**1. Introduction**

128 Contemporary Approach to Dental Caries

Ricketts, D.; Kidd, E.; Weerheijm, K. & de Soet, H. (1997). Hidden caries: what is it? Does it

Ricketts, D.N.; Ekstrand, K.R.; Martignon, S.; Ellwood, R.; Alatsaris, M. & Nugent, Z. (2007).

Rodrigues, J.A.; Hug, I.; Diniz, M.B. & Lussi, A. (2008). Performance of fluorescence

Rodrigues, J.A.; Hug, I.; Neuhaus, K.W. & Lussi, A. (2011). Light-emitting diode and laser

Sanden, E.; Koob, A.; Hassfeld, S. Staehle, H.J. & Eickholz, P. (2003). Reliability of digital

Shoiab. L.; Deery, C.; Ricketts, D.N. & Nugent, Z.J. (2009). Validity and reproducibility of

Stookey, G. Should a dental explorer be used to probe suspected carious lesions? No – use of an

Thoms, M. (2006). Detection of intraoral lesions using a fluorescence camera. *Proceedings of* 

van der Stelt, P.F. (2008). Better imaging: the advantages of digital radiography. *Journal of the American Dental Association,* Vol.139, No. Suppl, (June), pp. 7S-13S, ISSN 0002-8177 Varma, S.; Banerjee, A. & Bartlett, D. (2008). An in vivo investigation of associations between

Wenzel, A. (1998). Digital radiography and caries diagnosis. *Dentomaxillofacial Radiology*,

Wenzel, A. (2004). Bitewing and digital bitewing radiography for detection of caries lesions. *Journal of Dental Research*, Vol.83, No. Spec No C, pp. C72-C75, ISSN 0022-0345 Wyne, A.H. & Guile, E.E. (1993). Caries activity indicators. A review. *Indian Journal of Dental* 

Young, D.A. & Featherstone, J.D. (2005). Digital imaging fiber-optic trans-illumination, F-

*SPIE Lasers in Dentistry XII, Vol.*6137, No.5, pp. 1-7, ISSN 0002-8177

*Caries Research,* Vol.42, No.4, (July), pp. 297-304, ISSN 0002-8177

*Research*, Vol.41, No.2, pp. 121-128, ISSN 0002-8177

Vol.16, No.10, pp. 107003-1-107003-5, ISSN 1083-3668

No.3, (June), pp. 170-176, ISSN 0894-8275

465, 468, 470 passim, ISSN 1548-8578

pp. 527-539, ISSN 1079-2104

ISSN 0002-8177

Vol.27, No.1, (January), pp. 3-11, ISSN 0007-1285

*Research,* Vol.4, No.2, (April-June), pp. 39-46, ISSN 0970-9290

65, ISSN 1875-595X

ISSN 0002-8177

exist? Does it matter? *International Dental Journal,* Vol.47, No.5, (October), pp. 259-

Accuracy and reproducibility of conventional radiographic assessment and subtraction radiography in detecting demineralization in occlusal surfaces. *Caries* 

methods, radiographic examination and ICDAS II on occlusal surfaces in vitro.

fluorescence-based devices in detecting occlusal caries. *Journal of Biomedical Optics*,

radiography of interproximal dental caries. *American Journal of Dentistry*, Vol.16,

ICDAS II in primary teeth. *Caries Research*, Vol.43, No.6, (November), pp. 442-448,

explorer can lead to misdiagnosis and disrupt remineralization. *Journal of the American Dental Association*, Vol.136, No.11, (November), pp. 1527, 1529, 1531, ISSN 0002-8177 Strassler, H.E. & Sensi, L.G. (2008). Technology-enhanced caries detection and diagnosis.

*Compendium of Continuing Education in Dentistry,* Vol.29, No.8, (October), pp. 464-

saliva properties, caries prevalence and potential lesion activity in an adult UK population*. Journal of Dentistry*, Vol.36, No.4, (April), pp. 294-299, ISSN 0300-5712 Wenzel, A. (1995). Current trends in radiographic caries imaging. *Oral Surgery, Oral* 

*Medicine, Oral Pathology, Oral Radiology, and Endodontics*, Vol.80, No.5, (November),

speed radiographic film and depth of approximal lesions*. Journal of the American Dental Association*, Vol.136, No.12(December), pp. 1682-1687, ISSN 0002-8177 Zandoná, A.F. & Zero, D.T. (2006). Diagnostic tools for early caries detection. *Journal of the* 

*American Dental Association*, Vol.137, No.12, (December), pp. 1675-1684; quiz 1730,

The diagnosis of pits, grooves and fissures is one of the main challenges facing dentists in their professional activity, since the existence of an intact enamel surface may hide deep caries in dentin. Lesions of this kind were described by Weerheijm et al. (1992) as "hidden caries". Over 70 years ago a high incidence of caries was confirmed in grooves and fissures (Hyat, 1923), in coincidence with more recent observations (Bragamian & Garcia-Godoy, 2009). In order to understand and explain this high incidence and the morphological peculiarities involved, it is essential to know the physiopathology of the tooth and of the carious lesion.

Caries is a "*multifactorial disease causing dissolution of the organic component and demineralization of the inorganic component of the hard dental tissues*" (Bonilla, 1998). In the chronology of this process is must be noted that the enamel is a filtering membrane allowing the transit of substances from the exterior to the interior, and vice versa (Llamas et al., 2000). This is because the enamel contains areas with increased water and organic material contents, such as the lamellae or cracks, striae of Retzius, adamantine rod sheath, inter-rod space, and inter-crystalline areas, among others. These zones allow the flow of acids from bacterial plaque, giving rise to disintegration of the organic material and posteriorly conditioning demineralization of the inorganic component – thus supporting the proteolysis – chelation theory of dental caries. These enamel areas with disintegration of the organic material, and the large structural defects such as cracks, which are rich in organic material, can facilitate the penetration of bacteria into deep areas of the enamel, without the existence of superficial cavitation (Brännstrom et al., 1980).

