Near-IR and CP-OCT imaging of suspected occlusal caries lesions

Clinical SWIR and CP-OCT imaging of interproximal lesions

BACKGROUND

Enamel is highly transparent at short wavelength infrared imaging (SWIR) wavelengths allowing the detection of dental decay without the need for ionizing radiation. The purpose of this study was to use SWIR imaging methods including cross polarization optical coherence tomography (CP-OCT), occlusal transillumination (SWIR-OT), proximal transillumination (SWIR-PT), and occlusal reflectance (SWIR-R) to image interproximal lesions in vivo and compare the sensitivity with radiography.

METHODS

Participants (n = 30) aged 18-80 each with a radiopositive interproximal lesion scheduled for restoration were enrolled in the study. Studies have shown that the opposing proximal surfaces across the contact will likely also have lesions. SWIR images were acquired of the adjoining teeth at each contact with an interproximal lesion scheduled for restoration. Lesion presence and depth were assessed on each side of the contact for radiography and each SWIR imaging method. Lesions on radiographs and in CP-OCT images were identified by a single examiner while lesions in SWIR images were identified by a contrast threshold via semi-automatic image segmentation.

RESULTS

All SWIR imaging methods had significantly higher sensitivity (P < 0.05) than radiographs for the detection of interproximal lesions on the teeth opposite those restored. CP-OCT and SWIR-R imaging methods had significantly higher sensitivity than the other methods. SWIR imaging methods showed significantly higher lesion contrast than radiography.

CONCLUSIONS

SWIR imaging methods can be used to detect interproximal lesions on posterior teeth with higher diagnostic performance than radiographs. CP-OCT appears well suited as a potential gold standard for the detection of interproximal lesions and assessment of their severity in vivo.

Short-Wavelength Infrared Imaging of Infected and Affected Dentin

Stains produced by bacteria or those found in blood and food byproducts accumulate in highly porous caries lesions. They can interfere with accurate diagnosis and the selective removal of carious tissue during cavity preparations. Short-wavelength infrared (SWIR) imaging studies have shown that stain molecules do not absorb light beyond 1200 nm. The objective of this study was to image affected and infected dentin atSWIR wavelengths. Sections of 3 mm thickness were cut from the extracted teeth with deep dentinal lesions. The sound (normal), affected (stained), and infected (demineralized) dentin on each section were examined with reflected light at wavelengths from 400 to 1700 nm, red and green fluorescence, and with optical coherence tomography (OCT). Microcomputed tomography (microCT) was used to measure the mineral density at each location investigated. Significant (p < 0.05) differences were observed in the reflected light intensity at 400-850 nm and for fluorescence between the sound, affected, and infected dentin. SWIR imaging did not show significant reductions in reflectivity for the affected and infected dentin. SWIR images may be valuable for monitoring the lateral spread of dentinal lesions on the occlusal surfaces of teeth.

Efficiency of Near-Infrared Technology in the Clinical Detection of Carious Lesions: A Systematic Review

The field of dentistry has seen various technological advances regarding caries detection, some lesions still prove to be difficult to detect. A reasonably new detection method, near-infrared (NIR), has shown good results in caries detection. This systematic review aims to compare NIR with conventional methods in terms of caries detection. Online databases (PubMed, Scopus, ScienceDirect, EBSCO, and ProQuest) were used for the literature search. The search was performed from January 2015 till December-2020. A total of 770 articles were selected, of that 17 articles qualified for the final analysis as per Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The articles were assessed according to a modified Critical Appraisal Skills Programme checklist, and then synthesis of the review started. The inclusion criteria were clinical trials done in vivo on teeth with active caries of vital or nonvital teeth. This review excluded nonpeer reviewed articles, case reports, case series, opinions, abstracts, non-English written articles, studies of subjects with arrested caries, or teeth with developmental defects of tooth structure and teeth having environmental defects of tooth structure, as well as in-vitro studies. The review compared near-infrared technology with radiography, visual inspection, and laser fluorescence in terms of caries detection, sensitivity, specificity, and accuracy. The sensitivity of NIR ranged from 99.1 to 29.1%. Studies showed that NIR exhibited higher sensitivity for occlusal enamel and dentin caries. The specificity of NIR ranged from 94.1 to 20.0%. In enamel and dentinal occlusal caries, NIR demonstrated lower specificity than that of radiograph. The specificity of NIR in early proximal caries was low. Accuracy was determined in 5 out of 17 studies where the values ranged from 97.1 to 29.1%. The accuracy of NIR was the highest for dentinal occlusal caries. NIR shows promising evidence as an adjunct in caries examination due to its high sensitivity and specificity; however, more studies are required to determine its full potential in different situations.

