1. Nishtar Medical University, Primary & Secondary Healthcare Department, Pakistan; hpereformer@gmail.com
2. Bilal Hospital, Rawalpindi, Pakistan; aghasajid51@gmail.com
3. Oral & Maxillofacial Surgery Department, King Edward Medical University, Lahore, Pakistan; nabeelariaz@yahoo.com
4. King Edward Medical University, Mayo Hospital, Lahore, Pakistan; rabiazulfiqar77@gmail.com

*                 Correspondence: hpereformer@gmail.com

Keywords: technology, early caries, diagnostic tools

1. INTRODUCTION

Tooth decay, also referred to as dental caries, is one of the most frequent chronic disorders [1]. It is the progressive loss of tooth substance brought on by a complicated interplay between fermentable carbohydrates and cariogenic bacteria found in dental plaque biofilm. This interaction causes bacterial acid assault and upsets the delicate balance between the demineralization and remineralization of dental hard tissue [2, 3]. According to a study by the Global Burden of Disease Collaborative Network, 532 million children worldwide have untreated primary tooth caries, and 2.4 billion people worldwide have untreated caries on permanent teeth [4]. The high global frequency of caries may be attributed, in part, to early caries that go undetected and later deepen into carious lesions [5]. The medical model that underpins the contemporary caries management philosophy emphasizes minimally invasive surgical treatment, non-restorative therapy, and caries prevention [6]. Early treatments can preserve good dental hard tissue when dental caries is detected, especially in its early stages. Consequently, dental caries must be prevented and managed, and early diagnosis and evaluation of dental caries are crucial [5,7]. The visual-tactile technique is the most widely used and accepted way to identify early caries [8]. This method entails utilizing a dental explorer to detect the texture change of hard tissue lesions and the visual colour change of the teeth [9]. This method is easy to use and inexpensive, but a review found that it is not ideal for early diagnosis of caries since it has poor sensitivity and relatively high specificity [10]. Moreover, visual inspection is not practical for locations where direct visualization is not possible. Additionally, a study found that the use of dental explorers in caries inspections can worsen the development of the carious lesion and further harm demineralized enamel structures [11]. The need for innovative caries detection techniques has arisen as a result of the shortcomings of traditional methods. Many technologies have been created, especially cutting-edge digital diagnostic tools that can spot lesions early on. Digital aids are tools that use digital data to diagnose dental caries and are getting more and more common across a range of professions. Thus, the purpose of this review is to present a summary of digital diagnostic tools for the clinical identification of early dental caries.

2. MATERIALS AND METHODS

Using the terms “(early caries) OR “beginning caries)” AND “(digital) OR “light” OR “laser” OR “fluorescence) OR “trans-illumination)” AND “(Detection) OR “Assessment”), a thorough literature search was conducted on the PubMed, Scopus, and Web of Science databases. Following a preliminary search of publications pertaining to computerised diagnostic tools for dental caries, the keywords were selected. It was discovered that a number of keywords, such as “light,” “laser,” “fluorescence,” and “trans-illumination,” appeared often in the majority of papers. Since early caries, or beginning lesions, are the hardest to identify, we have also included research that focus on them. In these cases, digital aids might be especially helpful. Selected and retrieved studies were those that were published on or before December 31, 2022. With 577 papers in Pubmed, 481 publications in Web of Science, and 608 publications in Scopus, a total of 1666 results were obtained. 650 publications were left after duplicates were eliminated so they could be evaluated further. Digital diagnostic aids for the detection and assessment of dental caries were included in the screening process of study titles and abstracts (Figure 1). Articles that had nothing to do with dental caries in humans were judged irrelevant. These digital diagnostic tools fall into several categories based on the energy sources they use. A variety of energy sources, such as visible light, lasers, coherence lights, ultrasound, electricity, and X-rays, can be used as digital signals to help identify dental cavities. These digital diagnostic aids for dental caries detection are classified as radiation-based, light-based, ultrasound-based, and electric-based depending on the energy source they use (Figure 2). Images for caries detection are provided by light- and radiation-based diagnostic tools. Figure 2 therefore displays sample photos of radiation- and light-based diagnostic tools for the identification of dental caries. When caries is detected, digital signals are frequently converted into numbers or spectrums using ultrasound- and electric-based diagnostic tools.