The unpredictable, irregular and varied morphology of the grooves and fissures is well known and makes it impossible to pre-determine the structure; however, it is known that over 50% of all studied teeth have cracks in the depths of the fissures that facilitate the rapid transit of substances and/or bacteria from the depth of the sulcus to the dentin (Pastor et al., 1998). On furthermore considering that enamel thickness from the depth of the sulcus to the dentin is variable and in some cases inexistent, it can be understood why a carious lesion beginning within a fissure can develop in enamel and even in dentin without any external clinical or morphological signs of caries. This in turn explains how in some cases we can

How to Diagnose Hidden Caries? The Role of Laser Fluorescence 131

The existing means for the diagnosis of non-cavitary occlusal caries of grooves and fissures are diverse in terms of the underlying principles and diagnostic capacity. The techniques can be classified according to the frequency with which they are used: the *most common* are visual inspection (VI) and VI with magnification (VIM), the caries probe (CP), conventional X-rays (Rx) and digital X-rays (RxD); *less common* techniques (though still accessible to clinicians) are fiber-optic transillumination (FOTI and DiFOTI) and laser fluorescence (LF); and finally *unusual or experimental* techniques are those which presently are not generally used in clinical practice or which are still in the experimental phase – their use being confined to certain research settings. These latter techniques include the measurement of tissue electrical conductance, based on the reduction of electrical resistance or impedance that characterizes caried tissue (Pretty, 2006), using the electronic caries monitorization (ECM), while other methods are based on qualitative light-induced fluorescence (QLF) – which uses two types of fluorescence and generates images that can be filed for posterior comparison, with the capacity to determine whether the lesions are active or not. In turn, among the purely experimental techniques, mention should be made of optical coherence tomography (OCT), which generates images in the near-infrared region, and is able to detect

Visual inspection is the most widely used diagnostic method. VI has a long history, but is subjective and depends on the experience of the examiner (Pretty, 2006; Zandona & Zero, 2006). The diagnosis of a cavitated lesion poses no diagnostic difficulty of any kind; it is in the case of the so-called "hidden caries" where doubts arise, together with the impossibility of determining whether a dark fissure presents underlying caries or merely corresponds to surface staining. In their first stages, caries of grooves, pits and fissures appear as a milky or darkish stain indicating demineralization of the walls of the fissure and implying enamel opacity. In addition, there may be decoloration of the dentin through the enamel, as well as defects in the bottom or depth of the pit, which would confirm the diagnosis of dentin caries. Accordingly, clinical inspection is based on evaluation of the transparency changes of the enamel, loss of brightness, an opaque appearance, and integrity of the fissure (Thylstrup et al., 1994; Ekstrand et al., 1997). In order to appreciate these changes, the occlusal surfaces must be clean and dry during inspection of the grooves and fissures. Drying the enamel reduces the refraction index of the inter-rod spaces (from 1.33 in the case of humid or moist demineralized surfaces to 1.0 in the case of dry demineralized surfaces) – this making it possible to easily visualize the opaque appearance of enamel demineralization caused by the bacterial plaque acids (Kidd et al., 1993). We can also evaluate pigmentations, the presence or absence of soft tissues, or changes in enamel texture according to the degree of demineralization. According to some authors (Thylstrup et al., 1994), we are also able to establish whether the caries are active or inactive. The evaluation of these findings must be made following some classifying method or criterion capable of correlating the observed signs to the stage of the lesion. The system developed from the studies of Thylstrup in 1994 (Thylstrup et al., 1994) and posteriorly structured by Ekstrand in 1997 (Ekstrand et al., 1997) and modified in 1998 (Ekstrand et al., 1998) is one of the most widely used options. The criteria established by Ekstrand et al. (1997) are the following: 0 = no or slight change in enamel translucency after prolonged air drying; 1 = opacity or discoloration hardly visible

incipient enamel caries *in vitro* (Ngaotheppitak et al., 2005).

**2. Diagnostic tests** 

**2.1 Visual inspection (VI)** 

observe grooves and fissures that are apparently normal or with a discrete brown or blackish color, but with no cavitations reflecting an incipient or consolidated lesion affecting even the dentin (Fig.1). In view of the above, how can we know if we are dealing with a true initial dentinal carious lesion if the tooth appears to be healthy? Or how can we diagnose something in depth based on the surface appearance? On the other hand, how and when do we decide to open the fissure or not? If we fail to open the fissure dentin caries may exist and progress rapidly; alternatively, a decision to open the fissure may cause us to needlessly damage an intact tooth. We thus face a diagnostic dilemma.

Fig. 1. Non-cavitated occlusal caries with deep dentin involvement.

This problem could be a minor concern if the disorder in question were of low prevalence. However, despite the decrease in the frequency of caries in the industrialized world over the last 20 years (Mejàre et al., 2004), not all clinical forms of caries have evolved equally; indeed, caries of grooves and fissures are those showing the greatest prevalence at the present time, since the most notorious decrease has corresponded to caries of smooth surface (Bagramian & Garcia-Godoy, 2009). The form of presentation has also changed; in effect, enamel presently takes longer in becoming affected, thanks mainly to continuous exposure to fluor. As a result, caries develops more slowly, with preservation of enamel integrity for longer periods of time. At present, caries of grooves and fissures affect between 10-50% of the permanent molars of adolescents (Weerheijm et al., 1992), these being the locations where most carious lesions are found, and non-cavitation persists for a longer period of time. Based on the above, it can be concluded that we are not only facing a diagnostic problem, with a high prevalence in adolescents and young adults, but are also facing a buccodental health problem.

