Different Modalities in Caries Detection and Diagnosis

Abstract

Dental caries is the most common chronic disease affecting humans worldwide. Early diagnosis of dental caries lesions allows more conservative treatment options to be followed. This may positively affect the prognosis of the condition and longevity of dental restorations. The optimum diagnosis approach should be used for better management of caries lesions. This chapter discusses several caries diagnostic modalities and systems, such as visual-tactile examination, dental radiography, transillumination-based devices, electronic caries monitors, fluorescence-based devices, and others. Furthermore, different diagnostic approaches for detecting caries lesions around different dental restorations are reviewed at the end of this chapter. Proper selection and manipulation of diagnostic tools help to enhance the outcome of dental examination. Examination should be done in clean and dry teeth for proper examination.

1. Introduction

Dental caries is a complex, noncommunicable, dynamic disease caused by biofilms. Biological, behavioral, psychological, and environmental factors all have a role in its development [1]. It has a very high incidence and prevalence throughout the world [2, 3].

The lytic effect caused by bacterial (mostly Streptococcus mutans) metabolism byproduct on enamel and exposed dentin surfaces is considered the main etiological factor that is responsible for enamel/dentin demineralization and breakdown [1, 3, 4]. Fortunately, dental caries is considered the most preventable disease that can be treated noninvasively when detected early [5]. Caries activity is a term that describes the mineral balance through time as net mineral loss (demineralization), net mineral gain (remineralization), or stability. Caries inactive indicates caries arrest or regression; caries active indicates caries initiation or progression [1].

Caries diagnosis is the clinical judgment to evaluate the existence of the disease by integrating relevant information, including the detection and assessment of caries signs and symptoms. In contrast, caries detection is the identification of these signs and symptoms. The primary purpose of caries diagnosis is to provide the greatest possible health outcome for the patient by enabling the selection of the most appropriate management and monitoring measures for the condition. This could be achieved by using valid and reliable detection tool/tools [1, 6]. Various caries diagnostic modalities and systems are discussed in this chapter, including visual-tactile examination, radiography, transillumination- and fluorescence-based devices, and others. Furthermore, at the end of this chapter, alternative diagnostic techniques for detecting secondary caries lesions are reviewed.

2. Diagnostic tool in caries detection

2.1 Visual-tactile examination

Although there are many different methods for caries detection, visual-tactile examination is considered the standard and the most used method in routine clinical examinations. It is usually combined with intraoral bitewing radiographs. The visual examination facilitated using a dental mirror and a ball-ended explorer should be performed gently on clean and dry teeth [5, 6]. International Caries Detection and Assessment System (ICDAS) and Nyvad Criteria are the most used scoring systems. They are used to clinically diagnose and evaluate caries based on a visual-tactile assessment [7].

Caries detection according to the visual-tactile examination method depends on the visual appearance and surface characteristic of the lesion [2, 5, 6]. Surface characteristics of the lesion may change according to the status of the caries activity. In the case of active caries lesions, the demineralization process progresses, and it is accompanied by rapid mineral loss. Active enamel caries typically appear whitish or yellowish with a loss of luster, and the texture feels soft when probed. It is frequently found in the pit and fissure, the gingival margin, and beneath the proximal contact points of both anterior and posterior teeth. They are usually covered with plaque. Moreover, active dentin lesions frequently appear brownish in color. The surface of the lesion feels soft, cheese-like, and fragile when probing [2].

On the other hand, when the demineralization process stops, the lesion is called arrested caries. The lesions’ appearance is affected by the interruption of mineral loss and/or mineral regain (remineralization). The surfaces of arrested enamel lesions are often whitish or brownish in color. They are smooth and feel hard on probing. While arrested, dentin lesions frequently have dark brown/black surfaces that are hard and leathery on probing. Usually, arrested lesions are not covered with plaque [2].

Visual-tactile examination is thought to be conducted and interpreted rapidly with minimal invasion and little cost aside from professional training [5]. In addition to the excellent accuracy and diagnostic performance of the visual-tactile examination in detecting caries lesions, it allows better inspection of the interested field such as the detection of the presence of plaque accumulation which may affect the treatment planning [8]. However, relying solely on visual-tactile evaluation may lead to misdiagnoses and underestimation of early caries lesions. This occurs mostly on inaccessible surfaces, such as the proximal surfaces where adjacent teeth are present [5, 6]. To overcome its limitations, different diagnostic modalities should be allocated for caries detection in addition to visual-tactile examination during examination [8].

