Polarization-sensitive optical coherence tomography of dental structures

Exploratory Analysis of Objective Outcome Measures for the Clinical Assessment of Erosive Tooth Wear

This study proposed using enamel surface texture and thickness for the objective detection and monitoring of erosive tooth wear (ETW), comparing them to the standard subjective Basic Erosive Wear Evaluation (BEWE). Thirty-two subjects (n = 597 teeth) were enrolled in this longitudinal observational clinical study. Enamel thickness (by cross-polarization optical coherence tomography, CP-OCT) and 3D dental microwear parameters, i.e., area-scale fractal complexity (Asfc), anisotropy (Str), and roughness (Sa) (by white-light scanning confocal profilometry), were obtained from buccal surfaces. Buccal, occlusal, and lingual surfaces were scored for BEWE and the maximum score per tooth (BEWEMax) was determined at baseline and 12 months (M12). Data outcome relationships were evaluated (alpha = 0.05). Enamel thickness decreased (p < 0.001), BEWE scores, Sa, and Str increased (p < 0.001), while Asfc did not change at M12. Baseline BEWEBuccal correlated strongly with BEWEMax (r = 0.86, p < 0.001) and moderately with BEWELingual (r = 0.42, p < 0.001), but not with enamel thickness (r = 0.03, p = 0.43). Change (Δ) in surface texture outcomes correlated poorly but significantly with ΔBEWEBuccal (r = -0.15-0.16, p < 0.001) and did not correlate with Δenamel thickness (r = 0.02-0.09, p > 0.06). Teeth with BEWE progression revealed a greater increase in ΔSa and ΔStr. These findings suggest that enamel surface roughness can potentially determine ETW severity, and CP-OCT may be relevant for clinically monitoring enamel thickness.

Visible wavelength time-stretch optical coherence tomography

Visible light optical coherence tomography (OCT) is an emerging non-invasive imaging modality that offers new opportunities for anatomical and functional imaging of biological tissues. Time-stretch dispersive Fourier transform, also known as photonic time-stretch, is an all-optical processing method that enables real-time Fourier transformation of ultrafast optical signals and allows for OCT at high A-scan rates. In this work, a working prototype of a photonic time-stretch OCT (TS-OCT) method in the visible wavelength region is proposed and experimentally demonstrated. The proposed visible-light TS-OCT system achieves unprecedented throughput of 100 giga voxels/second and OCT volume rate of 4,000 volumes/second and can be used to expand the range of applications of TS-OCT systems.

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.

Assessment of demineralized tooth lesions using optical coherence tomography and other state-of-the-art technologies: a review

Tooth demineralization is one of the most common intraoral diseases, encompassing (1) caries caused by acid-producing bacteria and (2) erosion induced by acid of non-bacterial origin from intrinsic sources (e.g. stomach acid reflux) and extrinsic sources (e.g. carbonated drinks). Current clinical assessment based on visual-tactile examination and standardized scoring systems is insufficient for early detection. A combination of clinical examination and technology is therefore increasingly adapted. This paper reviews various procedures and technologies that have been invented to diagnose and assess the severity of tooth demineralization, with focus on optical coherence tomography (OCT). As a micron-resolution non-invasive 3D imaging modality, variants of OCT are now available, offering many advantages under different working principles for detailed analytical assessment of tooth demineralization. The roles, capabilities and impact of OCT against other state-of-the-art technologies in both clinical and research settings are described. (139 words).

