Advanced diagnostic aids in dental caries – A review

INTRODUCTION

Dental caries is a complex disease, defined as a progressive, irreversible, microbial disease affecting the hard parts of the tooth exposed to the oral environment, characterized by demineralization of inorganic constituents and destruction of the organic constituents thereby leading to a cavity formation.^[1] As long as the dynamic equilibrium between the mineral content of the tooth-oral fluid and the microbial content of the biofilm are maintained, the entire sequence remains within the boundary of a physiological process, where loss and gain are equalized.^[2] However, if the factor disturbing this homeostasis is strong, intense, and long lasting, then the demineralization persists and prevails. The mineral loss is now more than the gain, which becomes evident as structural changes in the tooth structure. Along a timeline, this shift in the balance leads to more changes in the tooth structure, which cannot be accepted as healthy, but should be considered as pathological. Thus, the physiological dental caries process becomes a pathological dental caries disease.^[3]

The change of dental caries from a physiological process to pathology is a continuous process and is affected by numerous variables and also there is a lack of a specific boundary line between health and disease. The progression of non cavitated lesions seems to be slower, allowing preventive strategies to be implemented when the lesions have the greatest opportunity to arrest.^[4] Thus, early and accurate detection and diagnosis of dental caries are an important component of the overall management of dental patient. It is imperative that the diagnostic methods with suitable level of sensitivity and specificity are used in conjunction to obtain a valid diagnosis. This paper aims to review some of the advanced caries diagnostic methods available.

ILLUMINATION METHODS

1. Fiber-optic transillumination (FOTI)

2. Wavelength dependent FOTI

3. Digital imaging FOTI (DIFOTI).

FOTI

In recent years, because of concerns over the cumulative effects of ionizing radiation, a simple technique called FOTI that utilizes a light emitting diode was developed for caries detection, which uses a narrow beam of white light to transilluminate the tooth. FOTI, as a caries detector technique, is based on the fact that carious enamel has a lower index of light transmission than sound enamel. As the demineralization process disrupts the crystalline structure of enamel and dentin, more light is absorbed due to changes in the light scattering and absorption of light photons. In essence this gives that area a more darkened appearance.^[5]

FOTI was initially designed by Friedman and Marcus in 1970 for the detection of proximal caries. Posterior approximal caries is diagnosed by placing the light probe on the gingiva below the cervical margin of the tooth, whereby light passes through the tooth structures and approximal decay appears as dark shadow on the occlusal surface. The FOTI has higher sensitivity for dentin lesions than for enamel lesions.

Meta-analysis by Ie and Verdonschot^[6] showed that FOTI performed superiorly in diagnosing occlusal caries in comparison to visual inspection and xeroradiography and a study by Ismail^[7] observed that FOTI is the most valid method for caries detection of precavitated caries in dentin followed by radiographic examination and visual examination. Peers et al.^[8] carried out an in vitro comparison of the performance of radiography and FOTI using histologic examination as the gold standard. They found no significant differences in the Sn values of radiography (0.59) and FOTI (0.67) with regard to approximal caries detection. FOTI is widely accepted by clinicians as a valid method for detection of approximal caries in anterior teeth as well as dentin- involved caries in posterior teeth.

In reference to occlusal caries, Wenzel et al.^[9] consider transillumination to offer better performance than conventional X-rays in detecting early-stage dentin caries. Côrtes et al.,^[10] in an in vitro study, reported greater sensitivity than specificity for FOTI and superior performance with respect to X-rays both for enamel and dentinal lesions and had a better correlation with histology.

However, the fact that FOTI is not routinely used by dental professionals and is not recommended as a technique of choice, due to a large proportion of false-negative results. The main advantage of FOTI is its optimum positive predictive value performance, which means that any positive reading is almost certainly indicative of an existing lesion, no exposure to radiation, gives instant images simple, non time consuming, and comfortable to patients.

DIFOTI

This technique was introduced to overcome the limitations of FOTI by combining FOTI and a digital charge-coupled device (CCD) camera. DIFOTI is the only dental diagnostic imaging instrument of its kind to be approved for the detection of incipient, frank, and recurrent caries.^[15] It can also be used to detect fractures, cracks, and secondary caries around restorations.

It is based on the principle that carious tooth tissue absorbs more light than surrounding healthy tissue and appears as darker area. DIFOTI system consists of two handpieces (one for occlusal surface and one for smooth surface and interproximal areas), a disposable mouthpiece, a foot pedal for selecting the image of interest and a computer system to capture and store the resulting image.

Schneiderman et al.^[16] found that DIFOTI technique has superior sensitivity over conventional radiographic methods for the detection of approximal, occlusal, and smooth surface caries. Hae-Woong et al.^[17] observed that the DIFOTI diagnostic system is the most accurate means of detecting occlusal, buccal, and lingual surface carious lesions, while mesial and distal proximal carious lesions were most accurately assessed using bitewing radiography.