2.2 Intraoral bitewing radiograph

Intraoral radiographs are routinely used in conjunction with visual-tactile examination to detect caries in inaccessible areas. Bitewing radiograph is the most often utilized intraoral radiograph for evaluating inaccessible surfaces [8, 9]. It has been reported that radiograph examination is more sensitive than visual-tactile examination for detecting proximal and occlusal dentin lesions, determining lesion depth, and tracking lesion behavior [6]. The usage of intraoral digital radiography technology provides the benefit of quicker examination and image manipulation than the film radiograph technique. It allows the manipulation of image characteristics (such as contrast, brightness, sharpness, and other parameters) to improve images’ clarity for better diagnosis and monitoring [5, 9].

Radiographic examination, on the other hand, has several limitations, such as exposure to ionization radiation. This might be a small but real risk, so a careful assessment of the patient’s age, caries risk, and time since the last radiographs should be weighed [5]. Furthermore, radiography cannot differentiate between active and arrested lesions and occasionally between non-cavitated and cavitated lesions [6]. The performance of the examination depends on the skill and experience of the examiner, viewing conditions, and the type of the examined object [10].

In addition, intraoral radiograph radiographic examination, in conjunction with the visual-tactile examination, provides high specificity but low sensitivity in the detection of early caries lesions [5, 11]. An intraoral radiograph can detect caries lesions with only 30–60% demineralization, so it usually underestimates the extent of the caries lesions [12]. Radiographs are used in earlier diagnoses of proximal caries compared to the visual-tactile method. However, an occlusal lesion observed on a bitewing radiograph may have progressed to the middle third of the dentine. Therefore, it is no longer considered an early lesion that could be treated with remineralization techniques. This is explained by the anatomical noise caused by the complexity of superimposed crown structures on the two-dimensional images, making it harder to detect early occlusal lesions [8, 9, 12].

2.3 Cone beam computed tomography (CBCT)

Cone beam computed tomography (CBCT) is a modified type of medical computed tomography that uses a cone-beam of radiation rather than the conventional fan beam. The main advantage of the CBCT is that it provides three-dimensional (3-D) images that allow better observation and evaluation of target tissues. Furthermore, CBCT generates images in lesser radiation doses and at a lower cost than conventional medical computed tomography [11]. Several studies were conducted to evaluate the performance of CBCT in the detection of enamel and dentin caries lesions. They concluded that CBCT could be used as a valuable tool in proximal caries detection [12, 13, 14].

Compared to intraoral radiography, CBCT showed higher sensitivity in both enamel and dentin caries detection. Since the CBCT can detect caries at a lower rate of demineralization (Figure 1) [12, 13, 14], aside from its ease of use, the CBCT produces 3D images that are free of distortion and superimposition. Also, the images could be examined in different sections and planes, which could provide additional useful information [12].

Figure 1.

Comparison of the diagnostic accuracy of CBCT and intraoral radiography for proximal caries detection. Schematic (the upper row), CBCT images (the middle row), and intraoral radiograph images (the lower row); (a) absence of proximal caries (score 0), (b) enamel caries (score 1), (c) caries extended to the outer half of dentin (score 2), and (d) caries extended to the inner half of dentin (score 3). Taken from: [12].

Nonetheless, the CBCT is not widely available, which restricts its use in routine dental examinations [13]. Furthermore, because the CBCT emits more radiation than intraoral radiography, it is not recommended for regular caries detection. It might, however, be utilized to detect caries lesions when CBCT is used for other purposes, such as preparing for dental implant placement [12, 13].

2.4 Illumination-based devices

Other approaches for detecting caries lesions include illumination-based devices. Three types of illumination-based devices use various ways of application and interpretation: optical coherence tomography (OCT), near-infrared (NIR), and fiber-optic technology (and more recently, digital fiber optics [FOTI/DIFOTI]). Each illumination-based approach employs a distinct wavelength [5]. In the following sections, a brief discussion of each type will be issued.