Saliva biomarkers in oral disease

Saliva is a versatile biofluid that contains a wide variety of biomarkers reflecting both physiologic and pathophysiologic states. Saliva collection is noninvasive and highly applicable for tests requiring serial sampling. Furthermore, advances in test accuracy, sensitivity and precision for saliva has improved diagnostic performance as well as the identification of novel markers especially in oral disease processes. These include dental caries, periodontitis, oral squamous cell carcinoma (OSCC) and Sjögren's syndrome (SS). Numerous growth factors, enzymes, interleukins and cytokines have been identified and are the subject of much research investigation. This review highlights current procedures for successful determination of saliva biomarkers including preanalytical factors associated with sampling, storage and pretreatment as well as subsequent analysis. Moreover, it provides an overview of the diagnostic applications of these salivary biomarkers in common oral diseases.

Monitoring lesion activity on primary teeth with CP-OCT and SWIR reflectance imaging

OBJECTIVE

The purpose of this study was to use cross polarization optical coherence tomography (CP-OCT) and short wavelength infrared imaging (SWIR) reflectance imaging to monitor changes in the structure and activity of early occlusal caries on primary teeth over a period of 6 months during intervention with fluoride.

METHODS

Participants (n = 29) aged 6-10 each with two suspected active occlusal lesions on primary teeth completed the study. Fluoride varnish was applied to tooth surfaces every 3-months and participants were instructed to brush twice daily with a fluoride toothpaste. Images were acquired using CP-OCT every 3 months for 6 months. SWIR reflectance images were acquired during forced air-drying of the lesions for 30 s at 0 and 6-months.

RESULTS

Most of the 42 lesions appeared initially active at baseline. Only 6 lesions appeared arrested at baseline based on the presence of a highly mineralized transparent surface layer (TSL) in CP-OCT images. At 6 months, 14 of the lesions appeared arrested including the 6 initially arrested lesions and the TSL thickness increased significantly (p < 0.0001). The mean lesion depth (Ld) and the integrated reflectivity over the lesion depth (ΔR) increased significantly (p < 0.05) after 6 months for the 42 lesions analyzed. SWIR reflectance images showed that there was a significantly higher (p < 0.05) delay before changes in intensity were measured for active lesions versus arrested lesions during lesion drying.

CONCLUSION

CP-OCT was able to monitor changes in lesion structure and activity including the formation of a highly mineralized TSL indicative of lesion arrest during nonsurgical intervention. Time-resolved SWIR reflectance imaging also shows that there are differences in the dehydration kinetics between active and arrested lesions. This study demonstrates two independent imaging methods that can be used to monitor changes in lesion activity over time.

Active Surveillance of Root Caries in Vivo with CP-OCT

The active surveillance of root caries lesions to monitor potential remineralization or decay progression is challenging for the clinician, due to unreliable diagnostic information. The conventional visual and tactile methods for assessing the lesion activity are not reliable, and the clinician is often unable to determine if the lesion is progressing or has been arrested. An important marker of an arrested lesion is a highly mineralized transparent surface zone (TSL) that forms when the mineral is deposited in the outer layer of the lesion. The purpose of this study was to determine if cross-polarization optical coherence tomography (CP-OCT) could be used to detect changes in the lesion severity and activity during active monitoring. In total, 18 subjects with 22 suspected active root caries lesions were evaluated using CP-OCT at the baseline, 3 months, and 6 months. All subjects were instructed to use a high fluoride dentifrice at the baseline. The results showed that CP-OCT was able to discriminate the active from the arrested lesions by identifying the presence of a TSL on arrested lesions. The results also indicated that the mean TSL thickness increased significantly (p < 0.05) for the nine lesion areas. In addition, CP-OCT was able to show the progression of demineralization, erosion, and changes in gingival contours in scanned areas. CP-OCT was valuable for monitoring the activity and severity of root caries lesions in vivo. CP-OCT can be used to assess the activity of root caries lesions at a single time point by detecting the presence of a TSL at the lesion surface indicative of the lesion arrest.

Mouthwash as a non-invasive method of indocyanine green delivery for near-infrared fluorescence dental imaging

SIGNIFICANCE

X-ray imaging serves as the mainstream imaging in dentistry, but it involves risk of ionizing radiation.

