explanation for this latter observation is that the initial enamel lesion does not induce a significant increase in fluorescence when compared with healthy enamel. Likewise, Lussi in 1999 (Lussi et al., 1999) reported that LF does not seem very adequate for detecting minor changes in the enamel. Some studies (Astvaldsdottir et al., 2004) have reported a weak correlation between the LF readings and the depth of the lesion, though this does not suffice to view LF as a method for determining depth. In other words, while LF appears to be able to establish when lesions invade one tissue or other, it is not useful for discriminating depth within one

same tissue, whether enamel or dentin (Lussi et al., 2001; Başeren & Gokalp, 2003).

measurements obtained (Lundberg et al., 2007).

sensitivity was accompanied by limited specificity (0.63) which, although coinciding with the findings of other authors (Bader & Shugars, 2004; Reis et al., 2006) is lower than in others studies (Lussi et al., 2000; Başeren & Gokalp, 2003; Anttonen et al., 2003; Lussi & Hellwig, 2006). Low specificity could be partially due to the fact that we did not eliminate teeth with the presence of brown or dark spots on fissures from the study sample. This low specificity at D1 level (healthy/enamel caries) is less important than at D3 level (enamel caries/dentin caries), where the proportion of false-positive readings can have negative consequences, since it can lead to over-treatment. Table 4 summarizes the results of some representative studies in relation to sensitivity and specificity, though for reasons that will be addressed below, the findings of our investigations (Abalos et al., 2009; 2011) may actually be closest to the true situation.


Table 4. Sensitivity and specificity of laser fluorescence in the diagnosis of occlusal noncavitated caries.

Most studies evaluating LF have been carried out *in vitro* (Tranæus et al., 2005; Stookey & Gonzalez-Cabezas, 2001; Hibst et al., 2001; Bader & Shugars, 2004; Lussi et al., 1999), though there are also a number of *in vivo* studies (Anttonen et al., 2003; Angnes et al., 2005; Heinrich-Weltzien et al., 2003; Lussi et al., 2001; Reis et al., 2006; Abalos et al., 2009; Abalos et al., 2011). The results of *in vitro* studies cannot be extrapolated to *in vivo* conditions, and the limitations of these studies are know. The way in which the teeth are preserved, or the changes in their organic content after extraction, are the main factors inducing alterations in dental tissue fluorescence. The mentioned organic matrix begins to degrade in the second week of preservation of the tooth. When teeth are preserved in formalin, thymol or chlorine (Francescut et al., 2006), the fluorescence value in the occlusal surface decreases rapidly in the first 5 months (Lussi & Francescut, 2003). This in turn implies a drop in the LF values (Lussi et al., 1999) and favors the obtainment of high specificity results. On the other hand, *in vitro* studies make no mention of the age and origin of the samples. *In vivo* studies also pose limitations; in effect, in order to ensure total sample validation, these studies are made in third molars or premolars selected for extraction due to surgical or orthodontic indications. The occlusal anatomy in this case differs from that of the permanent first and second premolars, as a result of which the results must be viewed with caution (Heinrich-Weltzien et al., 2003). In the case of *in vivo* studies conducted in permanent first and second

sensitivity was accompanied by limited specificity (0.63) which, although coinciding with the findings of other authors (Bader & Shugars, 2004; Reis et al., 2006) is lower than in others studies (Lussi et al., 2000; Başeren & Gokalp, 2003; Anttonen et al., 2003; Lussi & Hellwig, 2006). Low specificity could be partially due to the fact that we did not eliminate teeth with the presence of brown or dark spots on fissures from the study sample. This low specificity at D1 level (healthy/enamel caries) is less important than at D3 level (enamel caries/dentin caries), where the proportion of false-positive readings can have negative consequences, since it can lead to over-treatment. Table 4 summarizes the results of some representative studies in relation to sensitivity and specificity, though for reasons that will be addressed below, the findings of our investigations (Abalos et al., 2009; 2011) may actually be closest to

**AUTHOR LEVEL STUDY SENSITIVITY SPECIFICITY**  Lussi 2001 enamel *in vitro* 0.38 - 0.95 0.24 - 0.95 Stookey 2001 enamel *in vitro* 0.42 - 0.87 0.72 – 0.95 Abalos 2011 enamel *in vivo* 0.97 0.63 Lussi 1999 dentin *in vitro* 0.76 – 0.84 0.79 – 0.87 Hibst 2001 dentin *in vitro* 0.92 0.86 Stookey 2001 dentin *in vitro* 0.76 – 0.84 0.79 – 1.00 Heinrich 2003 dentin *in vitro* 0.93 – 0.99 0.13 – 0.63 Reis 2006 dentin *in vitro* 0.71 - 0.78 0.57 - 0.63 Lussi 2001 dentin *in vivo* 0.92 0.86 Agnes 2005 dentin *in vivo* 0.68 - 0.81 0.56 - 0.54 Reis 2006 dentin *in vivo* 0.80 - 0.75 0.43 - 0.52 Abalos 2009 dentin *in vivo* 0.89 0.75 Table 4. Sensitivity and specificity of laser fluorescence in the diagnosis of occlusal non-