2.4.1 Fiber-optic transillumination (FOTI) and digital imaging fiber-optic transillumination (DIFOTI)

Fiber-optic transillumination (FOTI) is a simple noninvasive procedure that depends on illuminating the teeth – using a hand-held device – with a high-intensity narrow beam of white light. It is considered a valid and widely accepted method for proximal caries lesion detection. Based on the principle of FOTI, a dark shadow appears when the surface with disrupted enamel crystals – due to the demineralization process – is examined. This happens due to the changes in light scattering and absorption of light photons [5, 11].

Digital imaging fiber-optic transillumination (DIFOTI) is an improvement on traditional FOTI. It works on the same principle as the FOTI and employs visible light (450–700 nm) in conjunction with a camera equipped with a charge-coupled device (CCD) that may be connected to software. DIFOTI can capture real-time images of the occlusal, buccal, and lingual surfaces. Still, a subjective interpretation of the obtained images by an examiner is required. The obtained images could be used as a reference for further monitoring of the lesion [5, 10, 11].

Fiber-optic transillumination (FOTI) is widely available in dental clinics and is easy to use. FOTI – in conjunction with visual-tactile examination – may enhance the detection of enamel proximal caries in the anterior teeth and dentin proximal caries in the posterior teeth [5]. Furthermore, DIFOTI has several advantages over bitewing radiography, including the elimination of the radiation risk associated with bitewing radiography technique, real-time image viewing, reduced patient discomfort due to the absence of intraoral films or sensors, and a higher sensitivity for early caries detection [11]. DIFOTI – in conjunction with visual-tactile examinations – is suitable for the detection of non-cavitated proximal caries. Its performance improves when the probe is placed on the buccal and lingual surfaces rather than on the occlusal surface alone [15]. An in-vitro study reported greater diagnostic accuracy of DIFOTI in the detection of proximal enamel caries in premolar teeth compared to conventional film and digital radiographs. However, the diagnostic accuracies of the three methods in the detection of proximal dentin caries are comparable (Figure 2) [10].

Figure 2.

Two sets of images representing enamel proximal caries using (a) DIFOTI, and (b) digital radiograph, and dentin proximal caries using (c) DIFOTI, and (b) digital radiograph. Taken from: [10].

Digital imaging fiber-optic transillumination (DIFOTI) has not been shown to objectively quantify lesion size, depth, volume, and mineral content. DIFOTI is unable to distinguish between carious lesions and developmental defects such as fluorosis. Thus, it may give high false-positive values, potentially leading to overtreatment. Furthermore, it does not determine the status of caries activity. More in-vitro and clinical studies are required to ensure and enhance the performance, diagnostic accuracy, and reliability of FOTI/DIFOTI [5, 11].

2.4.2 Near-infrared transillumination (NIRT) and near-infrared reflection (NIRR)

Near-infrared transillumination (NIRT) devices are devices that were first introduced in 2012. They use the same principle of transillumination as FOTI and DIFOTI. However, instead of visible light, these devices illuminate the tooth with near-infrared (wavelength: 780–850 nm) light with deeper penetration through the tooth structure [5, 16, 17]. The system involves a CCD sensor to obtain the images, computer connection, software, and elastic arms containing the light source. The emitted near-infrared (NIR) light can be transmitted through the gingiva, alveolar bone, tooth root, and crown. The obtained image is revealed from the occlusal surface. Like the DIFOTI, the obtained images need interpretation by an examiner [5, 16].

NIRT devices are widely available in dental clinics and are easy to use. Examples of commercially available devices include DIAGNOcam (KaVo, Biberach, Germany) and the recently introduced iTero Element 5D (Align Technologies, San Jose USA) and TRIOS 4 (3Shape, Copenhagen, Denmark) with two intraoral scanning tools [5].

Near infra-red transillumination (NIRT) device is a noninvasive tool that permits the diagnosis of non-cavitated proximal caries lesions without the risk of ionizing radiation [17]. It showed higher sensitivity than a bitewing radiograph in detecting early enamel lesions [18]. Moreover, it has been reported that NIRT showed comparable performance in detecting lesions involving the dentin-enamel junction (DEJ) to bitewing radiographs and visual-tactile examinations [18, 19].