Evaluation of Incipient Enamel Caries at Smooth Tooth Surfaces Using SS-OCT

(1) Background: Dental caries, if diagnosed at the initial stage, can be arrested and remineralized by a non-operative therapeutic approach preserving tooth structure. Accurate and reproducible diagnostic procedure is required for the successful management of incipient caries. The aim of this study was to evaluate the diagnostic accuracy of 3D swept-source optical coherence tomography (3D SS-OCT) for enamel caries at smooth tooth surface if the lesion was with remineralization. (2) Methods: Forty-seven tooth surfaces of 24 extracted human teeth visibly with/without enamel caries (ICDAS code 0−3) were selected and used in this study. The tooth surfaces of investigation site were cleaned and visually examined by four dentists. After the visual inspection, SS-OCT scanning was performed onto the enamel surfaces to construct a 3D image. The 2D tomographic images of the investigation site were chosen from the 3D dataset and dynamically displayed in video and evaluated by the examiners. A five-rank scale was used to score the level of enamel caries according to the following; 1: Intact enamel. 2: Noncavitated lesion with remineralization. 3: Superficial noncavitated lesion without remineralization. 4: Deep nonvacitated lesion without remineralization. 5: Enamel lesion with cavitation. Sensitivity and specificity for 3D OCT image and visual inspection were calculated. Diagnostic accuracy of each diagnostic method was calculated using weighted kappa. Statistical significance was defined at p = 0.05. (3) Results: 3D SS-OCT could clearly depict enamel caries at smooth tooth surface as a bright zone, based on the increased backscattering signal. It was noted that 3D SS-OCT showed higher sensitivity for the diagnosis of remineralized lesions and deep enamel lesions without cavitation, as well as cavitated enamel lesions (p < 0.05). No significant difference of specificity was observed between the two diagnostic methods (p > 0.05). Furthermore, 3D SS-OCT showed higher diagnostic accuracy than visual inspection (p < 0.05). (4) Conclusions: Within the limitations of this in vitro study, 3D SS-OCT showed higher diagnostic capacity for smooth surface enamel caries than visual inspection and could also discriminate lesion remineralization of enamel caries.

Dental Age Estimation Using Multiphoton Microscopy: A Potential Tool for Forensic Science

Normal aging affects the different structures of teeth, in particular, the dentine. These changes are useful in forensic disciplines as a tool for age estimation. Although multiphoton (MP) microscopy has been used to explore dental pieces, a relationship between age and MP response of the human dentine has not been proposed yet. The relationship between MP signals and natural dentine aging is investigated herein. An index of age (INAG) combining two-photon excitation fluorescence (TPEF) and second harmonic generation (SHG) images has been used to quantify these changes. The results show that the INAG significantly decreases with age. Moreover, peritubular dentine size and collagen internal properties are also modified with age. This information confirms the usefulness of this technique in forensic age estimation after disasters (natural or manmade) with a lack of comprehensive fingerprint database. Courts and other government authorities might also benefit from this tool when the official age of individuals under special circumstances is required for legal or medical reasons.

Tooth Wear and Tribological Investigations in Dentistry

Dental or tooth wear is a physiological process in the life cycle of teeth. Loss of the occlusal surface may cause excessive tooth wear. Several factors may contribute to tooth wear with different intensities and duration in the oral cavity. The oral cavity is generally compared to a tribological system to determine the various types of wear between teeth and restorative materials and assess the amount of dental wear. However, it is challenging to investigate in vitro and in vivo wear owing to the complexity of tooth wear; thus, a clear correlation between in vitro and in vivo data could not be established. This review is aimed at providing an insight into the etiology of tooth wear and tribological investigations in dentistry.

Caries inhibition of simulated active caries lesions with CO2 laser irradiation and fluoride

It has been well established that CO₂ laser irradiation can be used to transform the mineral phase of dental enamel to make it more resistant to acid dissolution. The purpose of this study was to investigate if carbon dioxide laser irradiation and topical fluoride can be used to treat incipient caries lesions to inhibit further progression, i.e. treat active lesion surfaces as opposed to sound surfaces prior to subjecting them to an acid challenge. Simulated active caries lesions were produced on twenty eight bovine enamel samples using a pH cycling model and those surfaces were irradiated by a 9.4 μm CO₂ laser and treated with topical fluoride. Changes in the surface morphology, acid resistance, and permeability were measured using digital microscopy, optical coherence tomography (OCT), and SWIR reflectance surface dehydration rate measurements at 1950 nm after exposure to a further acid challenge. There was a significant reduction (P < 0.05) of further lesion progression for lesion windows treated with CO₂ laser irradiation followed by the application of an acidulated phosphate fluoride gel compared to the untreated lesion windows on each sample. Treatment by laser irradiation alone was not effective. The degree of lesion inhibition was not as high as has been previously observed for laser irradiated sound enamel surfaces exposed to an acid challenge.