AIM

This study presents the feasibility of indocyanine green-assisted near-infrared fluorescence (ICG-NIRF) dental imaging with 785-nm NIR laser in the first (ICG-NIRF-I: 700 to 1000 nm) and second (ICG-NIRF-II: 1000 to 1700 nm) NIR wavelengths.

APPROACH

Sprague Dawley rats with different postnatal days were used as animal models. ICG, as a fluorescence agent, was delivered to dental structures by subcutaneous injection (SC) and oral administration (OA).

RESULTS

For SC method, erupted and unerupted molars could be observed from ICG-NIRF images at a short imaging time (<1  min). ICG-NIRF-II could achieve a better image contrast in unerupted molars at 24 h after ICG injection. The OA could serve as a non-invasive method for ICG delivery; it could also cause the glow-in-dark effect in unerupted molars. For erupted molars, OA can be considered as mouthwash and exhibits outstanding performance for delivery of ICG dye; erupted molar structures could be observed at a short imaging time (<1  min) and low ICG dose (0.05  mg  /  kg).

CONCLUSIONS

Overall, ICG-NIRF with mouthwash could perform in-vivo dental imaging in two NIR wavelengths at a short time and low ICG dose.

Current Status and Trends in Research on Caries Diagnosis: A Bibliometric Analysis

There are a wide variety of devices for the detection and diagnosis of caries from the initial stages. The purpose of this study was to perform a bibliometric study on research regarding caries diagnosis by identifying the contributing researchers, organizations, countries or regions, journals, and to provide an analysis of keyword co-occurrence and co-authorship networks. An advanced search was performed in Web of Science (WOS) Core Collection database, using the terms “caries diagno*” and “caries detect*” in the “topic” field, from 2013 to 2021. Bibliometric parameters were extracted using WOS’s analyze results tools and VOSviewer software. A total of 816 documents were identified. Most of them, (61.3%) are included in “Dentistry Oral Surgery & Medicine” category within WOS. The largest scientific production on the subject is observed between 2018 and 2021, with a total of 344 records. The most productive author is Mendes FM, followed by Braga MM. The journal with the most articles published on caries diagnosis is Caries Research, with 55 articles (6.74%). The terms with the highest co-occurrence refer to the validity of diagnostic methods, tools or principles used in diagnosis or general aspects related to caries detection and diagnosis.

Evaluating interproximal and occlusal lesion severity with a dual SWIR transillumination/reflectance probe

We have developed a clinical probe capable of acquiring simultaneous, multispectral short wavelength infrared (SWIR) reflectance and occlusal transillumination images of lesions on tooth proximal and occlusal surfaces to reduce the potential of false positives and enhance diagnosis. The dual probe was 3D printed and the imaging system uses an InGaAs camera and broadband light sources at 1310 nm for occlusal transillumination and 1600 nm for cross-polarization reflectance measurements. In this study a mathematical model to estimate the penetration depth of "hidden" occlusal lesions from the SWIR images was developed. We compared the model's estimated lesion depth on 18 extracted teeth with lesions against microCT measurements. Although the model estimated depth deviates from that measured in microCT at higher depths, there is a good linear correlation (R² = 0.93) between the estimated depth from SWIR images and the measured depth using microCT. SWIR occlusal transillumination images at 1300 nm also provide information about interproximal lesion penetration depth which can be directly viewed from the occlusal surface. SWIR occlusal transillumination and reflectance depth measurements on 49 natural interproximal lesions were compared with microCT measurements. There was significant correlation between the depths measured with SWIR occlusal transillumination (R² = 0.81) and reflectance (R² = 0.19) compared with the depths measured with microCT.

Dual short wavelength infrared transillumination/reflectance mode imaging for caries detection

SIGNIFICANCE

We have developed a clinical probe capable of acquiring near-simultaneous short-wavelength infrared (SWIR) reflectance and occlusal transillumination images of lesions on tooth proximal and occlusal surfaces. We hypothesize that dual images will aid in differentiating between shallow and deep occlusal lesions and reduce the potential of false positives (FPs).

AIM

The aim of this study was to test the performance of the dual reflectance and occlusal transillumination probe on extracted teeth prior to commencing clinical studies.