The objective of modern Odontology should be to ensure the prevention of caries, avoiding invasive treatments as far as possible. However, this is only possible if full restitution of the affected tissue is achieved (Hibst et al., 2001). In this context, diagnostic tools should evolve in order to allow us to detect the first signs of enamel demineralization. In other words, the tendency should be to facilitate the early detection of caries, with a view to adopting noninvasive treatments and the corresponding preventive measures. On the other hand, we fundamentally should center on common diagnostic techniques that are accessible to dentists, in order for such strategies to be applicable to routine clinical practice.

#### **2. Diagnostic tests**

130 Contemporary Approach to Dental Caries

observe grooves and fissures that are apparently normal or with a discrete brown or blackish color, but with no cavitations reflecting an incipient or consolidated lesion affecting even the dentin (Fig.1). In view of the above, how can we know if we are dealing with a true initial dentinal carious lesion if the tooth appears to be healthy? Or how can we diagnose something in depth based on the surface appearance? On the other hand, how and when do we decide to open the fissure or not? If we fail to open the fissure dentin caries may exist and progress rapidly; alternatively, a decision to open the fissure may cause us to needlessly

damage an intact tooth. We thus face a diagnostic dilemma.

Fig. 1. Non-cavitated occlusal caries with deep dentin involvement.

facing a buccodental health problem.

This problem could be a minor concern if the disorder in question were of low prevalence. However, despite the decrease in the frequency of caries in the industrialized world over the last 20 years (Mejàre et al., 2004), not all clinical forms of caries have evolved equally; indeed, caries of grooves and fissures are those showing the greatest prevalence at the present time, since the most notorious decrease has corresponded to caries of smooth surface (Bagramian & Garcia-Godoy, 2009). The form of presentation has also changed; in effect, enamel presently takes longer in becoming affected, thanks mainly to continuous exposure to fluor. As a result, caries develops more slowly, with preservation of enamel integrity for longer periods of time. At present, caries of grooves and fissures affect between 10-50% of the permanent molars of adolescents (Weerheijm et al., 1992), these being the locations where most carious lesions are found, and non-cavitation persists for a longer period of time. Based on the above, it can be concluded that we are not only facing a diagnostic problem, with a high prevalence in adolescents and young adults, but are also

The objective of modern Odontology should be to ensure the prevention of caries, avoiding invasive treatments as far as possible. However, this is only possible if full restitution of the affected tissue is achieved (Hibst et al., 2001). In this context, diagnostic tools should evolve in order to allow us to detect the first signs of enamel demineralization. In other words, the tendency should be to facilitate the early detection of caries, with a view to adopting noninvasive treatments and the corresponding preventive measures. On the other hand, we fundamentally should center on common diagnostic techniques that are accessible to

dentists, in order for such strategies to be applicable to routine clinical practice.

The existing means for the diagnosis of non-cavitary occlusal caries of grooves and fissures are diverse in terms of the underlying principles and diagnostic capacity. The techniques can be classified according to the frequency with which they are used: the *most common* are visual inspection (VI) and VI with magnification (VIM), the caries probe (CP), conventional X-rays (Rx) and digital X-rays (RxD); *less common* techniques (though still accessible to clinicians) are fiber-optic transillumination (FOTI and DiFOTI) and laser fluorescence (LF); and finally *unusual or experimental* techniques are those which presently are not generally used in clinical practice or which are still in the experimental phase – their use being confined to certain research settings. These latter techniques include the measurement of tissue electrical conductance, based on the reduction of electrical resistance or impedance that characterizes caried tissue (Pretty, 2006), using the electronic caries monitorization (ECM), while other methods are based on qualitative light-induced fluorescence (QLF) – which uses two types of fluorescence and generates images that can be filed for posterior comparison, with the capacity to determine whether the lesions are active or not. In turn, among the purely experimental techniques, mention should be made of optical coherence tomography (OCT), which generates images in the near-infrared region, and is able to detect incipient enamel caries *in vitro* (Ngaotheppitak et al., 2005).

#### **2.1 Visual inspection (VI)**

Visual inspection is the most widely used diagnostic method. VI has a long history, but is subjective and depends on the experience of the examiner (Pretty, 2006; Zandona & Zero, 2006). The diagnosis of a cavitated lesion poses no diagnostic difficulty of any kind; it is in the case of the so-called "hidden caries" where doubts arise, together with the impossibility of determining whether a dark fissure presents underlying caries or merely corresponds to surface staining. In their first stages, caries of grooves, pits and fissures appear as a milky or darkish stain indicating demineralization of the walls of the fissure and implying enamel opacity. In addition, there may be decoloration of the dentin through the enamel, as well as defects in the bottom or depth of the pit, which would confirm the diagnosis of dentin caries. Accordingly, clinical inspection is based on evaluation of the transparency changes of the enamel, loss of brightness, an opaque appearance, and integrity of the fissure (Thylstrup et al., 1994; Ekstrand et al., 1997). In order to appreciate these changes, the occlusal surfaces must be clean and dry during inspection of the grooves and fissures. Drying the enamel reduces the refraction index of the inter-rod spaces (from 1.33 in the case of humid or moist demineralized surfaces to 1.0 in the case of dry demineralized surfaces) – this making it possible to easily visualize the opaque appearance of enamel demineralization caused by the bacterial plaque acids (Kidd et al., 1993). We can also evaluate pigmentations, the presence or absence of soft tissues, or changes in enamel texture according to the degree of demineralization. According to some authors (Thylstrup et al., 1994), we are also able to establish whether the caries are active or inactive. The evaluation of these findings must be made following some classifying method or criterion capable of correlating the observed signs to the stage of the lesion. The system developed from the studies of Thylstrup in 1994 (Thylstrup et al., 1994) and posteriorly structured by Ekstrand in 1997 (Ekstrand et al., 1997) and modified in 1998 (Ekstrand et al., 1998) is one of the most widely used options. The criteria established by Ekstrand et al. (1997) are the following: 0 = no or slight change in enamel translucency after prolonged air drying; 1 = opacity or discoloration hardly visible