Figure 1: PRISMA Flow Chart

3. DIGITAL DIAGNOSTIC AIDS FOR CLINICAL USE

3.1. Radiation-Based Diagnostic Aids

The 1890s saw the introduction of the X-ray, a type of electromagnetic radiation with particular wavelengths between 10 nm and 0.01 pm, which was used to detect dental cavities [12]. Because digital radiography is easier to use, produces better images, and has higher diagnostic accuracy than conventional radiography, it has steadily displaced the latter over time [13]. According to a review, digital radiography is more accurate than traditional analogue radiography [14]. Cone beam computed tomography and digital bitewing radiography are examples of radiation-based diagnostic tools that are employed in clinical settings. When X-rays interact with the film’s emulsion, digital bitewing radiography employs photographic film or digital detectors to record pictures [12]. After a clinical assessment of dental caries for approximal caries, occlusal caries, or secondary caries, digital bitewing radiographs are frequently used [15]. Through the long-term monitoring of carious lesions and the observation of lesion extension or changes in dentine or enamel density over time, this technology offers a qualitative diagnosis [14, 16]. However, it’s important to recognise some limitations. First off, worries about elevated radiation danger have prompted discussion on the regular use of intraoral radiography, particularly for those with low caries risk [17]. Furthermore, because the radiographic lesion depth does not always reflect the real caries lesion, such radiographs are unable to distinguish between active and halted carious lesions, as well as occasionally between cavitated and non-cavitated surfaces [18]. Another thing to keep in mind is that radiographs can only show lesions in the enamel that are at least 500 µm deep. Its clinical utility is limited by the incapacity to identify early carious lesions [19]. Clinical trials on permanent teeth have revealed wide variations in the accuracy of digital bitewing radiography. When it comes to detecting occlusal caries, bitewing radiographs have a sensitivity of 0-0.93 [5, 20, 21] and a specificity of 0.6-1 [5, 20, 21]. The sensitivity and specificity values for the detection of approximate caries are 0.15–0.83 [5,22] and 0.6–0.99 [5,22], in that order. Dental cone beam-computed tomography (CBCT) creates three-dimensional, high-resolution pictures in the frontal, sagittal, and axial planes by using an X-ray beam that is shaped like a cone or pyramid and detectors that are primarily flat panels [23]. CBCT produces three-dimensional pictures, which can be used to diagnose cavities in any place of a tooth. This method’s primary advantage is its ability to get over the drawbacks of two-dimensional imaging [24]. However, utilising CBCT as a radiographic modality has been associated with certain limitations, including radiation dose, expenses, and image artefacts [17]. There is a great deal of variation in the literature on the accuracy of CBCT in identifying dental caries. When compared to bitewing radiography, multiple in vitro investigations shown that CBCT did not offer a higher diagnostic accuracy for identifying dentine and enamel cavities [25, 26, 27]. However, a different study found that CBCT outperforms intraoral radiography in terms of sensitivity in identifying cavitated approximal carious lesions [28]. CBCT has been shown to have a stated sensitivity of 0.75–0.79 and specificity of 0.77 in approximal lesions for clinical studies in permanent dentition [28]. Generally speaking, regular caries detection does not recommend using CBCT as the primary diagnostic method.