Most studies evaluating LF have been carried out *in vitro* (Tranæus et al., 2005; Stookey & Gonzalez-Cabezas, 2001; Hibst et al., 2001; Bader & Shugars, 2004; Lussi et al., 1999), though there are also a number of *in vivo* studies (Anttonen et al., 2003; Angnes et al., 2005; Heinrich-Weltzien et al., 2003; Lussi et al., 2001; Reis et al., 2006; Abalos et al., 2009; Abalos et al., 2011). The results of *in vitro* studies cannot be extrapolated to *in vivo* conditions, and the limitations of these studies are know. The way in which the teeth are preserved, or the changes in their organic content after extraction, are the main factors inducing alterations in dental tissue fluorescence. The mentioned organic matrix begins to degrade in the second week of preservation of the tooth. When teeth are preserved in formalin, thymol or chlorine (Francescut et al., 2006), the fluorescence value in the occlusal surface decreases rapidly in the first 5 months (Lussi & Francescut, 2003). This in turn implies a drop in the LF values (Lussi et al., 1999) and favors the obtainment of high specificity results. On the other hand, *in vitro* studies make no mention of the age and origin of the samples. *In vivo* studies also pose limitations; in effect, in order to ensure total sample validation, these studies are made in third molars or premolars selected for extraction due to surgical or orthodontic indications. The occlusal anatomy in this case differs from that of the permanent first and second premolars, as a result of which the results must be viewed with caution (Heinrich-Weltzien et al., 2003). In the case of *in vivo* studies conducted in permanent first and second

the true situation.

cavitated caries.

molars, the teeth presumed to be healthy or with enamel caries cannot be validated due to ethical reasons. The authors must assume the standard, without being able to confirm or discard the presence of caries via fissurotomy. As a result, it is not possible to detect the existence of false-negative readings, which are frequent in the visual inspection-based diagnostic procedure used for sample selection. Two options are available in this situation: elimination of the non-validated teeth, whereby the prevalence will be almost 100%, or assumption of the possible existence of false-negative readings in the gold standard. In both cases, the calculations are not precise, and the results must be examined with caution – as pointed out in the literature (Lussi et al., 2001; Heinrich-Weltzien et al., 2003). Only our *in vivo* studies (Abalos et al., 2009; 2011; Guerrero, 2011) involve permanent first and second molars with total sample validation, since the category of healthy teeth or teeth with enamel caries could be validated. The molars were to serve as abutments for fixed prostheses, and could be validated via fissurotomy before being worked upon. An alternative for the use of an imperfect reference standard method is mathematical correction of the values of sensitivity and specificity (Brenner, 1996). This adjustment could approximate the performance obtained in the studies to the actual performance of the methods, increasing the external validity of the study. This procedure has been employed by Matos (2011) for the first time in studies of caries detection. Another alternative to *in vivo* evaluations is the conduction of *in vitro* studies, but with frozen teeth (Lussi & Hellwig, 2006), which allows clinical extrapolation of the results. Other limitations in LF studies are represented by plaque or organic material remains, stains, the degree of tooth dehydration, composite fillings or traces of polishing paste – all of which can affect the LF readings, since they are sources of fluorescence and can therefore give rise to false-positive results. In addition, other factors (Abalos & Jiménez-Planas, 2011) inherent to the tooth such as age, the degree of maturation, and the depth of the pits can influence the measurements obtained (Lundberg et al., 2007).