How to Diagnose Hidden Caries? The Role of Laser Fluorescence 133

2006). Some studies do not draw these conclusions, however (Heinrich-Weltzien et al., 2002). In effect, Lussi (Lussi et al., 2001) reported that visual inspection alone does not offer good sensitivity in detecting occlusal dentin caries. The width of the fissure also influences sensitivity; in this sense, a diagnosis is more difficult to establish in the presence of narrow fissures than in the case of wide fissures (Lussi, 1991). *In vivo* studies pose the inconvenience of incomplete sample validation, or the use of samples comprising third molars or premolars, with anatomical features different from those of the permanent first and second molars. Most studies indicate that visual inspection offers low-medium sensitivity and high specificity in the diagnosis of occlusal non-cavitated caries (Kidd et al., 1993; Wenzel et al.,

AUTHOR LEVEL STUDY SENSITIVITY SPECIFICITY Lussi 1993 dentin *in vitro* 0.12 0.93 Ektrand 1997 dentin *in vitro* 0.92 - 0.97 0.85 -0.93 Reis 2006 dentin *in vitro* 0.69 0.88 Ashley 1998 enamel *in vivo* 0.60 0.73 Angnes 2005 dentin *in vivo* 0.75 / 0.68 0.84 / 0.81

In our studies (Abalos et al., 2009, 2011; Guerrero, 2011) of laser fluorescence, we obtained a sensitivity for visual inspection of over 0.70, in application to both enamel caries and dentin caries. In contrast to other authors, we achieved total validation of the sample of first and second molars *in vivo*, since we used teeth that were to be prepared for fixed prostheses. This afforded more realistic sensitivity and specificity values for the studied tests. However, in the case of VI, we consider that our results exceed those obtainable in the real life scenario, since as has been explained in our studies (Abalos et al., 2009, 2011; Guerrero, 2011), in our selection of the sample we aimed to secure a sufficient proportion of teeth that were clearly healthy or with enamel caries – a fact that may have influenced the recorded high sensitivity for VI. However, when using the criteria of Ekstrand (Ekstrand et al., 1997), with drying of the tooth (Tranæus et al., 2005; Ekstrand et al., 1997; Angnes et al., 2005; Reis et al., 2006), the sensitivity of the test increases. Many studies of VI have been published, and the results differ greatly according to the type of methodology used (Bader & Shugars, 2004). Despite this fact, VI is a technique that will continue to be used in routine clinical practice. However, rather than focusing on the true diagnostic performance of VI, which is clearly influenced by the examiner and the inaccessible depth of the fissures, future research should attempt to establish which tests are really useful, and to what extent, as coadjutants

The mentioned moderate sensitivity is accompanied by high specificity (Table 1). In other words, while we must accept the probability of false-negative findings (Costa et al., 2008), the high specificity of the test and its important positive predictive value (PPV) (Guerrero, 2011) point to the advisability of opening all fissures with scores of 3 or 4 on the Ekstrand scale (Fig.2D,E). This is where the true usefulness of the test is found: when signs of caries

Regarding the reproducibility of the test, the studies that determine inter-examiner agreement or concordance (Lussi, 1991; Anttonen et al., 2003; Costa et al., 2008) report kappa

1991; Reis et al., 2006; Heinrich-Weltzien et al., 2002) (Table 1).

Table 1. Sensitivity and specificity values for visual inspection.

to visual inspection.

are identified, caries may very well be present.

on the wet surface, but distinctly visible after air drying; 2 = opacity or discoloration distinctly visible without air drying; 3 = localized enamel breakdown in opaque or discolored enamel and/or grayish discoloration from underlying dentin; and 4 = cavitation in opaque or discolored enamel exposing the dentin (Fig. 2). Other criteria have also been developed, however, such as those of Nyvad (Nyvad et al., 1999), the ICDAS (International Caries Detection and Assessment System (Pitts, 2004), the UniViSS (Universal Visual Scoring System for Caries Detection and Diagnosis) (Kuhnisch et al., 2009), or even the International Consensus Workshop on Caries Clinical Trials (ICW-CCT), where caries activity and inactivity are taken into consideration (Pitts & Stamm, 2004).

Fig. 2. Representative signs of caries in cracks and fissures, according to the Ekstrand criteria.

The sensitivity of visual inspection varies greatly depending on the literature source. Our review of the existing publications yielded values between 0.12 and 0.97. A sensitivity of 0.62 to 0.90 is common when there are visible cavities in the fissures. However, in hidden dentin caries, different studies (Lussi, 1993; Wenzel et al., 1991) have reported sensitivity values as low as 0.12. This low sensitivity is due to the fact that we cannot inspect beneath an apparently healthy enamel layer. Some authors (Ekstrand et al., 1997; Pereira et al., 2001) have obtained high sensitivity values that may be justified in part by elimination of a portion of the study sample due to validation problems or because of the presence of stained fissures. Application of the Ekstrand criteria tends to increase the sensitivity of the test both *in vitro* (Ekstrand et al., 1997; Tranæus et al., 2005) and *in vivo* (Angnes et al., 2005; Reis et al.,

on the wet surface, but distinctly visible after air drying; 2 = opacity or discoloration distinctly visible without air drying; 3 = localized enamel breakdown in opaque or discolored enamel and/or grayish discoloration from underlying dentin; and 4 = cavitation in opaque or discolored enamel exposing the dentin (Fig. 2). Other criteria have also been developed, however, such as those of Nyvad (Nyvad et al., 1999), the ICDAS (International Caries Detection and Assessment System (Pitts, 2004), the UniViSS (Universal Visual Scoring System for Caries Detection and Diagnosis) (Kuhnisch et al., 2009), or even the International Consensus Workshop on Caries Clinical Trials (ICW-CCT), where caries activity and

Fig. 2. Representative signs of caries in cracks and fissures, according to the Ekstrand

The sensitivity of visual inspection varies greatly depending on the literature source. Our review of the existing publications yielded values between 0.12 and 0.97. A sensitivity of 0.62 to 0.90 is common when there are visible cavities in the fissures. However, in hidden dentin caries, different studies (Lussi, 1993; Wenzel et al., 1991) have reported sensitivity values as low as 0.12. This low sensitivity is due to the fact that we cannot inspect beneath an apparently healthy enamel layer. Some authors (Ekstrand et al., 1997; Pereira et al., 2001) have obtained high sensitivity values that may be justified in part by elimination of a portion of the study sample due to validation problems or because of the presence of stained fissures. Application of the Ekstrand criteria tends to increase the sensitivity of the test both *in vitro* (Ekstrand et al., 1997; Tranæus et al., 2005) and *in vivo* (Angnes et al., 2005; Reis et al.,

criteria.

inactivity are taken into consideration (Pitts & Stamm, 2004).