3.2. Light-Based Diagnostic Aids

Light-based diagnostic tools produce signals using different kinds of light or lasers and look for variations in those signals in teeth that are carious. These days, there are three main types of light-based diagnostic tools: light-induced fluorescence, laser-induced fluorescence, and digital transillumination. Transillumination is a method of passing light through bodily tissues and using the light’s intensity to determine the tissue’s density and makeup [29]. Higher porosity fibrous tissue absorbs more light and appears darker when illuminated by transillumination [30]. Conventional fiber-optic transillumination only enables the immediate on-site evaluation of the examination result; it is unable to make images. Digitalization has been integrated into transillumination in order to address this problem. Invisible near-infrared light with an oscillation wavelength of 700–1500 nm is the most often used light source for digital transillumination [31]. Compared to visible white light in conventional transillumination, this light can penetrate deeper into dental tissues because of its decreased dispersion and absorption, which improves the contrast between healthy and carious tissues [32]. When approximating caries is detected, digital transillumination is particularly helpful [33]. Compared to visual inspection and radiography, digital transillumination has the advantages of a lower radiation dose, less discomfort for the patient, real-time image viewing, and overall higher feasibility [33, 34, 35]. Nevertheless, the size, volume, mineral content, and caries activity of a lesion cannot be precisely determined by digital transillumination. Over diagnosis and overtreatment may result from its inability to differentiate between developmental abnormalities like fluorosis and carious lesions [36]. Furthermore, caries identification may be hampered by the challenges associated with obtaining high-quality pictures [34]. Proximal caries was the subject of the majority of research on digital transillumination’s accuracy. In clinical trials, digital transillumination demonstrated sensitivity at 0.44–0.991 and specificity at 0.61–0.941 for the detection of proximal caries [31, 37]. Fluorescence has been induced in caries lesions using a range of wavelengths of light, including ultraviolet light (100–400 nm), the visible light’s green–yellow end (370 nm), the visible light’s blue–violet end (400–450 nm), and near-infrared light (750–10,000 nm) [38,39,40]. One kind of luminescence is fluorescence, which is the longer wavelength light that a substance emits after absorbing low wavelength light or other electromagnetic radiation [41]. Based on the observation that carious lesions differ in their fluorescence characteristics from healthy tooth tissues, fluorescence is used in caries detection. The occlusal surface, the buccal/lingual surface, and the proximal surface with a sufficient interproximal space are among the surfaces of the carious tooth that can be treated with light-induced fluorescence. By measuring the average fluorescence loss in carious tooth tissues relative to healthy enamel and translating that loss into mineral density, it makes it possible to quantify the amount of mineral loss in the caries lesion [42-44]. In comparison to radiography and visual examination, it also offers the advantages of a lower radiation dose, less discomfort for the patient, and real-time image viewing and storage. It cannot, however, be used in areas where light cannot directly reach, like the tooth’s proximal surface when a neighbouring tooth is visible. Furthermore, the interpretation of the detecting data should be cautious to prevent overdiagnosis since light could trigger the creation of fluorescence from subjects other than carious teeth in the oral cavity [45]. The majority of clinical research on light-induced fluorescence’s diagnostic accuracy is based on equipment that uses visible light in the blue-violet (400–450 nm) end of the spectrum. The sites for detection affect how accurate diagnostic tools that use blue-violet light-induced fluorescence are. According to reports, the occlusal caries sensitivity and specificity were 0.26–0.92 and 0.41–0.1, respectively [5,21,46]. The sensitivity and specificity ratings for the identification of approximate dental caries were 0.74 and 0.73, respectively [21]. Sensitivity and specificity for buccal caries were reported to be 0.49–0.80 and 0.74–0.85, respectively [5]. Using a red-light laser with a wavelength longer than 655 nm, laser-induced fluorescence stimulates fluorescence in carious tissues [43]. Light amplification through stimulated emission of radiation is referred to as laser. It is an electromagnetic wave generator that concentrates light into a narrow beam and generates a single wavelength of light [47, 48]. To help with caries diagnosis, the laser can produce fluorescence from protoporphyrin, a photosensitive pigment produced by bacterial metabolic activity in carious lesions [49]. The intensity of the fluorescence released is correlated with the severity of caries since healthy tooth tissues either produce little or no fluorescence [49]. Carious lesions can be identified using laser-induced fluorescence on the occlusal, smooth, and proximal surfaces of the tooth. It may calculate the depth of the carious lesion and show a number between 0 and 99, where larger scores suggest the need for restorative treatment and lower scores indicate healthy tissues [50, 51]. When compared to visual inspection and radiography, it offers the same benefits as light-induced fluorescence, such as a lower radiation dose, less discomfort for the patient, and real-time chairside detection. When compared to light-induced fluorescence devices, patient communication may be more challenging with the current generation of laser-induced fluorescence devices since they show the results using numerical data. Additionally, there is a chance that laser-induced fluorescence will produce false-positive results, which could result in overdiagnosis [45]. Laser fluorescence was shown to have a sensitivity value of 0.48–1 and a specificity value of 0.2–1 in earlier research [5,46,52,53]. False-positive diagnoses are also a possibility, which could result in overtreatment. Consequently, it is advised that laser fluorescence be utilised as an additional diagnostic tool rather than the main diagnostic instrument for the identification of dental caries.