The variation in LF readings found by our group is considerable (Abalos et al., 2009; 2011), in the same way as in other clinical studies (Anttonen et al., 2003; Lussi et al., 2001). However, the mean values show a gradient through the different categories of lesion extent (D0: healthy; D1+2: enamel caries; D3+4: dentin caries) that increases as caries progresses (Lussi et al., 2001). This gradient is observed in both *in vitro* (Başeren & Gokalp, 2003) and in *in vivo* studies (Astvaldsdottir et al., 2004; Anttonen et al., 2003; Heinrich-Weltzien et al., 2003; Lussi et al., 2001; Heinrich-Weltzien et al., 2002), and in both permanent teeth (Astvaldsdottir et al., 2004; Heinrich-Weltzien et al., 2003; Lussi et al., 2001; Heinrich-Weltzien et al., 2002) and temporary teeth (Anttonen et al., 2003; Lussi & Francescut, 2003) – though the values are lower in the case of the primary dentition. In our investigations (Abalos et al., 2009; 2011) LF was seen to be able to distinguish between enamel caries and dentin caries (Abalos et al., 2009), though without being able to discriminate between healthy teeth and teeth with enamel caries (Abalos et al., 2011). The explanation for this latter observation is that the initial enamel lesion does not induce a significant increase in fluorescence when compared with healthy enamel. Likewise, Lussi in 1999 (Lussi et al., 1999) reported that LF does not seem very adequate for detecting minor changes in the enamel. Some studies (Astvaldsdottir et al., 2004) have reported a weak correlation between the LF readings and the depth of the lesion, though this does not suffice to view LF as a method for determining depth. In other words, while LF appears to be able to establish when lesions invade one tissue or other, it is not useful for discriminating depth within one same tissue, whether enamel or dentin (Lussi et al., 2001; Başeren & Gokalp, 2003).

How to Diagnose Hidden Caries? The Role of Laser Fluorescence 143

value of Az ≥ 0.80 is regarded as acceptable, and would mean that the probability of effectively identifying caries is 80%. ROC analysis shows LF to be a good diagnostic technique in application to enamel caries, with Az = 0.803 (Abalos et al., 2011). These results are somewhat inferior to those reported by other investigators (Stookey & Gonzalez-Cabezas, 2001). For dentin caries Az = 0.85, reflecting good diagnostic reliability. These findings coincide with those of some *in vivo* investigations (Heinrich-Weltzien et al., 2003), but exceed the values of 0.64–0.69 described by other *in vivo / in vitro* studies (Angnes et al.,

Comparison of the different diagnostic tests can be based on their respective sensitivity and specificity performances, which reflect the comparative reliability of each technique. The NPV value for occlusal dentin caries was 87%, with a PPV value of 79%. The concepts of sensitivity and specificity therefore allow us to assess the validity of a given diagnostic test. Both sensitivity and specificity offer information on the probability of obtaining a concrete result or reading (positive or negative), according to the true condition of the patient in relation to the disease. However, when a patient is subjected to a test, the dentist lacks prior information on the true diagnosis, and the question is actually posed from a reverse perspective: in the event of a positive or negative test result, what is the probability that the patient is actually ill or healthy? Thus, the predictive values complement the information provided by sensitivity and specificity. The results obtained reflect a high NPV and an acceptable PPV. Therefore, LF is a complement to those tests offering high specificity and a high PPV. LF is a coadjuvant to VI, and the use of both techniques combined increases the

Qualitative light-induced fluorescence (QLF) is used for the detection and quantification of early-stage caries (Pretty, 2006; McComb & Tam, 2001) and for monitoring demineralization or remineralization of smooth surface lesions (Verdonschot & van der Veen, 2002; Heinrich-Weltzien et al., 2005). The tooth is illuminated by the diffuse blue-green light beam of an argon laser at a wavelength of 488 nm (Tranæus et al., 2005; McComb & Tam, 2001). It can also be illuminated by a xenon microdischarge arc lamp and optic fiber system generating blue light at a wavelength of 370 nm (Pretty, 2006), with conduction by a liquid guide. The images are obtained in a dimmed environment using a portable intraoral video camera, with software processing. These images can be used to calculate lesion size, depth and volume (Tranæus et al., 2005; Zandona & Zero, 2006). The demineralized areas appear as dark zones, since radiation of the carious lesion is lower than that of the healthy enamel (Tranæus et al., 2005). The intensity of the emitted light is correlated to mineral loss and can be quantified

QLF is sensitive and reproducible in quantifying smooth surface caries, though it does not discriminate between lesions confined to the enamel layer and dentin caries (McComb & Tam, 2001). The applicability of this technique appears to be limited by lesion depth (McComb & Tam, 2001) – QLF being effective up to 400 μm in depth, but not beyond. The possibility of adapting the technique to the diagnosis of occlusal caries is under investigation, though few clinical studies have been made to date (Weerheijm et al., 1992; McComb & Tam, 2001). Table 5 shows the sensitivity and specificity data of *in vitro* studies on QLF in application to occlusal dentin caries. This diagnostic technique can be affected by

2005), with histological validation in reference to third molars.

number of correctly diagnosed lesions.

(Verdonschot & van der Veen, 2002).