APPROACH

The dual probe was 3D printed and the imaging system uses an InGaAs camera and broadband superluminescent diode light sources that emit broadband light at 1300 nm for occlusal transillumination and 1600-nm light for cross-polarization reflectance. The diagnostic performance of the dual probe was assessed using 120 extracted teeth with approximal and occlusal lesions. Reflectance and transillumination images were fused into single images to enhance the contrast between sound and lesion areas. The lesion contrast in both modes did not increase significantly with either the lesion depth or the distance from the occlusal surface for approximal lesions. In addition, the diagnostic performance of radiography, the individual reflectance and transillumination images, dual images, and fused images were compared using micro-computed tomography as the gold standard.

RESULTS

Reflectance imaging at 1600 nm yielded the highest diagnostic accuracy for lesions on both occlusal and proximal surfaces while radiography yielded the lowest number of FPs.

CONCLUSION

This study demonstrates that simultaneous acquisition of both reflectance and transillumination SWIR images is possible with a single clinical device.

Quantitative Classification of 3D Collagen Fiber Organization From Volumetric Images

Collagen fibers in biological tissues have a complex 3D organization containing rich information linked to tissue mechanical properties and are affected by mutations that lead to diseases. Quantitative assessment of this 3D collagen fiber organization could help to develop reliable biomechanical models and understand tissue structure-function relationships, which impact diagnosis and treatment of diseases or injuries. While there are advanced techniques for imaging collagen fibers, published methods for quantifying 3D collagen fiber organization have been sparse and give limited structural information which cannot distinguish a wide range of 3D organizations. In this article, we demonstrate an algorithm for quantitative classification of 3D collagen fiber organization. The algorithm first simulates five groups, or classifications, of fiber organization: unidirectional, crimped, disordered, two-fiber family, and helical. These five groups are widespread in natural tissues and are known to affect the tissue's mechanical properties. We use quantitative metrics based on features such as preferred 3D fiber orientation and spherical variance to differentiate each classification in a repeatable manner. We validate our algorithm by applying it to second-harmonic generation images of collagen fibers in tendon and cervix tissue that has been sectioned in specified orientations, and we find strong agreement between classification from simulated data and the physical fiber organization. Our approach provides insight for interpreting 3D fiber organization directly from volumetric images. This algorithm could be applied to other fiber-like structures that are not necessarily made of collagen.

3D imaging of proximal caries in posterior teeth using optical coherence tomography

Optical coherence tomography (OCT) can create cross-sectional images of tooth without X-ray exposure. This study aimed to investigate the diagnostic accuracy of 3D imaging of OCT for proximal caries in posterior teeth. Thirty-six human molar teeth with 51 proximal surfaces visibly 6 intact, 16 slightly demineralized, and 29 distinct carious changes were mounted to take digital radiographs and 3D OCT images. The sensitivity, specificity and area under the receiver operating characteristic curve (AUC) for the diagnosis of enamel caries and dentin caries were calculated to quantify the diagnostic ability of 3D OCT in comparison with digital radiography. Diagnostic accuracy was evaluated by the agreement with histology using weighted Kappa. OCT showed significantly higher sensitivity, AUC and Kappa values than radiography. OCT can be a safer option for the diagnosis of proximal caries in posterior teeth that can be applied to the patients without X-ray exposure.

Thermal Imaging of Root Caries In Vivo

Improved methods are needed to assess the structure and activity of lesions on root surfaces in order to improve clinical decision making. Conventional visual and tactile methods for assessing lesion activity are not reliable, and the clinician is often unable to evaluate if the lesion is progressing or has remineralized. An important marker of an arrested lesion is a highly mineralized surface zone that forms when mineral is deposited in the outer layer of the lesion. In vitro studies have shown that a mineralized surface zone influences the kinetics of water evaporation and the surface temperature while drying. Temperature changes can be monitored by measuring the thermal emission with thermal imaging. Studies have also shown that the depth and severity of demineralization and the thickness of the highly mineralized transparent surface zone on arrested lesions can be measured nondestructively with optical coherence tomography (OCT). Thermal imaging at 8-µm to 13-µm wavelengths was completed on 30 test subjects with a suspected active root caries lesion by monitoring thermal emission from the tooth surfaces during 30 s of air drying. Lesions were also evaluated using cross-polarization OCT (CP-OCT) during lesion dehydration to identify transparent surface zones indicative of arrested lesions and determine if shrinkage occurred during drying. The overall thermal emission recorded during drying was significantly different (P < 0.001) when comparing sound tooth surfaces, lesion areas identified as arrested, and lesion areas identified as active, demonstrating that thermal imaging is a promising approach for the clinical assessment of lesion activity on root surfaces. Ten of the lesions in this study had distinct areas with transparent surface zones that were visible in CP-OCT images. Shrinkage was detected with CP-OCT during drying for 12 lesions. This study confirms that these novel approaches for assessing lesion activity on root surfaces can be implemented in vivo.