Even though NIRT revealed a good diagnostic performance in detecting occlusal caries lesions and identifying sound teeth, it tends to overestimate [19]. In addition, NIR has low sensitivity in the detection of early enamel caries lesions [5].

Another near-infrared-based technology is the use of near-infrared reflection (NIRR) in the diagnosis of caries lesions. Both NIRT and NIRR illuminate the tooth using a near-infrared light that is scattered by carious enamel. In the NIRR method, the scattered light results in a strong reflection of the light on the sensor. Accordingly, an increase in local light intensity at a carious lesion compared to the adjacent intact tissues makes caries appear brighter. However, caries lesions are seen in the NIRT method as dark shadows due to the scattering of light within the dentin. This makes the dentin act as a homogeneous light source that illuminates the whole enamel and dentin surfaces except for the caries lesions, which appear as dark shadows [17, 20].

It has been reported that NIRR showed comparable diagnostic performance to bitewing radiograph in the detection of enamel caries lesions. However, NIRR showed some limitations. It showed low sensitivity for proximal caries detection (Figure 3) [17, 20, 21]. In addition, teeth with opaque enamel – especially molars – makes the detection of non-cavitated proximal caries lesion impossible with NIRR [17]. It could not be used solely in the diagnosis of proximal caries lesions. Yet, more studies are still required to evaluate and enhance the efficacy of NIRT and NIRR devices in measuring the exact lesions’ depth, reliability, and validity, especially in the detection of proximal caries lesions.

Figure 3.

Premolar with non-cavitated proximal lesion that was not detectable in clinical occlusal (a) and lingual views (c). Using NIRR, a white spot was visible in the occlusal view (b) but not in the lingual view (d). Taken from: [17].

2.4.3 Optical coherence tomography (OCT)

Optical coherence tomography (OCT) is an interferometric technique that establishes cross-sectional images of biological structures without the negative effect of ionization radiation exposure. It uses coherent light with a near-infrared wavelength that has maximum depth of penetration through the biological tissues [5, 7, 22]. The first use of OCT in dental research was done by Colston et al. in 1998 [23]. In dentistry, OCT is used for many applications such as caries detection, evaluation of marginal integrity of tooth restoration, and tooth crack diagnosis [11].

Optical coherence tomography (OCT) is a noninvasive tool that creates real-time 3D images at micrometer resolution through light reflection and backscattering based on the optical absorption and scattering properties of the examined tissue [7, 11]. The OCT imaging depth is significantly impacted by the medium’s translucency. Structures that do not transmit light and deeper structures are irrelevant for OCT imaging. Sound enamel is practically transparent at the OCT wavelength range. The dentin-enamel junction (DEJ), which appears as a dark border, helps to distinguish between enamel and dentin in the OCT images. The caries tissues are shown as bright areas due to the development of multiple micro-porosities where the OCT signal’s backscatter increases [22].

Optical coherence tomography (OCT) is an industry-ready technology that is relatively easy to use and can be applied with low optical power [24]. Compared to NIRT and FOTI devices, OCT showed superior sensitivity and better performance during caries detection. It could be used as a complementary tool with conventional clinical examination methods for clearer diagnosis [5, 7].

Swept-source optical coherence tomography (SS-OCT) is a modification type of conventional OCT systems [11, 22]. SS-OCT utilizes an interferometer with a narrow linewidth, frequency-sweep laser, and detectors to determine interference versus time. The latest SS-OCT devices provide real-time cross-sectional images with microscopic-level resolution (Figure 4) [22]. SS-OCT showed higher sensitivity and specificity than bitewing radiograph in caries detection at enamel and outer one-third dentin. However, for deep caries, SS-OCT showed lower sensitivity than bitewing radiograph but with similar specificity for both methods. This was explained by the greater light scattering in dentin than in enamel [25].

Figure 4.

SS-OCT image of smooth surface enamel caries as bright zone (white arrows) in (A1, and B1), and its corresponding histological view after cross-sectioning (A2, and B2). A non-cavitated enamel lesion is seen in (A1 and A2). However, (B1 and B2) shows a cavitated enamel lesion. Taken from: [22].