**2.7 Qualitative light-induced fluorescence (QLF)** 

At present, the cutoff values are based on those established by Lussi in 2001 in the context of a clinical study (Lussi et al., 2001), with standardization as follows: 0-13 for healthy teeth, 14- 20 for enamel caries, and >20 for dentin caries. The results of our group are in concordance with these cutoff values (Abalos et al., 2009; 2011), in the same way as in other clinical studies . Our values (Abalos et al., 2011) for healthy first and second molars assessed *in vivo* range between 0 and 14. Values below 10 in all cases corresponded to healthy fissures. The only previous studies (Başeren & Gokalp, 2003; Sheehy et al., 2001) made to determine the limits in healthy enamel have been conducted *in vitro* (Başeren & Gokalp, 2003) or *in vivo* in third molars (Sheehy et al., 2001), with histological validation. Laser fluorescence readings of >14 in turn can be indicative of enamel caries, while readings of ≥ 20 can mean dentin caries, though without necessarily implying operative intervention. As advised by Lussi (Lussi et al., 2001), in patients with low caries risk, fissure aperture should be indicated at LF readings of ≥ 30.

In contrast to the previously examined techniques, LF is more sensitive than specific, and so implies a greater number of false-positive readings. These readings are normally explained by fluorescence sources unrelated to caries – stained fissures being the main problem facing diagnosis with LF (Angnes et al., 2005; Heinrich-Weltzien et al., 2003) (Fig. 7). The stains contribute an added fluorescence signal that increases the measurement values obtained (Côrtes et al., 2003) by between 5-7 units (Heinrich-Weltzien et al., 2003; Sheehy et al., 2001), and represent a frequent cause of overestimation (Sheehy et al., 2001) and of lessened performance of the test. This must be taken into account in order to adjust or modify the cutoff value. When conducting their studies, investigators must specify the percentage of stained fissures in order to allow improved comparison of the results. In our studies (Abalos et al., 2009; 2011; Guerrero 2011) the percentage was approximately 25%. Cases of underestimation are rare, and any such situations are attributable to a poor measurement technique and failure to have rotated the instrument tip in all directions.

Fig. 7. Stained fissure complicating laser fluorescence (LF) diagnosis.

Receiver operating characteristic (ROC) curves take sensitivity and specificity into account for all the cutoff points, thereby reflecting the global diagnostic capacity of the technique. This analysis also offers the average validity of the method used. Taking Az to represent the area under the ROC curve, Az = 1 would represent perfect diagnostic accuracy. In general, a

At present, the cutoff values are based on those established by Lussi in 2001 in the context of a clinical study (Lussi et al., 2001), with standardization as follows: 0-13 for healthy teeth, 14- 20 for enamel caries, and >20 for dentin caries. The results of our group are in concordance with these cutoff values (Abalos et al., 2009; 2011), in the same way as in other clinical studies . Our values (Abalos et al., 2011) for healthy first and second molars assessed *in vivo* range between 0 and 14. Values below 10 in all cases corresponded to healthy fissures. The only previous studies (Başeren & Gokalp, 2003; Sheehy et al., 2001) made to determine the limits in healthy enamel have been conducted *in vitro* (Başeren & Gokalp, 2003) or *in vivo* in third molars (Sheehy et al., 2001), with histological validation. Laser fluorescence readings of >14 in turn can be indicative of enamel caries, while readings of ≥ 20 can mean dentin caries, though without necessarily implying operative intervention. As advised by Lussi (Lussi et al., 2001), in patients with low caries risk, fissure aperture should be indicated at LF

In contrast to the previously examined techniques, LF is more sensitive than specific, and so implies a greater number of false-positive readings. These readings are normally explained by fluorescence sources unrelated to caries – stained fissures being the main problem facing diagnosis with LF (Angnes et al., 2005; Heinrich-Weltzien et al., 2003) (Fig. 7). The stains contribute an added fluorescence signal that increases the measurement values obtained (Côrtes et al., 2003) by between 5-7 units (Heinrich-Weltzien et al., 2003; Sheehy et al., 2001), and represent a frequent cause of overestimation (Sheehy et al., 2001) and of lessened performance of the test. This must be taken into account in order to adjust or modify the cutoff value. When conducting their studies, investigators must specify the percentage of stained fissures in order to allow improved comparison of the results. In our studies (Abalos et al., 2009; 2011; Guerrero 2011) the percentage was approximately 25%. Cases of underestimation are rare, and any such situations are attributable to a poor measurement

technique and failure to have rotated the instrument tip in all directions.

Fig. 7. Stained fissure complicating laser fluorescence (LF) diagnosis.