Occlusal Caries Detection and Diagnosis Using Visual ICDAS Criteria, Laser Fluorescence Measurements, and Near-Infrared Light Transillumination Images

OBJECTIVE

Current diagnostic tools for non-cavitated occlusal caries are not very reliable. For this reason, newer systems need to be developed. The aim of this study was to compare the performance of visual inspection (ICDAS-II), laser fluorescence (DIAGNOdent pen), and the near-infrared transillumination technique (DIAGNOcam) in the detection of non-cavitated occlusal caries lesions under clinical and laboratory conditions in 90 third molar teeth planned for extraction.

MATERIALS AND METHODS

Ninety third molar teeth were firstly examined in clinical conditions, scored according to ICDAS-II criteria, and examined with DIAGNOdent pen and DIAGNOcam devices. After finishing the clinical examination, the teeth were re-evaluated shortly after the extractions with the same methods. Then, the teeth were sectioned for histological validation according to Downer's criteria. Sensitivity, specificity, accuracy, and area under the receiver operating characteristic (ROC) curves were calculated based on the histological results.

RESULTS

For the D0-D1-4 threshold, the area under the ROC curve values ranged between 0.754 and 0.881 for all systems. Sensitivity values ranged between 80.5 and 96.1%, and specificity values ranged between 61.5 and 84.6% for the three caries detection methods. DIAGNOcam had the best correlation value (0.616) according to histological observations and demonstrated a sensitivity rate of 96.1%, a specificity rate of 61.5%, and an accuracy rate of 91.1%.

CONCLUSIONS

DIAGNOcam was found to be the most effective method for the diagnosis of occlusal caries without cavitation in permanent molar teeth.

3D Dental Subsurface Imaging Using Enhanced Truncated Correlation-Photothermal Coherence Tomography

Development of accurate and sensitive dental imaging technologies is a top priority in the pursuit of high-quality dental care. However, while early dental caries detection and routine monitoring of treatment progress are crucial for effective long-term results, current radiographic technologies fall short of this objective due to low sensitivity for small lesions and use of ionizing radiation which is unsuitable for frequent monitoring. Here we demonstrate the first application of enhanced Truncated Correlation-Photothermal Coherence Tomography (eTC-PCT) to dental imaging. eTC-PCT is non-invasive and non-ionizing, operates well below the maximum permissible exposure (MPE) limit, and features 3D subsurface imaging capability with operator controlled axial resolution. We explore the potential of this method for dental applications and demonstrate its capability for depth-resolved tomographic 3D reconstructions of the details and subsurface extent of a variety of dental defects. To this end, in this proof-of-concept study, dental eTC-PCT imaging results, and its sensitivity to dental caries, are discussed in comparison with visual examination, x-rays and micro-CT imaging.

Combined Near-Infrarred Light Transillumination and Direct Digital Radiography Increases Diagnostic In Approximal Caries

The objective of this study was to evaluate the clinical ability of Near-Infrared Light-Transillumination (NILT) for approximal dentinal caries detection and to compare with direct digital-radiography (DDR), as well as to determine whether the combination of both techniques improves the diagnostic capacity of the lesions. From 88 patients (over 18 years), 138 posterior teeth (76 molars and 62 premolars), that had approximal caries reached into dentine determined by DDR, were included. Lesion extension and DDR images were scored as follows: D0 = sound surface, D1/D2 = caries restricted to the outer/inner-half of the enamel, and D3/4 = caries restricted to the outer/inner-half of the dentin. Opening of the approximal surface using 0.5 mm-in-diameter diamond-bar was used as gold-standard. The lesion extension was then determined by the following criteria: no dentinal caries (D0/1/2) or dentinal caries (D3/4). Seventy-one lesions were D3 and 67 lesions were D4. Sensitivities of overall/D3/D4 were 98.0/95.7/100.0 (NILT) and 100/100/100 (DDR), respectively. Correlations with gold-standard were 0.92 (NILT) and 0.42 (DDR), respectively. The correlation increased to 0.97 (p = 0.045) on combining NILT and DDR. There was no difference in sensitivity between the methods (p > 0.05); but was differences in the correlation (p < 0.01). It can be concluded that NILT showed sensitivity similar to that of DDR and higher correlation than DDR for approximal dentinal caries detection. Accordingly, it may be used to monitor the progression of caries without exposing the patient to ionizing radiation, this being of particular interest in growing patients and in pregnant women. In this respect, NILT can be an effective diagnostic tool adjunctive to bitewing radiographs in detecting approximal dentinal caries. The combination of NILT and DDR represents an increase in the diagnosis of approximal lesions The proposed diagnostic protocol comprises visual examination, followed by NILT and DDR only if the former technique detects approximal caries.