Kazuhiro^[18] examined the clinical usefulness of DIFOTI, to detect dental caries and cracks. Image data of the tooth obtained by visible-light fiber-optic transillumination were acquired with a digital CCD camera and sent to a computer for image analysis. Then, the incorporated data are immediately projected on the monitor as an image of the tooth. As a result, DIFOTI was shown to be effective in detecting initial caries and cracks on the surface of a tooth.

Bin-Shuwaish et al.^[19] evaluated the correlation between DIFOTI and clinical and radiographic images in estimating the true clinical axial extension of Class II carious lesions. It was observed that DIFOTI images correlated well with clinical depth, especially for smaller lesion. It also improved the estimation of lesion size when used in conjunction with the digital sensor and D-speed images. As reported by Astvaldottir,^[20] though the potential for detecting lesions in dentin by DIFOTI, Film and digital radiography is similar, the diagnostic accuracy of DIFOTI in detecting early approximal enamel lesions was greater 20.

Although it has certain advantages like gives instant images that can be stored for future references, there are several limitations of DIFOTI. The method does not measure lesion depth, and a difficulty in discriminating deep fissures, stain, and actual dentin lesions. Furthermore, overdiagnosis can occur due to lower specificity when compared with conventional radiographs. Dark areas on the images can be attributed to scatter and the absorption of light as it passes through demineralized enamel and dentin or near the surface; consequently, white spots can be mistaken for cavitations.^[21]

MIDWEST CARIES ID™ (MID)

MID is a small, battery-operated technology that emits a soft LED light for detecting and quantifying caries. A specific fiber optic signature captures the resulting reflection and refraction of the light in the tooth and is converted to electrical signals that run through a computer-based algorithm for analyzing the presence of caries.

Patel et al.^[22] reported the sensitivity and specificity for this detection device as 0.56 and 0.84, respectively. Krause et al.^[23] reported sensitivity of 100%, which was calculated by comparing the Midwest to radiographic findings. However, Rodrigues et al.^[24] assessed the performance of two LED (MID and Vista Proof-VP) and two laser fluorescence (LF)- based devices (DIAGNOdent 2095-LF and DIAGNOdent pen 2190-LF pen) in detecting occlusal caries in vitro on 97 permanent molars. Both LF devices seem to be useful as supplementary tools to conventional methods, presenting good reproducibility and better accuracy. Furthermore, MID could not differentiate sound surfaces from enamel caries and VP still needs perfection on the cutoff limits for its use.

Aktan et al.^[25] compared laser-based (DIAGNOdent) and LED-based (MID) in the detection of occlusal caries and concluded that MID device more regularly revealed the presence of occlusal caries in comparison to DIAGNOdent pen. Van Hilsen and Jones^[26] evaluated and compared MID, visual photographic examination (CAM) and cross- polarization optical coherence tomography (CP-OCT) observed that MID and CP-OCT were useful in detecting the presence of demineralization, but cannot be utilized to adequately assess the depth of the demineralization.

ENDOSCOPY

Endoscopy includes:

• Endoscopically viewed filtered fluorescence

• White light fluorescence

• Videoscope.

INTRAORAL TELEVISION CAMERA (IOTV)

Intraoral cameras are based on the same idea as endoscopes, using a small visualization device to provide a better view of the oral cavity. The intraoral wand camera projects magnified digital images from a patient’s mouth. Through the IOTV, the dentist can educate the patient and at the same time, can also improve their own diagnostic expertise as they see magnified oral conditions which are significantly better than direct vision.

Certain advantages such as increased vision, improved posture, and patient positioning, and increased magnification helps in diagnosis. Forgie et al.^[29] concluded that IOVC can achieve very high level of sensitivity, but this is accompanied with drop in specificity and not suitable for large epidemiological surveys which require extensive human and economic resources.

Boye et al.^[30] compared diagnostic performance for the detection of caries using photographs (taken with intra-oral camera) with an established visual examination method and histological sections as the reference standard and concluded that the photographic assessment method had higher sensitivity for caries detection than visual examination. The two methods had comparable specificities.

Paul et al.^[31] described a laser-supported dental endoscope, which is a combination of a customary intraoral camera with a laser as an illumination source. The use of a laser beam at 530 nm for illumination enables a significant presentation of early caries on tooth enamel. The laser-supported dental endoscope, employing a laser beam of 337 nm, is also suitable to detect early caries on the basis of the autofluorescence of the tooth enamel.

ELECTRICAL CONDUCTANCE MEASUREMENT (ECM)

The idea of an electrical method for caries detection was proposed by Magitot in 1878, and is based on the theory that sound dental hard tissue, especially the enamel, shows very high electrical resistance or impedance. In the impedance measurement system a circuit of a very weak alternating current is closed through the patient. From the device, a fiber leads to a probe, which is placed on the site that is to be measured.^[32]

Based on the differences in the electrical conductance of carious tissue and sound enamel, two instruments were developed and tested in 1980, i.e. Vanguard electronic caries detector and caries meter. In Vanguard electronic caries detector method, resistance measurements are made between a hand held connection and probe tip placed within the fissures of the teeth. Superficial saliva is removed to prevent surface conduction. Machine gives a reading on a scale of 0-9, which is directly proportional to the degree of demineralization. In caries meter method, the resistance measurement is made between the probe tip and clip attached to oral electrode, and colored light reflects the status of tooth.