Receiver operating characteristic (ROC) curves take sensitivity and specificity into account for all the cutoff points, thereby reflecting the global diagnostic capacity of the technique. This analysis also offers the average validity of the method used. Taking Az to represent the area under the ROC curve, Az = 1 would represent perfect diagnostic accuracy. In general, a

readings of ≥ 30.

value of Az ≥ 0.80 is regarded as acceptable, and would mean that the probability of effectively identifying caries is 80%. ROC analysis shows LF to be a good diagnostic technique in application to enamel caries, with Az = 0.803 (Abalos et al., 2011). These results are somewhat inferior to those reported by other investigators (Stookey & Gonzalez-Cabezas, 2001). For dentin caries Az = 0.85, reflecting good diagnostic reliability. These findings coincide with those of some *in vivo* investigations (Heinrich-Weltzien et al., 2003), but exceed the values of 0.64–0.69 described by other *in vivo / in vitro* studies (Angnes et al., 2005), with histological validation in reference to third molars.

Comparison of the different diagnostic tests can be based on their respective sensitivity and specificity performances, which reflect the comparative reliability of each technique. The NPV value for occlusal dentin caries was 87%, with a PPV value of 79%. The concepts of sensitivity and specificity therefore allow us to assess the validity of a given diagnostic test. Both sensitivity and specificity offer information on the probability of obtaining a concrete result or reading (positive or negative), according to the true condition of the patient in relation to the disease. However, when a patient is subjected to a test, the dentist lacks prior information on the true diagnosis, and the question is actually posed from a reverse perspective: in the event of a positive or negative test result, what is the probability that the patient is actually ill or healthy? Thus, the predictive values complement the information provided by sensitivity and specificity. The results obtained reflect a high NPV and an acceptable PPV. Therefore, LF is a complement to those tests offering high specificity and a high PPV. LF is a coadjuvant to VI, and the use of both techniques combined increases the number of correctly diagnosed lesions.

#### **2.7 Qualitative light-induced fluorescence (QLF)**

Qualitative light-induced fluorescence (QLF) is used for the detection and quantification of early-stage caries (Pretty, 2006; McComb & Tam, 2001) and for monitoring demineralization or remineralization of smooth surface lesions (Verdonschot & van der Veen, 2002; Heinrich-Weltzien et al., 2005). The tooth is illuminated by the diffuse blue-green light beam of an argon laser at a wavelength of 488 nm (Tranæus et al., 2005; McComb & Tam, 2001). It can also be illuminated by a xenon microdischarge arc lamp and optic fiber system generating blue light at a wavelength of 370 nm (Pretty, 2006), with conduction by a liquid guide. The images are obtained in a dimmed environment using a portable intraoral video camera, with software processing. These images can be used to calculate lesion size, depth and volume (Tranæus et al., 2005; Zandona & Zero, 2006). The demineralized areas appear as dark zones, since radiation of the carious lesion is lower than that of the healthy enamel (Tranæus et al., 2005). The intensity of the emitted light is correlated to mineral loss and can be quantified (Verdonschot & van der Veen, 2002).

QLF is sensitive and reproducible in quantifying smooth surface caries, though it does not discriminate between lesions confined to the enamel layer and dentin caries (McComb & Tam, 2001). The applicability of this technique appears to be limited by lesion depth (McComb & Tam, 2001) – QLF being effective up to 400 μm in depth, but not beyond. The possibility of adapting the technique to the diagnosis of occlusal caries is under investigation, though few clinical studies have been made to date (Weerheijm et al., 1992; McComb & Tam, 2001). Table 5 shows the sensitivity and specificity data of *in vitro* studies on QLF in application to occlusal dentin caries. This diagnostic technique can be affected by

How to Diagnose Hidden Caries? The Role of Laser Fluorescence 145

FOTI is more specific than sensitive. Table 6 reports the validity of the test in different *in vitro* studies referred to occlusal caries. In an *in vivo* study with full sample validation, our group (Guerrero, 2011) has recorded a sensitivity of 0.47 and a specificity of 1.0. These data are in line with those reported by other *in vitro* studies (Ashley et al., 1998; Cortes et al.,

**AUTHOR LEVEL STUDY SENSITIVITY SPECIFICITY**  Cortes 2000 enamel *in vitro* 0.74 - 1 0.23 – 0.85 Ashley 1998 enamel *in vitro* 0.21 0.95 Cortes 2000 dentin *in vitro* 0.74 0.85 Ashley 1998 dentin *in vitro* 0.14 0.95 Table 6. Sensitivity and specificity of FOTI in the diagnosis of occlusal non-cavitated caries.