Adaptation Assessment of Three Bonded Resin Restorations at the Cavity Floor Using Cross-Polarization Optical Coherence Tomography

Objective: The aim of the study was to compare the composite adaptation of three systems by using cross-polarization optical coherence tomography (CP-OCT). Background data: Most polymer-based restorations suffer from polymerization shrinkage that affects the interfacial seal. This shrinkage cannot be detected by conventional X-ray methods. Optical coherence tomography was proved to be a reliable non-invasive imaging tool to examine biological structures and biomaterials at micron scale. Methods: Twenty-four cylindrical class-V cavities were prepared on the buccal surfaces of the extracted human molars. After cavity preparation, samples were randomly divided into three groups (n = 8) according to the restoration system: one-step self-etch Clearfil Tri-S Bond Plus with Clearfil Majesty ES-2 composite (TS; Kuraray Noritake Dental), Single Bond Universal in self-etch mode with Filtek Z350 XT composite (SB; 3M ESPE), and one-step self-etch Plafique Bond with Plafique LX 5 composite (PB; Tokuyama Dental). The restoration placement was carried out according to the manufacturers' recommendations. Later, the specimens were immersed in a contrasting agent; then, image acquisitions were taken by CP-OCT to calculate the adaptation percentage by using an image analysis software. Results: Mann-Whitney U test showed no statistical significant difference in the adaptation percentage between TS (91.72 ± 11.6) and SB (93.43 ± 6.9) groups (p > 0.05). However, the adaptation percentage in PB (41.83 ± 28.5) was significantly lower than in the other tested groups (p < 0.05). Conclusions: Within the limitation of the study, TS and SB groups showed better adaptation than PB. Moreover, CP-OCT is a useful imaging tool that can display composite adaptation at micron scale.

Indocyanine green-assisted dental imaging in the first and second near-infrared windows as compared with X-ray imaging

Indocyanine green (ICG) has been widely used in medical imaging, such as in retinal angiography. Here, we describe a pilot ex vivo study of ICG-assisted near-infrared fluorescence (NIRF) dental imaging in the first (700-950 nm for ICG-NIRF-I) and second (1000-1700 nm for ICG-NIRF-II) NIR windows using human extracted teeth; our study is compared with the traditional prevalent X-ray imaging and NIR II illumination (NIRi-II, 1310 nm) without ICG enhancement. The results show that ICG fluorescence has much better imaging contrast in both windows compared with NIRi-II (by quantitatively comparing NIR intensity of the critical neighboring structures, such as enamel and dentin). Cracked teeth, notoriously hard to diagnose by dental X-ray and computed tomography, were clearly profiled in NIRF dental imaging. An insidious occlusal caries, missing in X-ray imaging, became a bright dot that was readily observed in ICG-NIRF-I images. For dental decay, NIRF imaging with ICG enhancement could clearly delineate the decay boundary. NIRF in both windows distinguished interproximal and occlusal superficial caries. Overall, ICG-assisted NIRF dental imaging has unique advantages in identifying cracked teeth and insidious caries. The two NIR imaging windows used in our study might one day serve as noninvasive and nonionizing-radiation methods for the diagnosis of critical dental diseases in situ.

Optical Coherence Tomography

Optical coherence tomography (OCT) is a noninvasive diagnostic technique providing cross-sectional images of biologic structures based on the differences in tissue optical properties. OCT has been widely used in numerous clinical applications and is becoming popular as a promising technology in dentistry. Today, dental hard (tooth) and soft (hard palate mucosa and gingiva mucosa) tissues are visualized with OCT. With new developments in technology, the applications of OCT are being investigated in various fields in dentistry, such as to detect microleakage around restoration, tooth cracks/fractures, examination of periodontal tissues/pockets, early detection of oral cancerous tissues, and in endodontics for location of pulp canal.