2006). Some studies do not draw these conclusions, however (Heinrich-Weltzien et al., 2002). In effect, Lussi (Lussi et al., 2001) reported that visual inspection alone does not offer good sensitivity in detecting occlusal dentin caries. The width of the fissure also influences sensitivity; in this sense, a diagnosis is more difficult to establish in the presence of narrow fissures than in the case of wide fissures (Lussi, 1991). *In vivo* studies pose the inconvenience of incomplete sample validation, or the use of samples comprising third molars or premolars, with anatomical features different from those of the permanent first and second molars. Most studies indicate that visual inspection offers low-medium sensitivity and high specificity in the diagnosis of occlusal non-cavitated caries (Kidd et al., 1993; Wenzel et al., 1991; Reis et al., 2006; Heinrich-Weltzien et al., 2002) (Table 1).



In our studies (Abalos et al., 2009, 2011; Guerrero, 2011) of laser fluorescence, we obtained a sensitivity for visual inspection of over 0.70, in application to both enamel caries and dentin caries. In contrast to other authors, we achieved total validation of the sample of first and second molars *in vivo*, since we used teeth that were to be prepared for fixed prostheses. This afforded more realistic sensitivity and specificity values for the studied tests. However, in the case of VI, we consider that our results exceed those obtainable in the real life scenario, since as has been explained in our studies (Abalos et al., 2009, 2011; Guerrero, 2011), in our selection of the sample we aimed to secure a sufficient proportion of teeth that were clearly healthy or with enamel caries – a fact that may have influenced the recorded high sensitivity for VI. However, when using the criteria of Ekstrand (Ekstrand et al., 1997), with drying of the tooth (Tranæus et al., 2005; Ekstrand et al., 1997; Angnes et al., 2005; Reis et al., 2006), the sensitivity of the test increases. Many studies of VI have been published, and the results differ greatly according to the type of methodology used (Bader & Shugars, 2004). Despite this fact, VI is a technique that will continue to be used in routine clinical practice. However, rather than focusing on the true diagnostic performance of VI, which is clearly influenced by the examiner and the inaccessible depth of the fissures, future research should attempt to establish which tests are really useful, and to what extent, as coadjutants to visual inspection.

The mentioned moderate sensitivity is accompanied by high specificity (Table 1). In other words, while we must accept the probability of false-negative findings (Costa et al., 2008), the high specificity of the test and its important positive predictive value (PPV) (Guerrero, 2011) point to the advisability of opening all fissures with scores of 3 or 4 on the Ekstrand scale (Fig.2D,E). This is where the true usefulness of the test is found: when signs of caries are identified, caries may very well be present.

Regarding the reproducibility of the test, the studies that determine inter-examiner agreement or concordance (Lussi, 1991; Anttonen et al., 2003; Costa et al., 2008) report kappa

How to Diagnose Hidden Caries? The Role of Laser Fluorescence 135

contribute to a faster evolution of hidden caries (Lundberg et al., 2007). In this sense, despite the use of magnification, visual inspection is far from being able to detect these etiopathogenic factors. In this sense, the visual diagnostic techniques require improvement or combination with other diagnostic methods in order to detect these early or incipient stages of caries. In conclusion, and in agreement with the studies of Forgie (Forgie et al., 2002) regarding the use of magnification in relation to other diagnostic techniques, VIM is the method of choice for the detection of occlusal non-cavitated caries, despite the

Fig. 3. Visual inspection of the occlusal surface of a second premolar (A: real size, and

al., 2005; Hamilton, 2005). Other applications would be contraindicated, however.

Until recently, probe exploration formed part of the diagnostic routine in occlusal caries. Probe entrapment in the grooves and fissures helped in establishing the diagnosis. Although this technique is now contraindicated, some professionals continue to use caries probing (CP). The exploration probe has been evaluated as a diagnostic tool in many studies (Lussi, 1991; Lussi & Francescut, 2003). The sensitivity of CP in the detection of occlusal caries is 0.5-0.6 (Hamilton, 2005), though with high specificity values (Bader et al., 2002). The tip of the probe is unable to reach the bottom of the fissures, because of its thickness and the anatomy of the fissures. The probe tip size varies depending on the manufacturer. This lack of standardization of the tip size can make exploration difficult (Lussi, 1993). In addition, a number of studies (Lussi, 1991; Hibst et al., 2001; Hamilton, 2005) have demonstrated that a sharp-tipped probe can cause damage to recently erupted teeth and produce a cavity in a demineralized zone. As a result, the use of such instruments has been the subject of debate for years. Likewise, CP can transmit *Streptococcus mutans* from a contaminated fissure to a healthy fissure (Loesche et al., 1979). On the other hand, CP in combination with visual inspection (VI) does not improve the overall diagnostic performance of the exploration in application to caries of pits and fissures (Lussi, 1991; Lussi, 1993; McComb & Tam, 2001). Based on the above, the use of a round-tipped probe or periodontal probe alone would be justified for eliminating remnant material within the fissure before VI, and for evaluating the texture of the surface without penetrating the latter (Zandona & Zero, 2006; Ekstrand et

limitations commented above.

B:under x3.5 magnification).