3.3. Electric-Based Diagnostic Aids

Emile Magitot first suggested using electricity to diagnose dental cavities in 1878 [54]. The high electrical resistivity of hydroxyapatite, the primary ingredient in dental enamel, is the basis for the operation of electric-based caries detection instruments. When dental caries develops, the porosities in the hard tissue of the teeth get larger and hold more oral cavity fluids that conduct electricity than they do in healthy teeth. This ionic fluid fills the porosities, resulting in an increase in electrical conductance and a decrease in electrical resistance [55, 56]. Depending on the electric current’s frequency, two types of electric-based methods for diagnosing caries can be distinguished: electrical conductance measurement and alternating current impedance spectroscopy. A carious tooth’s electrical conductance is measured by an electrical conductance measurement equipment using a single, fixed-frequency alternating current [55]. In order to complete the circuit, the measuring electrode is made to fit into deep pits and fissures and come into contact with a tiny amount of dentinal fluid [57]. A circuit of the current flow cannot be completed on a tooth with unbroken enamel and no carious lesions, hence the gadget reads zero. A lesion would result in a current flow and a closed circuit, which would give the gadget a reading [57]. On occlusal, proximal, and smooth surfaces, the electrical conductivity measurement tool enables the identification of caries lesions that are both cavitated and non-cavitated. Electrical conductance measurement allows for a quantitative assessment of caries severity because the reading is correlated with increased porosities and mineral loss. Additionally, this diagnostic tool can distinguish between stains and cavities, which may be detected by optical and fluorescence approaches [57]. The cost and viability of such technologies are still hot topics of debate, though. There is little research being done on measuring electrical conductance [58]. An electrical conductance testing tool revealed a high sensitivity value of 1 and a specificity value of 0.93 in detecting early occlusal caries, according to an in vitro investigation [57]. With alternating current impedance spectroscopy, the teeth’s impedance, or resistance, to alternating current, is measured. With the use of several electrical frequencies, this detection technique generates a spectrum of data that offers additional details on the chemical and physical characteristics of a tooth [55]. The possibility of caries can be indicated by moving a sensing brush over the suspected carious location, which will provide a numerical readout along with a colour code [59]. Early detection of carious lesions is possible with this technique. The clinical sensitivity and specificity for identifying occlusal caries in permanent teeth were found to be 0.75–0.97 and 0.3–0.92, respectively, according to a systematic review and meta-analysis [5].

3.4. Ultrasound-Based Diagnostic Aids

By using longitudinal ultrasonic waves’ sonic conductivity to distinguish between sound and demineralized hard tissue, ultrasound has been used in dentistry as a diagnostic tool for caries identification. It makes use of ultrasonic waves, which are able to travel across hard tissue surfaces that are curved, smooth, or flat. A prototype ultrasonic caries detector has been built using ultrasound-based diagnostic tools. To find caries lesions, especially approximate carious lesions, the ultrasonic probe of the ultrasonic caries detector can be positioned at a specific angle [60,61]. Because the ultrasonic waves are amplified and substantially larger than the background level, making wave profiles easier to understand, ultrasonic caries detectors are comparatively simple [60]. Furthermore, it is not necessary to apply the ultrasonic probe directly to caries lesions [60], expanding its clinical applicability to caries lesions that are challenging to evaluate. This technique has the potential to be a caries diagnostic aid due to its advantages of good directionality, high penetration level, and non-toxicity [62]. However, it has been noted that ultrasound has a limited spatial resolution in the medical industry, making it less competitive [63]. Another disadvantage of this digital detection device is its inability to determine the depth of carious lesions [60].