Fluorescence and Near-Infrared Light Transillumination

This article describes the current applications of various technologies based on either autofluorescence or near-infrared light illumination, tailored to aid practitioners in detecting and quantitatively monitoring oral diseases such as dental caries and oral cancer at the earliest stage of their formation, or in the conservative surgical excision of necrotic bones in diseases such as chronic osteomyelitis, osteoradionecrosis, and medication-related osteonecrosis of the jaw. The data discussed are primarily based on published scientific studies and reviews from case reports, clinical trials, and in vitro and in vivo studies. References have been traced manually, by MEDLINE, or through manufacturer's websites.

Imaging of demineralized enamel in intact tooth by epidetected stimulated Raman scattering microscopy

Stimulated Raman scattering microscopy (SRS) was deployed to quantify enamel demineralization in intact teeth. The surfaces of 15 bovine-enamel blocks were divided into four equal-areas, and chemically demineralized for 0, 8, 16, or 24 h, respectively. SRS images (spectral coverage from ∼850 to 1150  cm  -  1) were obtained at 10-μm increments up to 90  μm from the surface to the dentin-enamel junction. SRS intensities of phosphate (peak: 959  cm  -  1), carbonate (1070  cm  -  1), and water (3250  cm  -  1) were measured. The phosphate peak height was divided by the carbonate peak height to calculate the SRS-P/C-ratio, which was normalized relative to 90  μm (SRS-P/C-ratio-normalized). The water intensity against depth decay curve was fitted with exponential decay. A decay constant (SRS-water-content) was obtained. Knoop-hardness values were obtained before (SMHS) and after demineralization (SMHD). Surface microhardness-change (SMH-change) [  (  SMHD  -  SMHS  )    /  SMHS] was calculated. Depth and integrated mineral loss (ΔZ) were determined by transverse microradiography. Comparisons were made using repeated-measures of analysis of variance. For SRS-P/C-ratio-normalized, at 0-μm (surface), sound (0-h demineralization) was significantly higher than 8-h demineralization and 24-h demineralization; 16-h demineralization was significantly higher than 24-h demineralization. For SRS-water-content, 24-h demineralization was significantly higher than all other demineralization-groups; 8-h demineralization and 16-h demineralization were significantly higher than 0-h demineralization. SRS-water-content presented moderate-to-strong correlation with SMH-change and weak-to-moderate correlation with depth. These results collectively demonstrate the potential of using SRS microscopy for in-situ chemical analysis of dental caries.

Comparative study on the detection of early dental caries using thermo-photonic lock-in imaging and optical coherence tomography

Early detection of dental caries is known to be the key to the effectiveness of therapeutic and preventive approaches in dentistry. However, existing clinical detection techniques, such as radiographs, are not sufficiently sensitive to detect and monitor the progression of caries at early stages. As such, in recent years, several optics-based imaging modalities have been proposed for the early detection of caries. The majority of these techniques rely on the enhancement of light scattering in early carious lesions, while a few of them are based on the enhancement of light absorption at early caries sites. In this paper, we report on a systemic comparative study on the detection performances of optical coherence tomography (OCT) and thermophotonic lock-in imaging (TPLI) as representative early caries detection modalities based on light scattering and absorption, respectively. Through controlled demineralization studies on extracted human teeth and µCT validation experiments, several detection performance parameters of the two modalities such as detection threshold, sensitivity and specificity have been qualitatively analyzed and discussed. Our experiment results suggests that both modalities have sufficient sensitivity for the detection of well-developed early caries on occlusal and smooth surfaces; however, TPLI provides better sensitivity and detection threshold for detecting very early stages of caries formation, which is deemed to be critical for the effectiveness of therapeutic and preventive approaches in dentistry. Moreover, due to the more specific nature of the light absorption contrast mechanism over light scattering, TPLI exhibits better detection specificity, which results in less false positive readings and thus allows for the proper differentiation of early caries regions from the surrounding intact areas. The major shortcoming of TPLI is its inherent depth-integrated nature, prohibiting the production of depth-resolved/B-mode like images. The outcomes of this research justify the need for a light-absorption based imaging modality with the ability to produce tomographic and depth-resolved images, combining the key advantages of OCT and TPLI.