**2.3 Caries probing (CP) or tactile examination** 

(k) values of >0.61 to >0.81. The reported intra-examiner reproducibility (Lussi, 1991; Anttonen et al., 2003; Costa et al., 2008) in turn yields k values of >0.41 to >0.81. This scale was developed by Landis and Koch (Landis & Koch, 1977), who scored the concordance values for the k index from <0 (no concordance) to 0–0.20 (insignificant or slight concordance), 0.21–0.40 (discrete concordance), 0.41–0.60 (moderate concordance), 0.61–0.80 (substantial concordance) and 0.81–1 (near-perfect concordance).

In sum, it is important for dentists to become familiarized with this exploration modality, without being too conditioned by superficially stained fissures that do not meet the specified criteria and which can lead to over-treatment. The prevalence of caries and the potential patient risk are important aspects that must be taken into account. A low caries prevalence with good molar hygiene and no bacterial plaque improve the reliability of the test, since there is a lesser probability of establishing an incorrect diagnosis. Visual inspection is the first method to be used in application to hidden dentin caries. In the case of a positive diagnosis, we should open the fissure and use a probe to explore the hardness of the dentin (Kidd et al., 1996). However, a negative diagnosis does not rule out the existence of caries, and other tests must be used together with VI in such situations – particularly in the presence of stained fissures.

#### **2.2 Visual inspection with magnification (VIM)**

Visual inspection with magnification (VIM) involves all the criteria and arguments defined for visual inspection (VI) without magnification. In the same way as with VI, the reported sensitivity data differ greatly, and can be as low as 0.20 (Lussi, 1993) – though accompanied by high specificity in most studies (Lussi, 1991). Magnification can improve the diagnostic performance of the test (Ekstrand et al., 1998; Lussi & Francescut, 2003). In this context, different studies have compared both methods (Lussi, 1993; Lussi, 1991; Lussi & Francescut, 2003), with the observation of superior sensitivity and specificity for VIM, though without reaching statistically significant differences versus VI. We obtained similar results, with a sensitivity rating for VIM (x2.6 magnification) of 0.76, versus 0.71 for VI (Guerrero, 2011). Our observed specificity (Guerrero, 2011) in turn is high, with a value of 0.84. In line with these results, Lussi (Lussi & Francescut, 2003) reported moderate sensitivity (0.65) and high specificity (0.96). Figure 3 simulates the view we would have of the occlusal surface of a lower second premolar without magnification (i.e., real size) and under x3.5 magnification. We can see that visual examination is easier with VIM; thus, although the literature reports no significant differences in performance between the two techniques, VIM is the preferred option, since it allows better appreciation of the possible signs of caries.

The importance of VI and VIM is attributable to their positive predictive value (PPV), which exceeds 90%(Guerrero 2011). In other words, when a positive diagnosis is established, caries is almost sure to be present. The same cannot be said of a negative diagnosis, however, since the negative predictive value (NPV) of the test is not so high. Therefore, we are unable to rule out the possibility of a false-negative diagnosis, since with this test it is often impossible to examine the depths of the fissures. In this sense, according to Lundberg (Lundberg et al., 2007), in the permanent first molars we observe a relationship between pit depth and bacterial colonization. Specifically, central pits are deeper and more varied in their morphology than less deeper mesial pits. There is an interesting correlation between central pits and colonization by *Streptococcus mutans*, and trapped organic material moreover may

(k) values of >0.61 to >0.81. The reported intra-examiner reproducibility (Lussi, 1991; Anttonen et al., 2003; Costa et al., 2008) in turn yields k values of >0.41 to >0.81. This scale was developed by Landis and Koch (Landis & Koch, 1977), who scored the concordance values for the k index from <0 (no concordance) to 0–0.20 (insignificant or slight concordance), 0.21–0.40 (discrete concordance), 0.41–0.60 (moderate concordance), 0.61–0.80

In sum, it is important for dentists to become familiarized with this exploration modality, without being too conditioned by superficially stained fissures that do not meet the specified criteria and which can lead to over-treatment. The prevalence of caries and the potential patient risk are important aspects that must be taken into account. A low caries prevalence with good molar hygiene and no bacterial plaque improve the reliability of the test, since there is a lesser probability of establishing an incorrect diagnosis. Visual inspection is the first method to be used in application to hidden dentin caries. In the case of a positive diagnosis, we should open the fissure and use a probe to explore the hardness of the dentin (Kidd et al., 1996). However, a negative diagnosis does not rule out the existence of caries, and other tests must be used together with VI in such situations – particularly in

Visual inspection with magnification (VIM) involves all the criteria and arguments defined for visual inspection (VI) without magnification. In the same way as with VI, the reported sensitivity data differ greatly, and can be as low as 0.20 (Lussi, 1993) – though accompanied by high specificity in most studies (Lussi, 1991). Magnification can improve the diagnostic performance of the test (Ekstrand et al., 1998; Lussi & Francescut, 2003). In this context, different studies have compared both methods (Lussi, 1993; Lussi, 1991; Lussi & Francescut, 2003), with the observation of superior sensitivity and specificity for VIM, though without reaching statistically significant differences versus VI. We obtained similar results, with a sensitivity rating for VIM (x2.6 magnification) of 0.76, versus 0.71 for VI (Guerrero, 2011). Our observed specificity (Guerrero, 2011) in turn is high, with a value of 0.84. In line with these results, Lussi (Lussi & Francescut, 2003) reported moderate sensitivity (0.65) and high specificity (0.96). Figure 3 simulates the view we would have of the occlusal surface of a lower second premolar without magnification (i.e., real size) and under x3.5 magnification. We can see that visual examination is easier with VIM; thus, although the literature reports no significant differences in performance between the two techniques, VIM is the preferred

The importance of VI and VIM is attributable to their positive predictive value (PPV), which exceeds 90%(Guerrero 2011). In other words, when a positive diagnosis is established, caries is almost sure to be present. The same cannot be said of a negative diagnosis, however, since the negative predictive value (NPV) of the test is not so high. Therefore, we are unable to rule out the possibility of a false-negative diagnosis, since with this test it is often impossible to examine the depths of the fissures. In this sense, according to Lundberg (Lundberg et al., 2007), in the permanent first molars we observe a relationship between pit depth and bacterial colonization. Specifically, central pits are deeper and more varied in their morphology than less deeper mesial pits. There is an interesting correlation between central pits and colonization by *Streptococcus mutans*, and trapped organic material moreover may

option, since it allows better appreciation of the possible signs of caries.