4. DIGITAL DIAGNOSTIC AIDS UNDER DEVELOPMENT

While there are a number of digital diagnostic tools available, not all of them are universally applicable and have varying degrees of limitation. Furthermore, none of them have demonstrated optimal effectiveness in identifying dental caries, particularly when it comes to early-stage caries. As a result, numerous cutting-edge digital diagnostic tools for dental caries are being developed. Although none of the following digital diagnostic tools are yet commercially available, they have the potential to be used in clinical settings.

4.1. Optical Coherence Tomography

Depending on the optical absorption and scattering characteristics of the tissue, optical coherence tomography (OCT) generates two- or three-dimensional pictures [70]. The concept of interferometry, which produces light wave interference patterns by the interaction of an emitting light and backscattered light from a sample, is the foundation upon which the images are constructed [71]. To create a micro-structure profile of biological tissues, the interference patterns are compared to the pattern produced by a reference light [72]. For the detection of caries, swept-source (SS-)OCT can be employed. When compared to conventional OCT systems, it offers higher sensitivity, faster imaging, and higher picture resolution [71]. The illuminating output is usually a near-infrared laser with a centre wavelength of about 1310 nm [72]. Demineralized enamel or dentine appears as a bright zone in SS-OCT pictures of caries detection because carious tooth structure increases backscatter signal [72]. Clinical applications may benefit from SS-OCT’s ability to deliver real-time video-rate imaging with an enhanced acquired picture signal-to-noise ratio [72]. For caries at all severity levels, an in vitro investigation revealed that SS-OCT had a greater sensitivity than eye assessment [72]. An in vivo investigation verified that SS-OCT is more accurate and dependable in detecting proximal caries than bitewing radiography [71]. While there is currently little in vivo research on OCT, OCT system advancements open the door to more non-invasive tools for digital caries diagnosis. But as of yet, this technique is not ready to be used as a paid clinical caries detection tool [73].