As a coadjutant to visual inspection, FOTI can offer an alternative to X-rays in situations where patient irradiation is not possible. It is therefore interesting to compare both methods. In reference to occlusal caries, some authors (Wenzel et al., 1992) consider transillumination to offer better performance than conventional X-rays in detecting early-stage dentin caries. Cortés (Cortes et al., 2000), in an *in vitro* study, reported greater sensitivity than specificity for FOTI, and superior performance with respect to X-rays, though in application to the diagnosis of enamel caries. Once caries has progressed to the dentin, FOTI proved to be significantly inferior to conventional X-rays (Guerrero, 2011). Regarding the predictive usefulness of the technique, we recorded a NPV of 54% and a PPV of 100%, without false-

However, the fact that FOTI is not routinely used by dental professionals, is not recommended as a technique of choice, and is moreover supported by limited research indicates that the inconveniences which we have observed (Guerrero, 2011) – involving a large proportion of false-negative results – are probably coincident with those of other authors who have studied this technique. The main advantage of FOTI is its optimum PPV performance, which means that any positive reading is almost certainly indicative of an

Digitalization may represent a step forward in transillumination diagnosis. Digital FOTI (DIFOTI) makes use of the digitalized image of a tooth during transillumination, which is analyzed using specific software (Tranæus et al., 2005). The images can be filed, reproduced and studied by different examiners, and may serve to monitor the lesion. Interpretation of the image is where problems are found, however, since the results are not directly quantified by the technique. According to some authors (Pretty & Maupome, 2004; Pretty, 2006), the caried areas can be detected in their early stages with DIFOTI, appearing as dark areas. The results may be superior to those afforded by radiography (Pretty & Maupome, 2004; Pretty, 2006), though further studies are needed in order to confirm this possibility.

To summarize, FOTI in combination with visual inspection may be useful for determining occlusal caries depth, though further *in vivo* studies are needed. While in wait of such studies, we consider that transillumination should not be used for diagnosing hidden dentin caries, due to the low sensitivity of the technique and its poorer results compared with Xrays. However, FOTI in combination with VI should be taken into consideration in those

2000).

positive readings (Guerrero, 2011).

cases where X-rays cannot be obtained.

existing lesion.


the degree of humidity or dryness of the fissures, their stains and morphology and does not appear to distinguish between caries and hypoplasia.

Table 5. Sensitivity and specificity of QLF in the diagnosis of hidden dentin caries.

### **2.8 Fiber-optic transillumination (FOTI)**

Fiber-optic transillumination (FOTI) (Fig. 8) is a qualitative technique introduced in the 1970s. It is based on light transmission through an optic fiber; as the light falls upon the tooth surface, it spreads through the healthy dental tissue. In this context, caried tissue is characterized by an increased organic component, with alteration of the homogeneity of the inorganic component – thereby resulting in a loss of light transmission capacity.

Fig. 8. Fiber-optic transillumination device (DioPower Lamp)

FOTI has been used fundamentally for identifying proximal surface caries (Cortes et al., 2000;), with high specificity and a broader range of sensitivity values (Tranæus et al., 2005). The technique is of great help in diagnosing cracked tooth syndrome (Fig. 9). However, it is little used for diagnosing hidden dentin caries, where moreover few studies have assessed its diagnostic performance, precision and reproducibility.

Fig. 9. Cracked tooth syndrome diagnosed by fiber-optic transillumination (FOTI).

the degree of humidity or dryness of the fissures, their stains and morphology and does not

**AUTHOR LEVEL STUDY SENSITIVITY SPECIFICITY**  Stookey 2001 Dentin *in vitro* 0.49 0.67 Zandona 2006 Dentin *in vitro* 0.61 0.59 Pretty 2004 Dentin *in vitro* 0.77 0.67 McComb 2001 Dentin *in vitro* 0.72-0.76 0.79-0.81

Fiber-optic transillumination (FOTI) (Fig. 8) is a qualitative technique introduced in the 1970s. It is based on light transmission through an optic fiber; as the light falls upon the tooth surface, it spreads through the healthy dental tissue. In this context, caried tissue is characterized by an increased organic component, with alteration of the homogeneity of the

FOTI has been used fundamentally for identifying proximal surface caries (Cortes et al., 2000;), with high specificity and a broader range of sensitivity values (Tranæus et al., 2005). The technique is of great help in diagnosing cracked tooth syndrome (Fig. 9). However, it is little used for diagnosing hidden dentin caries, where moreover few studies have assessed

Fig. 9. Cracked tooth syndrome diagnosed by fiber-optic transillumination (FOTI).

Table 5. Sensitivity and specificity of QLF in the diagnosis of hidden dentin caries.

inorganic component – thereby resulting in a loss of light transmission capacity.

Fig. 8. Fiber-optic transillumination device (DioPower Lamp)

its diagnostic performance, precision and reproducibility.

appear to distinguish between caries and hypoplasia.