On the other hand, the OCT’s primary flaw is the significant scattering of light at near-infrared wavelengths. Depending on the structure, this restricts the penetration depth from a few tens to hundreds of microns [24]. Furthermore, in the OCT images, the pulp chamber may not be clearly shown, thus preventing the determination of exact lesion extension concerning the pulp [25]. OCT is a noninvasive and safe method for the diagnosis of dental caries and is suitable for use in both pregnant women and small children [22]. The limited utilization of OCT devices in dental clinics is a result of their limited availability compared to OFTI and NIRT devices [5]. More studies are needed to evaluate the caries diagnostic accuracy of OCT and SS-OCT.

2.5 Electronic caries monitor (ECM)

The demineralization reaction has been shown to impact the electrical conductivity of the tooth. The bulk resistance of dental tissue is measured using the ECM device. Higher conductivity has been documented in caries teeth due to increased porosity within caries tooth structure and the presence of saliva within these pores. These result in a reduction of electrical resistance [5].

Electronic caries monitor (ECM) measures the electrical bulk resistance of dental tissue using a single, fixed-frequency alternating current. Both enamel and exposed dentin surfaces can be measured. A probe is used to send electricity through the tooth and body to a counter-electrode, which is typically kept in the patient’s hand. Because the body has low resistance in comparison to dental tissues, the resistance value typically closely represents that of the tooth near the probe contact point (Figure 5) [26]. It has been reported that ECM is a sensitive, practical caries diagnostic tool and has been widely used in clinical studies. Utilizing ECM offers an advantage over the sole visual-tactile examination in the diagnosis of initial caries lesions diagnosis. Therefore, it has been suggested to use it in conjunction with the visual-tactile examination during dental examination [5, 26].

Figure 5.

Electrical caries monitor. Taken from: [26].

Although ECM is claimed to be more effective than FOTI and intraoral radiography in detecting early caries lesions, it has some limitations. As a confounding factor, the presence of stains on the investigated surfaces has been shown to affect the outcome of the ECM examination. Furthermore, the reproducibility of ECM is questionable due to the possibility of probe contact site inconsistency [5]. As a result, employing ECM to identify caries lesions should be done with caution and in combination with other caries detection methods.

2.6 Fluorescence-based devices

Demineralization of the enamel tissue results in modification of the structure’s features and physical properties. Thus, If the demineralized structure is exposed to fluorescent light, it gives a different response than healthy structures. This may help in the detection and diagnosis of caries lesions. Fluorescence-based devices are classified into two categories based on the type of type of emitted light, i.e., light fluorescence, and laser fluorescence [5]. In the following sections, a brief review of each type will be discussed.

2.6.1 Light fluorescence

The qualitative light-induced fluorescence (QLF) technique can quantify small alterations in teeth based on autofluorescence, which occurs when the tooth is exposed to 405 nm visible blue light. The QLF device is composed of a light-emitted diode (LED), an inductor filter, and a metal oxide semiconductor sensor [27].

Fluorescence loss occurs because of tooth demineralization. The greater the mineral loss, the greater the loss of tooth fluorescence. Even early lesions with minor mineral changes can be detected and monitored effectively [6, 27]. When a lesion exists, an increase in light scattering causes the lesion to appear as dark patches on a bright green background. The fluorescent images of the tooth are digitalized and quantitatively assessed concerning the adjacent healthy tooth structures. A lesion is defined as any region with a reduction in fluorescence of more than 5% [6].

Qualitative light-induced fluorescence (QLF) is a noninvasive that can be used – in conjunction with the conventional visual-tactile and radiographical examination- to enhance the diagnosis of early enamel caries. It aids in the detection, quantification, and monitoring of early caries lesions that conventional methods may miss [6, 27]. Furthermore, QLF may determine both the depth and the bacterial activity of dental caries at the same time. QLF also avoids the negative consequences of radiation exposure that are linked with traditional radiographic evaluation [28].