4.2. Laser-Related Caries Detection

Lasers can be used to create signals other than fluorescence in order to identify dental cavities. To help in caries diagnosis, a laser can provide various signals on the tooth surface, such as thermal, acoustic, photonic, etc. The foundation of thermal imaging technology is the idea that a carious lesion’s degree of porosity influences the quantity of water retained in the tooth and, consequently, its temporal profile [74]. The temporal profile is associated with the ongoing evaporation of water from dental tissues’ porosities, which causes thermodynamic changes on the tooth surface until the tooth dries up and a new equilibrium is formed [74]. Thermal imaging technology operates by sensing the temporal profile of the tooth immediately after exposure to a heat pulse or by recording the temporal profile of the chronological evaporation of a carious tooth surface as it dries [74]. Modulated thermal infrared response, sometimes referred to as black body or Plank radiation, is a byproduct of repeatedly irradiating a material and is used in photothermal radiation (PTR). When a specimen is in thermodynamic equilibrium with its surroundings, the thermal electromagnetic radiation inside or around it is what is known as emitting black body or Plank radiation. Its intensity and particular constant are entirely dependent on the specimen’s temperature. The energy from the radiation is absorbed by the specimen and transformed into thermal energy, which is manifested as a shift in surface temperature. The PTR signal can be used to measure this energy conversion with an infrared detector [75]. Modulated luminescence technology (LUM), which detects the wavelength released when absorbed optical energy from a laser source is transformed into radiation energy, is combined with PTR in recent caries detection technologies. A photodetector with a LUM signal can be used to find this [75]. Pit and fissure caries can be found up to 5 mm below the surface of a tooth using frequency-domain laser infrared photothermal radiometry and modulated luminescence technology (FD-PTR/LUM). This technique can distinguish between lesions on the outer half of the enamel or healthy dental surfaces and lesions that extend to the middle or deeper into the enamel, according to an in vitro research [48]. Additionally, studies showed that FD-PTR/LUM had higher sensitivity and specificity values than radiography, ocular inspection, and laser fluorescence methods in identifying early occlusal caries [76]. The specificity value for FD-PTR/LUM is comparable to radiography but much greater than visual inspection for approximate caries identification [76]. The sensitivity value is higher than both radiography and visual examination. Nonetheless, the temperature readings of FD-PTR/LUM can be affected by variations in the humidity and temperature of the oral cavity [48]. Laser-induced breakdown spectroscopy (LIBS) using a yttrium aluminium garnet (Nd: YAG) laser doped with neodymium can be used to identify caries. With this method, the spectrum variations of the element contents in a tooth sample—typically enamel—are analysed. Enamel is made up of non-matrix elements including carbon, magnesium, zinc, and potassium as well as matrix elements like calcium and phosphorus in the form of hydroxyapatite [77]. Every component of the tooth has a wavelength that it absorbs specifically. Whether a tooth is healthy or carious can be determined by observing changes in the components’ relative concentrations. For instance, the sample is carious if there is a decline in matrix elements and a rise in non-matrix elements [77]. With the use of this technology, a dentist would be able to track changes in tooth structure in real-time and in vivo as a result of caries and plaque removal [77]. Dental caries can be diagnosed by assessing the characteristics and thickness of dental hard tissue using laser-induced acoustic spectroscopy. When a pulse laser is used to irradiate a tooth, the laser energy is absorbed and causes localised temperature rise and thermal expansion, which in turn excites sonic waves [62]. Acoustic wave time and frequency domains alternate in a decaying tooth. When a laser beam is applied to dental tissues, a surface acoustic wave known as a Rayleigh wave is created [61]. A carious lesion’s form, depth, and degree of demineralization can all be determined from the Rayleigh waves’ velocity field [62]. This device has employed both Nd:YAG and carbon dioxide pulse lasers to stimulate the acoustic waves of a tooth that has deteriorated. The principal use of this diagnostic technique is to detect early carious lesions, in which the mineral composition has not altered. Using a laser beam light source with a specific wavelength in the visible and infrared light spectrum, an in vitro investigation investigated the existence of both advanced and incipient caries [61,78]. Acoustic imaging’s primary benefits are its improved spatial resolution and deeper penetration depth [79]. To make photo-acoustic imaging a useful clinical tool for operators, more research is required.

4.3. Diagnostic Interpretation Aids

New approaches have also been created to improve the precision with which the outcomes of computerised diagnostic tools are interpreted. Based on the computerized diagnostic aids’ caries-detecting results, these diagnostic interpretation tools were used. For instance, automated exposure compensation (AEC) is an additional digital tool that may be used with digital intraoral radiographs to enhance image quality and diagnosis accuracy [80, 81]. By lowering the possibility of human assessment errors, artificial intelligence has been used to increase the precision, consistency, and effectiveness of digital diagnostic tools [82].

5. CONCLUSION

Dental caries detection tools that use digital diagnostics have been developing. As digital diagnostic tools for dental caries identification, radiation-based, light-based, ultrasound-based, and electric-based aids are now available. There are benefits and certain limitations to these computerized diagnostic tools that are now on the market. By serving as adjunct methods to traditional caries detection, they help physicians identify dental caries. But none of them have demonstrated perfect performance in identifying dental caries, particularly when it comes to early-stage caries. As a result, several cutting-edge computerized diagnostic tools for dental caries are being developed and have the potential to be used in clinical settings. Additionally, the goal of this study is to provide doctors with a more thorough evaluation of the digital diagnostic tools that are now on the market. It also acknowledges and contrasts the many modern technologies that are listed in order to make it simpler to diagnose dental caries early on and prevent it from progressing.

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