**2.8 Fiber-optic transillumination (FOTI)** 

FOTI is more specific than sensitive. Table 6 reports the validity of the test in different *in vitro* studies referred to occlusal caries. In an *in vivo* study with full sample validation, our group (Guerrero, 2011) has recorded a sensitivity of 0.47 and a specificity of 1.0. These data are in line with those reported by other *in vitro* studies (Ashley et al., 1998; Cortes et al., 2000).


Table 6. Sensitivity and specificity of FOTI in the diagnosis of occlusal non-cavitated caries.

As a coadjutant to visual inspection, FOTI can offer an alternative to X-rays in situations where patient irradiation is not possible. It is therefore interesting to compare both methods. In reference to occlusal caries, some authors (Wenzel et al., 1992) consider transillumination to offer better performance than conventional X-rays in detecting early-stage dentin caries. Cortés (Cortes et al., 2000), in an *in vitro* study, reported greater sensitivity than specificity for FOTI, and superior performance with respect to X-rays, though in application to the diagnosis of enamel caries. Once caries has progressed to the dentin, FOTI proved to be significantly inferior to conventional X-rays (Guerrero, 2011). Regarding the predictive usefulness of the technique, we recorded a NPV of 54% and a PPV of 100%, without falsepositive readings (Guerrero, 2011).

However, the fact that FOTI is not routinely used by dental professionals, is not recommended as a technique of choice, and is moreover supported by limited research indicates that the inconveniences which we have observed (Guerrero, 2011) – involving a large proportion of false-negative results – are probably coincident with those of other authors who have studied this technique. The main advantage of FOTI is its optimum PPV performance, which means that any positive reading is almost certainly indicative of an existing lesion.

Digitalization may represent a step forward in transillumination diagnosis. Digital FOTI (DIFOTI) makes use of the digitalized image of a tooth during transillumination, which is analyzed using specific software (Tranæus et al., 2005). The images can be filed, reproduced and studied by different examiners, and may serve to monitor the lesion. Interpretation of the image is where problems are found, however, since the results are not directly quantified by the technique. According to some authors (Pretty & Maupome, 2004; Pretty, 2006), the caried areas can be detected in their early stages with DIFOTI, appearing as dark areas. The results may be superior to those afforded by radiography (Pretty & Maupome, 2004; Pretty, 2006), though further studies are needed in order to confirm this possibility.

To summarize, FOTI in combination with visual inspection may be useful for determining occlusal caries depth, though further *in vivo* studies are needed. While in wait of such studies, we consider that transillumination should not be used for diagnosing hidden dentin caries, due to the low sensitivity of the technique and its poorer results compared with Xrays. However, FOTI in combination with VI should be taken into consideration in those cases where X-rays cannot be obtained.

How to Diagnose Hidden Caries? The Role of Laser Fluorescence 147

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

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

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

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

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

enamel or dentin). Low readings in stained fissures rule out dentin caries.

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

follows:

periodic revisions.

the diagnosis of very early stage lesions.

aperture or periodic revisions or controls.

#### **2.9 Electronic caries monitorization (ECM)**

Electronic caries monitorization (ECM) is based on the high electrical conduction resistance of the hard dental tissues. Enamel is a poor electrical conductor though caried enamel shows increased conductance versus intact enamel (Loesche et al., 1979). Demineralized enamel becomes more porous, fills with ion-containing fluid and minerals from saliva, and therefore exhibits increased electrical conductance (McComb & Tam, 2001).

Two devices have been developed, with tips designed for application to the occlusal surface and for measuring electrical conductance in pits or fissures (Zandona & Zero, 2006). The Electronic Caries Monitor (LODE, Groningen, the Netherlands), in the same way as its predecessor (Vanguard, Electronic Caries Detector, Massachusetts Manufacturing Cooperation Cambridge, MA, USA), was developed for diagnosing occlusal surface caries, and allows the identification of early-stage demineralization lesions. The sensitivity performance in application to permanent premolars and molars varies from 0.67 to 0.96, with specificity values of between 0.71 and 0.98 (Tranæus et al., 2005; Pereira et al., 2001; Lussi et al., 1999). The different reviews of ECM describe similar results, with sensitivity values referred to dentin lesions of 0.58 to 0.97 and specificity values between 0.56 and 0.94. One of the reasons for this range of results may be due to the differences in the way in which the technique is used. The degree of dental tissue hydration may also exert an influence, in the same way as enamel maturation and temperature variations (Tranæus et al., 2005; Pretty, 2006). Table 7 shows the sensitivity and specificity performances recorded from *in vitro* and *in vivo* studies with ECM applied to occlusal caries.


Table 7. Sensitivity and specificity of ECM in the diagnosis of occlusal non-cavitated caries.