Effect of self-etch adhesives on the internal adaptation of composite restoration: a CP-OCT Study

Despite improvements in dental adhesive materials, internal adaptation remains a challenge in bonded restorations. The aim of this study was to compare microgaps and internal floor adaptation between two different self-etch adhesives in class-V cavities using cross-polarization optical coherence tomography (CP-OCT). In this in vitro study, standardized round class-V cavities were prepared in 20 non-carious human upper central incisor teeth. They were randomly divided into two groups, TN and SE, with each group receiving a different dental adhesive. In TN group, the adhesive used was all-in-one Tetric N-Bond Self-Etch (TN; Ivoclar/Vivadent, Liechtenstein), while SE group was bonded with two-step self-etch Clearfil SE Bond 2 adhesive (SE; Kuraray Noritake Dental Inc, Japan). The prepared cavities were restored with flowable composite and then stored in distilled water for 24 h. Next, they were immersed in silver nitrate, followed by immersion in a photo-developing solution. Optical comparison was carried out by CP-OCT to assess microgaps and composite adaptation at the cavity floor. A Mann-Whitney test was applied to the data, which showed a statistically significant difference in composite adaptation among the two groups (p < 0.001) with the SE group showing superior adaptation. CP-OCT is a reliable tool for non-invasive imaging that gives an insight into composite performance. Better adaptation was found with the two-step self-adhesive for the composite used in this study.

Multispectral near-infrared reflectance and transillumination imaging of occlusal carious lesions: Variation in lesion contrast with lesion depth

In vivo and in vitro studies have demonstrated that near-infrared (NIR) light at λ=1300-1700-nm can be used to acquire high contrast images of enamel demineralization without interference of stains. The objective of this study was to determine if a relationship exists between the NIR image contrast of occlusal lesions and the depth of the lesion. Extracted teeth with varying amounts of natural occlusal decay were measured using a multispectral-multimodal NIR imaging system which captures λ=1300-nm occlusal transillumination, and λ=1500-1700-nm cross-polarized reflectance images. Image analysis software was used to calculate the lesion contrast detected in both images from matched positions of each imaging modality. Samples were serially sectioned across the lesion with a precision saw, and polarized light microscopy was used to measure the respective lesion depth relative to the dentinoenamel junction. Lesion contrast measured from NIR cross-polarized reflectance images positively correlated (p<0.05) with increasing lesion depth and a statistically significant difference between inner enamel and dentin lesions was observed. The lateral width of pit and fissures lesions measured in both NIR cross-polarized reflectance and NIR transillumination positively correlated with lesion depth.

The Use of Optical Coherence Tomography in Dental Diagnostics: A State-of-the-Art Review

Optical coherence tomography provides sections of tissues in a noncontact and noninvasive manner. The device measures the time delay and intensity of the light scattered or reflected from biological tissues, which results in tomographic imaging of their internal structure. This is achieved by scanning tissues at a resolution ranging from 1 to 15 μm. OCT enables real-time in situ imaging of tissues without the need for biopsy, histological procedures, or the use of X-rays, so it can be used in many fields of medicine. Its properties are not only particularly used in ophthalmology, in the diagnosis of all layers of the retina, but also increasingly in cardiology, gastroenterology, pulmonology, oncology, and dermatology. The basic properties of OCT, that is, noninvasiveness and low wattage of the used light, have also been appreciated in analytical technology by conservators, who use it to identify the quality and age of paintings, ceramics, or glass. Recently, the OCT technique of visualization is being tested in different fields of dentistry, which is depicted in the article.

Assessment of cavitation in artificial approximal dental lesions with near-IR imaging

Bitewing radiography is still considered state-of-the-art diagnostic technology for assessing cavitation within approximal carious dental lesions, even though radiographs cannot resolve cavitated surfaces but instead are used to measure lesion depth in order to predict cavitation. Clinicians need new technologies capable of determining whether approximal carious lesions have become cavitated because not all lesions progress to cavitation. Assessing lesion cavitation from near-infrared (NIR) imaging methods holds great potential due to the high transparency of enamel in the NIR region from λ=1300-1700-nm, which allows direct visualization and quantified measurements of enamel demineralization. The objective of this study was to measure the change in lesion appearance between non-cavitated and cavitated lesions in artificially generated lesions using NIR imaging modalities (two-dimensional) at λ =1300-nm and λ=1450-nm and cross-polarization optical coherence tomography (CP-OCT) (thee-dimensional) λ =1300-nm. Extracted human posterior teeth with sound proximal surfaces were chosen for this study and imaged before and after artificial lesions were made. A high speed dental hand piece was used to create artificial cavitated proximal lesions in sound samples and imaged. The cavitated artificial lesions were then filled with hydroxyapatite powder to simulate non-cavitated proximal lesions.