(substantial concordance) and 0.81–1 (near-perfect concordance).

the presence of stained fissures.

**2.2 Visual inspection with magnification (VIM)** 

contribute to a faster evolution of hidden caries (Lundberg et al., 2007). In this sense, despite the use of magnification, visual inspection is far from being able to detect these etiopathogenic factors. In this sense, the visual diagnostic techniques require improvement or combination with other diagnostic methods in order to detect these early or incipient stages of caries. In conclusion, and in agreement with the studies of Forgie (Forgie et al., 2002) regarding the use of magnification in relation to other diagnostic techniques, VIM is the method of choice for the detection of occlusal non-cavitated caries, despite the limitations commented above.

Fig. 3. Visual inspection of the occlusal surface of a second premolar (A: real size, and B:under x3.5 magnification).

#### **2.3 Caries probing (CP) or tactile examination**

Until recently, probe exploration formed part of the diagnostic routine in occlusal caries. Probe entrapment in the grooves and fissures helped in establishing the diagnosis. Although this technique is now contraindicated, some professionals continue to use caries probing (CP). The exploration probe has been evaluated as a diagnostic tool in many studies (Lussi, 1991; Lussi & Francescut, 2003). The sensitivity of CP in the detection of occlusal caries is 0.5-0.6 (Hamilton, 2005), though with high specificity values (Bader et al., 2002). The tip of the probe is unable to reach the bottom of the fissures, because of its thickness and the anatomy of the fissures. The probe tip size varies depending on the manufacturer. This lack of standardization of the tip size can make exploration difficult (Lussi, 1993). In addition, a number of studies (Lussi, 1991; Hibst et al., 2001; Hamilton, 2005) have demonstrated that a sharp-tipped probe can cause damage to recently erupted teeth and produce a cavity in a demineralized zone. As a result, the use of such instruments has been the subject of debate for years. Likewise, CP can transmit *Streptococcus mutans* from a contaminated fissure to a healthy fissure (Loesche et al., 1979). On the other hand, CP in combination with visual inspection (VI) does not improve the overall diagnostic performance of the exploration in application to caries of pits and fissures (Lussi, 1991; Lussi, 1993; McComb & Tam, 2001). Based on the above, the use of a round-tipped probe or periodontal probe alone would be justified for eliminating remnant material within the fissure before VI, and for evaluating the texture of the surface without penetrating the latter (Zandona & Zero, 2006; Ekstrand et al., 2005; Hamilton, 2005). Other applications would be contraindicated, however.

How to Diagnose Hidden Caries? The Role of Laser Fluorescence 137

Regarding the predictive value of the technique, our group (Guerrero, 2011) has recorded a PPV of 100%, suggesting that a positive diagnosis implies the existence of caries, since falsepositive interpretations are very unlikely. In turn, we recorded a NPV of 59%, i.e., normal Xray findings do not discard the possibility that an occlusal lesion may have invaded dentin. In relation to the inter-examiner reproducibility of the technique, the results are varied and range from kappa index (k) values of 0.39 (weak concordance) to 0.95 (near-perfect concordance) (Angnes et al., 2005; Costa et al., 2008; Cortes et al., 2000) – though most

In sum, bitewing X-rays are an obligate diagnostic tool for proximal surface caries and represent a good adjunct in the diagnosis of occlusal caries. Considering that VI results in an important percentage of undetected clinical lesions (Wolwacz et al., 2004), particularly in adolescents (Wenzel et al., 1992), the bitewing X-rays must be carefully evaluated for possible lesions beneath the occlusal enamel. Figure 4 shows caries in dentin with a noncavitated occlusal surface. However, a normal X-ray study does not rule out the presence of

hidden dentin caries, in view of the low sensitivity and NPV of the technique.

Fig. 4. Hidden dentin caries diagnosed from bitewing X-rays (A: dentin caries, B: early

different forms of presentation and image measurements (Fig. 5).

sensitivity range is 0.30-0.70, versus 0.70-0.95 in the case of specificity (Table 3).

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

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

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

studies report substantial concordance values (0.61-0.80).

dentin caries)

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

#### **2.4 Conventional X-rays (Rx)**

Clinical inspection is completed by radiological evaluation. Bitewing X-rays represent the technique of choice for diagnosing proximal surface caries, though they may also be useful for diagnosing occlusal dentin caries (Tranæus et al., 2005; Wenzel et al., 1992). At occlusal level, the X-rays register a tooth thickness beyond the proximal zone, and the lesions are masked by the healthy tissues for a longer period of time (Wenzel et al., 1992). For this reason, from the histological perspective, the lesion is more advanced than suggested by its radiological appearance – a fact that justifies the low sensitivity of the technique. In our studies, the observed sensitivity was 0.57 (Guerrero, 2011), i.e., many existing lesions are not detected. Nevertheless, once again, the specificity is very high. These results imply that negative X-ray findings cannot be taken to rule out dentin caries, though a positive X-ray diagnosis should be taken as an indication for opening the fissure and providing caries treatment. The reviewed *in vivo* and *in vitro* studies (Wenzel et al., 1992, Lussi, 1993; Angnes et al., 2005; Lussi et al., 2001; Ashley et al., 1998; Costa et al., 2008) point to low sensitivity and high specificity, in coincidence with our own results (Table 2). Only studies involving third molars report lesser specificity, possibly due to the difficulty of correctly obtaining Xray projections in this zone.