QLF shows excellent performance and sensitivity in the detection and quantification of early smooth and occlusal caries lesions (Figure 6) [6]. In addition, Oh et al. reported a higher performance of QLF in the detection of occlusal caries lesions than the conventional methods alone but not in the detection of proximal caries. Because the intensity of light transmitted through the occlusal surface is already reflected before reaching the lesion in proximal caries, identification of the lesion is difficult if the degree of caries does not exceed a particular threshold [29]. The performance of the QLF evaluation may be affected by the presence of confounding factors such as the presence of dental plaque, staining, debris, and saliva [6, 29, 30]. Therefore, a clinician should not rely solely on QLF in the detection of caries lesions.

Figure 6.

Smooth surface caries detection using QLF technology. Taken from: [6].

2.6.2 Laser fluorescence

Laser fluorescence (LF) is a noninvasive device used to detect caries lesions and estimate their depth by exposing the tooth to a non-ionizing laser [31]. It consists of a tip that emits monochromatic red light at 655 nm wavelength and a sensor to detect the backscattered fluorescence from the examined tooth and produce a two-dimensional hyperspectral image (Figure 7) [6, 31].

Figure 7.

Laser fluorescence caries detector (DIAGNOdent TM Pen, KaVo). Taken from: https://www.kavo.com.

Carious teeth generate fluorescence proportional to the degree of caries, whereas clean and healthy teeth produce no or little fluorescence. It was proposed that these fluorescence changes are caused by protoporphyrin, a photosensitive pigment found in carious tissues as a consequence of bacterial metabolic activity [11].

Laser fluorescence (LF) has been found to tend to higher specificity than sensitivity for enamel caries detection. The performance of the LF is better with larger lesions [6]. In addition, Kapor et al. concluded that LF examination shows high sensitivity and specificity. However, it should not be used alone to avoid overtreatment [8]. In comparison to QLF, Diniz et al. reported higher sensitivity of laser fluorescence device (LF pen) in the detection of occlusal caries [32].

Several confounding factors, including the amount of plaque, calculus, and/or discoloration on the tooth surface, as well as the degree of dehydration of dental tissue, may influence the LF evaluation [6]. Thus, LF may be used as an adjunct examination method to enhance the detection of early caries lesions that could not be detected properly using visual-tactile examination alone.

2.7 Frequency-domain infrared photothermal radiometry and modulated luminescence (PTR/LUM)

Photothermal radiometry and modulated luminescence PTR/LUM technology are based on the detection of optical and thermal changes in the tooth structure [33]. PTR is based on the modulated thermal infrared response (also known as a black body or plank radiation) of a medium because of repeatedly exposing a specimen to radiation. Black body radiation is the electromagnetic energy emitted by a black body when its temperature is constant and uniform, or from a body that is in thermodynamic equilibrium with its surroundings. The sample surface’s temperature changes because of the absorbed radiation energy being transformed into thermal energy. A PTR signal-generating infrared detector can be used to measure the change in thermal emissions due to temperature modulation. LUM depends on the transformation of optical energy into radiation energy. When optical energy from a laser source is absorbed by a molecule, it causes excitement to its chromophores into a higher energy status. Then, after de-excitation to lower energy status, longer wavelength energy will be emitted. This could be detected by a photodetector that generates a LUM signal [34].

Canary caries detection system is based on PTR/LUM technology [11]. It was developed by Quantum Dental Technologies (Toronto, ON, Canada) in 2009 and used in a Health Canada-approved human investigational trial [34]. According to the manufacturer, the Canary caries detection system (Figure 8) can detect caries from 50 to 5 mm depth including secondary caries detection around sealant and restorations’ margins. Canary caries detection system values are not affected by stains and the presence of calculus or saliva [11].

Figure 8.

The canary system from quantum dental technologies. Taken from: https://www.dentalcompare.com.

An in-vitro study compared the performance of the Canary caries detection system in the detection of proximal caries lesions to the performance of visual-tactile and radiographical examinations. They used polarized light microscopy as a gold standard in caries detection. A higher sensitivity of the PTR/LUM caries detection system compared to the other two examinations tested was reported. There was no significant difference in specificity between the radiographical examination and the PTR/LUM method. In contrast, the specificity of the visual-tactile examination was the lowest among the three examination methods [33]. In addition, a study by Xing et al., in 2023, reported a positive moderate correlation with the caries depth of the PTR/LUM system; even a 20° deviation from perpendicular did not affect its performance [35]. Also, it has been reported that the PTR/LUM system can detect non-cavitied proximal lesions without the use of ionization radiation [36]. However, the PTR/LUM caries detection method is still considered new, and more in-vitro and clinical studies are required to evaluate its performance and accuracy.