The disadvantages are that the area of diagnosis is confined to the dimension of the probe, technique sensitivity as salivary or temperature changes can change measurements and the status of lesion is not known such as arrested or active. The advantages are small and handy systems, accurate diagnosis and no pain to the patient. Further, Sengun et al.^[33] found that the ECM is very useful at the diagnosis of occlusal caries which are difficult to detect clinically and in this way minimizes the risk of unnecessary tissue loss. With this device, it can be possible to avoid unnecessary radiographs.

Various studies have shown that ECM has higher sensitivity values (0.90) compared with conventional methods for detecting occlusal dentin caries lesions. However, lower specificity values (around 0.80) have been observed.^[34,35] In Ashley et al.^[36] study, surface-specific electrical measurements were recorded every 6 months during the second 18-month period of a 3-year clinical trial comparing two products whose relative anti-caries effects were unknown. Over an 18-month period, ECM measurements demonstrated a significant difference in the mean distributed file system increment between the test and the control groups. In contrast, the conventional detection methods used in the trial were unable to discriminate between the products over three years.

Improved diagnoses at the dentinal level were obtained, when EC and LF were used at higher cutoff values as an adjunct to visual inspection, as the latter rely exclusively on fissure discoloration. In cases of discolored fissures, these methods help to overcome false-positive identification of dentinal caries. However, attainable reliabilities of diagnoses do not seem to exceed about 50–60%.^[37]

Fennis-Ie et al.^[38] compared the performance of visual inspection on FOTI, and electrical conductance measurements (ECMs) and concluded that ECM is a better predictor of occlusal caries than fissure discoloration and FOTI. A cost-effective analysis is envisaged to obtain insight into the practical value of ECMs in the prediction of occlusal caries and, thus, into the effectiveness of sealant application.

RADIOGRAPHY

LASERS

OCT

The first OCT in the field of dentistry was performed by Colston et al. in 1998. It creates cross-sectional images of biological structures using, differences in reflection of light. Microstructural details are revealed by differentiating between scattered, transmitted, or reflected photons. Baumgartner et al.^[66] showed that it can provide additional information related to the mineralization status and/or the scattering properties of the dental materials.

Amaechi et al.^[67] investigated the correlation between fluorescence loss measured by QLF and the reflectivity loss measured by a OCT system in a demineralization process to produce artificial dental caries and concluded that the decrease in reflectivity of the enamel during demineralization, measured by OCT, could be related to the amount of mineral lost during the demineralization process.

Nguyen et al.^[68] reported that the diagnostic capability of OCT (78–88% sensitivity and 71–84% specificity) was best in superficial, inter-proximal areas, and margins of restorations and was least effective in deep caries at locations exceeding 2 mm depth and concluded that OCT is a rapidly developing, promising modality for in vivo real-time imaging with excellent capability for non-invasive early caries detection and monitoring.

SPECIES SPECIFIC MONOCLONAL ANTIBODIES

This was given by Shi et al. in 1998, identified specific monoclonal antibodies that recognize the surface of cariogenic bacteria. They used three highly species-specific monoclonal immunoglobulin G (IgG) antibodies targeted against Streptococcus mutans. The probes are tagged with fluorescent molecules that measure quantitatively with spectrometer.

Advantages include that it can be used at chairside by dentist, quick results, and the overall risk assessment can be made in operatory itself. Shi et al.^[69] developed three highly species-specific monoclonal IgG antibodies against S. mutans that quantitatively detect S. mutans in <1 min and is sensitive enough to detect a single bacterial cell and concluded that these methods could be widely used in basic and clinical studies related to S. mutans and in the clinical diagnosis and treatment of caries in humans. Gu et al.^[70] study showed that MAb-based salivary S. mutans tests exhibit significantly higher specificity and sensitivity than the commonly used selective culture method and thus provides useful information and tools for analyzing the role of S. mutans in human dental caries.

CARIESCAN

This device is based on alternating current impedance spectroscopy and involves the passing of an insensitive level of electrical current through the tooth to identify the presence and location of the decay. It is the first dental diagnostic tool to use an impedance spectroscopy to quantify dental caries early enough to enhance preventative treatment. CarieScan is not affected by optical factors such as staining or discoloration of the tooth. It provides a qualitative value based on the disease state rather than the optical properties of the tooth.^[71]

Bader et al.^[72] carried out a systematic review comparing CarieScan with a clinical visual examination, bitewing radiograph, and DIAGNOdent reported CarieScan to have superior sensitivity and specificity both 92.5% over other methods.

CONCLUSION

Advanced diagnostic technologies are increasingly playing a more key role in this process, both in data collection and assessment capabilities and the utilization of the information obtained. Diagnostic modalities available to clinicians to expand greatly on the foundation of a comprehensive visual assessment, which has been and will be the cornerstone of the diagnostic process.