Table 2. Sensitivity and specificity values for the X-ray diagnostic evaluation of occlusal caries.

The main difficulty of conventional X-ray exploration is the distinction between deep enamel and superficial dentin, due to superpositioning of the healthy vestibular and lingual enamel, which masks the radiotransparency, particularly in early-stage lesions. Carious lesions normally cannot be detected on X-rays until they have extended about 0.5 mm beyond the amelodentinal junction (Kidd et al., 1993). Even with this difficulty, however, *in vitro* studies point to acceptable correlation with the existing histological condition. In this context, Wenzel (Wenzel, 1998) suggested that the *in vitro* diagnostic performance may be better than in the actual clinical setting, i.e., the results obtained in the laboratory may be overestimated. However, other *in vitro* studies indicate that by the time occlusal caries have been identified on the X-rays, demineralization has already extended to the middle third of the dentinal layer, i.e., the deep dentin (Ricketts et al., 1997). Weerheijm (Weerheijm et al., 1992) reported that X-rays are not very effective for diagnosing incipient enamel caries, though the technique is very useful for diagnosing deeper lesions. In this context, conventional X-rays improve the diagnostic capacity of VI by 11%, and moreover help assess the extent of the lesion (Ekstrand et al., 1995).

Clinical inspection is completed by radiological evaluation. Bitewing X-rays represent the technique of choice for diagnosing proximal surface caries, though they may also be useful for diagnosing occlusal dentin caries (Tranæus et al., 2005; Wenzel et al., 1992). At occlusal level, the X-rays register a tooth thickness beyond the proximal zone, and the lesions are masked by the healthy tissues for a longer period of time (Wenzel et al., 1992). For this reason, from the histological perspective, the lesion is more advanced than suggested by its radiological appearance – a fact that justifies the low sensitivity of the technique. In our studies, the observed sensitivity was 0.57 (Guerrero, 2011), i.e., many existing lesions are not detected. Nevertheless, once again, the specificity is very high. These results imply that negative X-ray findings cannot be taken to rule out dentin caries, though a positive X-ray diagnosis should be taken as an indication for opening the fissure and providing caries treatment. The reviewed *in vivo* and *in vitro* studies (Wenzel et al., 1992, Lussi, 1993; Angnes et al., 2005; Lussi et al., 2001; Ashley et al., 1998; Costa et al., 2008) point to low sensitivity and high specificity, in coincidence with our own results (Table 2). Only studies involving third molars report lesser specificity, possibly due to the difficulty of correctly obtaining X-

**AUTHOR LEVEL STUDY SENSITIVITY SPECIFICITY**  Ashley 1998 enamel *in vitro* 0.19 0.80 Wenzel 1990 enamel *in vitro* 0.44 0.70 Ricketts 1997 dentin *in vitro* 0.14 0.95 Ashley 1998 dentin *in vitro* 0.24 0.89 Wenzel 1992 dentin *in vitro* 0.48 0.81 Lussi 2001 dentin *in vivo* 0.63 0.99 Heinrich 2002 dentin *in vivo* 0.70 0.96 Angnes 2005 dentin *in vivo* 0.0 - 0.06 0.98 - 0.96 Costa 2008 dentin *in vivo* 0.26 0.94 Table 2. Sensitivity and specificity values for the X-ray diagnostic evaluation of occlusal

The main difficulty of conventional X-ray exploration is the distinction between deep enamel and superficial dentin, due to superpositioning of the healthy vestibular and lingual enamel, which masks the radiotransparency, particularly in early-stage lesions. Carious lesions normally cannot be detected on X-rays until they have extended about 0.5 mm beyond the amelodentinal junction (Kidd et al., 1993). Even with this difficulty, however, *in vitro* studies point to acceptable correlation with the existing histological condition. In this context, Wenzel (Wenzel, 1998) suggested that the *in vitro* diagnostic performance may be better than in the actual clinical setting, i.e., the results obtained in the laboratory may be overestimated. However, other *in vitro* studies indicate that by the time occlusal caries have been identified on the X-rays, demineralization has already extended to the middle third of the dentinal layer, i.e., the deep dentin (Ricketts et al., 1997). Weerheijm (Weerheijm et al., 1992) reported that X-rays are not very effective for diagnosing incipient enamel caries, though the technique is very useful for diagnosing deeper lesions. In this context, conventional X-rays improve the diagnostic capacity of VI by 11%, and moreover help

assess the extent of the lesion (Ekstrand et al., 1995).

**2.4 Conventional X-rays (Rx)** 

ray projections in this zone.

caries.

Regarding the predictive value of the technique, our group (Guerrero, 2011) has recorded a PPV of 100%, suggesting that a positive diagnosis implies the existence of caries, since falsepositive interpretations are very unlikely. In turn, we recorded a NPV of 59%, i.e., normal Xray findings do not discard the possibility that an occlusal lesion may have invaded dentin. In relation to the inter-examiner reproducibility of the technique, the results are varied and range from kappa index (k) values of 0.39 (weak concordance) to 0.95 (near-perfect concordance) (Angnes et al., 2005; Costa et al., 2008; Cortes et al., 2000) – though most studies report substantial concordance values (0.61-0.80).

In sum, bitewing X-rays are an obligate diagnostic tool for proximal surface caries and represent a good adjunct in the diagnosis of occlusal caries. Considering that VI results in an important percentage of undetected clinical lesions (Wolwacz et al., 2004), particularly in adolescents (Wenzel et al., 1992), the bitewing X-rays must be carefully evaluated for possible lesions beneath the occlusal enamel. Figure 4 shows caries in dentin with a noncavitated occlusal surface. However, a normal X-ray study does not rule out the presence of hidden dentin caries, in view of the low sensitivity and NPV of the technique.

Fig. 4. Hidden dentin caries diagnosed from bitewing X-rays (A: dentin caries, B: early dentin caries)