2.8 Ultrasound

The first use of ultrasound in dentistry was by Baum et al. in 1963 [37]. Sound waves with frequencies (20 kHz) higher than those heard by humans are used in ultrasound technology. During caries detection, ultrasound depends on the substantial variations in sonic conductivity between sound and demineralized dental structures. The use of ultrasound to detect caries is considered simple, safe, and provides real-time images, among other benefits [11]. A recent study reported a high correlation between histological and ultrasound examinations’ results in the detection of smooth surface enamel caries [38].

Although it showed promising performance in caries detection, there are only limited studies done to evaluate the efficacy of the ultrasound system for caries detection.

3. Detection of secondary caries lesions

Secondary caries (also known as recurrent caries) are caries lesions that form near the margin of a restoration. Other examination approaches besides the visual-tactile assessment could improve the longevity of the restoration. Secondary caries could be predicted by the presence of marginal ditching, discoloration of adjacent tooth structures, and gaps at the tooth-restoration interface. Unfortunately, these signs are not reliable predictors making the detection of secondary caries lesions with solely visual examination challenging. Alternatively, relying solely on radiographic evaluation may result in an underestimate of lesion extent. The radiopacity of restorative materials may contribute to secondary caries misdiagnosis [39].

Several studies suggested the use of LF along with visual-tactile and radiographical examinations for the detection of secondary lesions [40, 41]. While NIR transillumination appears to be promising in the detection of secondary caries, there is little data to support it. Even though just a few studies have been conducted to evaluate the use of visual-tactile evaluation with QLF, this method has demonstrated poor performance [40].

While CBCT images detect proximal caries more correctly than bitewing radiography, the presence of high-density restorative materials such as dental amalgam and porcelain restorations results in metal artifacts. This lowers the CBCT’s accuracy in detecting secondary caries lesions. Because of its atomic number and density, amalgam restoration produces more artifacts than porcelain and metal-ceramic restoration. As a result, there are more false-positive results [12]. However, other studies showed higher diagnostic accuracy of CBCT compared to bitewing radiography in the detection of secondary caries around resin composite restorations [14, 42].

Optical coherence tomography (OCT) has also been investigated for the detection of secondary caries. The presence of opaque and metallic restoration makes subsequent caries detection with OCT challenging (Figure 9). However, the satisfactory performance of the OCT in detecting secondary caries around tooth-colored restorations that can transmit light has been documented [22]. In addition, the detection of secondary caries around tooth-colored restorations could be established by the PTR/LUM system. Abrams et al. reported that the PTR/LUM system (The Canary System, CS) has the potential for more accurate diagnosis of secondary caries around compomer and resin-modified glass ionomer restorations than visual-tactile examination, light-emitting diodes fluorescence, and LF used [43].

Figure 9.

SS-OCT is not able to detect caries lesion underneath the metal alloy in the first molar. SS-OCT image of proximal contacts between second premolar and first molar (scanning from occlusal surface). A distinct white line indicates the presence of caries (arrow). Cross-sectional imaging of the first molar is not possible due to the metal inlay (right). The presence of dentin caries in the mesial and distal proximal surfaces of the second premolar is confirmed after cavity preparation (left). Taken from: [22].

Based on the exceeding, adjunctive diagnostic aids – in addition to conventional visual-tactile and radiographic examinations – should be used when detecting secondary caries lesions to improve diagnostic outcomes and avoid overtreatment. This is particularly applied when examining teeth with high-opacity restorations. Restorations’ finishing may be required to overcome the limits of some diagnostic aids that are influenced by the presence of staining.

4. Conclusion

In conclusion, the most common and widely used approach for caries detection and assessment is a visual-tactile examination combined with a radiographic examination. It does, however, have certain limits. As a result, various diagnostic tools and modalities are available and might be employed to improve caries diagnosis accuracy and sensitivity. A proper caries detection method should be carefully selected and implemented on clean and dry surfaces. More laboratory and clinical research is required to assess and improve the performance of such methods.

Conflict of interest

The author declares no conflict of interest.