Cross-polarization optical coherence tomographic assessment of in situ simulated erosive tooth wear

This clinical study tested cross-polarization optical coherence tomography (CP-OCT) monitoring of erosive tooth wear (ETW). Twenty participants completed a 14-day/arm, 3-arm crossover study simulating different ETW severities. Participants received two enamel specimens (per arm) and were randomized to: severe (s-ETW, lemon juice/pH:2.5/4.25%wt/vol citric acid), moderate (m-ETW, grapefruit juice/pH:3.5/1.03%wt/vol citric acid), and non-ETW (water). Enamel thickness was measured with CP-OCT (day[D] 0, 7, 14) and micro-computed tomography (μ-CT; D14). Enamel surface loss was determined with CP-OCT and optical profilometry (OP; D7, D14). CP-OCT showed higher enamel surface loss for D14 than D7 for m-ETW (P = .009) and s-ETW (P = .040) and differentiated severity at D14 (s-ETW > non-ETW, P = .027). OP was able to differentiate surface loss between days (D7 < D14, P < .001) for m-ETW and s-ETW, and ETW severity effect after 7 and 14 days (non-ETW < m-ETW < s-ETW, P < .001). At D14, CP-OCT and μ-CT were positively correlated (r = .87, ICC = .62). CP-OCT showed potential as a tool for clinical ETW monitoring.

Non-Invasive Optical Coherence Tomography Data-Based Quantitative Algorithm for the Assessment of Residual Adhesive on Bracket-Removed Dental Surface

The aim of this study was to quantitatively assess the residual adhesive on orthodontic ceramic bracket-removed dental surface. In orthodontic process, ceramic bracket was repeated debonding physically, then the adhesive remained on the dental surface. The residual adhesive caused a lack of adhesive strength between dental and ceramic bracket. Since commonly used adhesive in orthodontics is translucent, residual adhesive is hard to be detected with conventional microscopes. Therefore, 1310 nm center wavelength swept-source OCT system based on laboratory customized image processing algorithm was used for the precise detection of residual adhesive on tooth surface. The algorithm separates residual adhesive from dental surface by comparing the height of adjacent B-scan images, while providing color-scaled images emphasizing the thickness information of residual adhesive. Finally, the acquired results were compared with microscopic and adhesive remnant index scoring gold standards, while the comparison confirmed the potential merits and the improvements of the proposed method over gold standards.

Comparative evaluation of the spectral-domain optical coherence tomography and microhardness for remineralization of enamel caries lesions

This study aimed to evaluate the Cirrus high-definition (HD) spectral-domain optical coherence tomography (SD-OCT) for the remineralization of artificial enamel caries and to compare it with the comparison surface microhardness (SMH) analysis. Artificial caries lesions were produced on forty human enamel samples. Then, three different remineralization agents containing casein phosphopeptide amorphous calcium phosphate; casein phosphopeptide amorphous calcium fluoride phosphate; calcium glycerophosphate, magnesium chloride, and xylitol; and remineralization solution (control) were applied with pH cycling for six days. The optical depth of backscattered light and microhardness of enamel were measured using SD-OCT and SMH. All remineralization agents were significantly efficient in reducing optical lesion depth on enamels (p₁=0.001, p₂=0.002, p₃=0.006, p₄=0.025), and in increasing the SMH of enamels (p_1-3=0.005, p₄=0.017). However, the optical lesion depths of the enamel showed no correlation with the SMH in the groups. In conclusion, demineralization and remineralization of artificial lesions can be assessed with both SD-OCT and SMH.

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.