#### **2.10 Conclusions of the diagnostic tests**

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 noncavitated 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

Electronic caries monitorization (ECM) is based on the high electrical conduction resistance of the hard dental tissues. Enamel is a poor electrical conductor though caried enamel shows increased conductance versus intact enamel (Loesche et al., 1979). Demineralized enamel becomes more porous, fills with ion-containing fluid and minerals from saliva, and therefore

Two devices have been developed, with tips designed for application to the occlusal surface and for measuring electrical conductance in pits or fissures (Zandona & Zero, 2006). The Electronic Caries Monitor (LODE, Groningen, the Netherlands), in the same way as its predecessor (Vanguard, Electronic Caries Detector, Massachusetts Manufacturing Cooperation Cambridge, MA, USA), was developed for diagnosing occlusal surface caries, and allows the identification of early-stage demineralization lesions. The sensitivity performance in application to permanent premolars and molars varies from 0.67 to 0.96, with specificity values of between 0.71 and 0.98 (Tranæus et al., 2005; Pereira et al., 2001; Lussi et al., 1999). The different reviews of ECM describe similar results, with sensitivity values referred to dentin lesions of 0.58 to 0.97 and specificity values between 0.56 and 0.94. One of the reasons for this range of results may be due to the differences in the way in which the technique is used. The degree of dental tissue hydration may also exert an influence, in the same way as enamel maturation and temperature variations (Tranæus et al., 2005; Pretty, 2006). Table 7 shows the sensitivity and specificity performances recorded

**AUTHOR LEVEL STUDY SENSITIVITY SPECIFICITY**  Ashley 1998 enamel *in vitro* 0.65 0.73 Ekstrand 1997 enamel *in vivo* 0.63 0.73 Lussi 1999 dentin *in vitro* 0.58 - 0.92 0.76 - 0.94 Table 7. Sensitivity and specificity of ECM in the diagnosis of occlusal non-cavitated caries.

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 noncavitated 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

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

**2.9 Electronic caries monitorization (ECM)** 

exhibits increased electrical conductance (McComb & Tam, 2001).

from *in vitro* and *in vivo* studies with ECM applied to occlusal caries.

**2.10 Conclusions of the diagnostic tests** 

diagnosing occlusal caries.

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:


How to Diagnose Hidden Caries? The Role of Laser Fluorescence 149

increased LF readings during follow-up, potentially indicative of dentin involvement,

Treatment should distinguish between active and inactive lesions, since such a distinction is important in management terms. The development of techniques for differentiating between active and inactive lesions is thus seen as a necessity, since very few studies in this field have been published to date (Bader & Shugars, 2004). The general clinician experiences great difficulty in distinguishing between these lesions (Ekstrand et al., 2005). When the band and plaque are removed, the clinical features of the active lesion have been recorded as a dull/opaque white area, which is said to be rough when a probe is moved across the surface. Accordingly, the signs for establishing a differentiation are: a) Whether the lesion was dull/matt or shiny/glossy; and b) The tactile sensation of the lesion to a ball-ended

probe run gently across the surface was recorded as smooth or rough to the probe.

need for fissure aperture and the placement of crack sealant.

According to some studies (Pretty, 2006), laser fluorescence is able to establish differences between the readings corresponding to active and inactive enamel caries in permanent molars. In this sense, LF would be able to serve in monitoring the lesion. However, other studies (Toraman et al., 2008) consider that the technique does not register the changes that occur during remineralization and caries development arrest, and cannot serve for

Following improved oral hygiene, the lesion is no longer active, and there may be remineralization within the lesion and abrasion of the eroded surface enamel during oral hygiene procedures and normal function. This leads to a surface which feels smooth when a probe is gently run across it, and which appears shinier (Thylstrup et al., 1994). Once inactive, monitoring of the lesion should continue. Persistent activity is indicative of the

Laser fluorescence readings of under 20 in the presence of positive visual inspection findings are suggestive of dentin caries. Fissure aperture would be indicated with LF

Enamel aperture with a diamond drill, followed by elimination of the caried dentin with adequate instruments, is indicated in the case of dentin caries. Filling with resin composites or silver amalgam should follow. Ceramic incrustations may be considered in the case of

Both the described intervention protocol and the specified treatments cannot encompass all the possible clinical situations. Likewise, they cannot replace clinician experience and the global vision afforded by all the diagnostic techniques, the tooth and oral conditions, and even the individual conditions of each patient. However, the information provided may serve to establish bases and guidelines for intervention and recommendations fundamented

requires fissure aperture.

monitorization purposes.

**4.4 Dentin monitorization** 

important tooth involvement.

on experience and research.

readings of over 20.

**4.5 Dentin caries** 

**4.3 Enamel caries** 