Diagnostic accuracy of 870-nm spectral-domain OCT with enhanced depth imaging for the detection of caries beneath ceramics

OBJECTIVES

To evaluate the diagnostic accuracy of optical coherence tomography (OCT) for the non-invasive detection of caries adjacent to ceramic materials.

METHODS

Disks made from five ceramic materials (hybrid ceramic, feldspathic ceramic, zirconia-reinforced lithium silicate, lithium disilicate, and high-translucent zirconia) were ground to the recommended material thickness for single crown restorations and laminated with a 100 μm thick layer of one of three adhesive cements. The disks were fixed to extracted human molars with or without carious lesions of one of three standardized sizes. A total of 240 stacks of cross-sectional scans obtained using an 870-nm SD-OCT with enhanced depth imaging (EDI) were presented to five raters. Diagnostic accuracy was determined by rating the teeth beneath the cemented material as carious or healthy.

RESULTS

Carious samples were distinguished from sound teeth with high diagnostic accuracy, even for early stage caries. Sensitivity (SE) and specificity (SP) pooled over all raters and all materials were 0.9 and 0.97, respectively. When analyzing the effect of the ceramic and cement materials on detection rates, high SE and SP values of >0.96 and >0.91, respectively, were recorded for lithium disilicate, zirconia-reinforced lithium silicate, and high-translucent zirconia irrespective of the cement type. For hybrid and feldspathic ceramics, the cement material was found to have a significant effect on caries detection.

CONCLUSIONS

Given its high diagnostic accuracy, 870-nm SD-OCT with EDI might be useful for the detection of caries beneath restorative materials. The effect of the prescribed ceramic and cement material on optical penetration depth is substantial.

OCT-Based Periodontal Inspection Framework

Periodontal diagnosis requires discovery of the relations among teeth, gingiva (i.e., gums), and alveolar bones, but alveolar bones are inside gingiva and not visible for inspection. Traditional probe examination causes pain, and X-ray based examination is not suited for frequent inspection. This work develops an automatic non-invasive periodontal inspection framework based on gum penetrative Optical Coherence Tomography (OCT), which can be frequently applied without high radiation. We sum up interference responses of all penetration depths for all shooting directions respectively to form the shooting amplitude projection. Because the reaching interference strength decays exponentially with tissues' penetration depth, this projection mainly reveals the responses of the top most gingiva or teeth. Since gingiva and teeth have different air-tissue responses, the gumline, revealing itself as an obvious boundary between teeth and gingiva, is the basis line for periodontal inspection. Our system can also automatically identify regions of gingiva, teeth, and alveolar bones from slices of the cross-sectional volume. Although deep networks can successfully and possibly segment noisy maps, reducing the number of manually labeled maps for training is critical for our framework. In order to enhance the effectiveness and efficiency of training and classification, we adjust Snake segmentation to consider neighboring slices in order to locate those regions possibly containing gingiva-teeth and gingiva-alveolar boundaries. Additionally, we also adapt a truncated direct logarithm based on the Snake-segmented region for intensity quantization to emphasize these boundaries for easier identification. Later, the alveolar-gingiva boundary point directly under the gumline is the desired alveolar sample, and we can measure the distance between the gumline and alveolar line for visualization and direct periodontal inspection. At the end, we experimentally verify our choice in intensity quantization and boundary identification against several other algorithms while applying the framework to locate gumline and alveolar line in vivo data successfully.

Interactive OCT-Based Tooth Scan and Reconstruction

Digital dental reconstruction can be a more efficient and effective mechanism for artificial crown construction and period inspection. However, optical methods cannot reconstruct those portions under gums, and X-ray-based methods have high radiation to limit their applied frequency. Optical coherence tomography (OCT) can harmlessly penetrate gums using low-coherence infrared rays, and thus, this work designs an OCT-based framework for dental reconstruction using optical rectification, fast Fourier transform, volumetric boundary detection, and Poisson surface reconstruction to overcome noisy imaging. Additionally, in order to operate in a patient's mouth, the caliber of the injector is small along with its short penetration depth and effective operation range, and thus, reconstruction requires multiple scans from various directions along with proper alignment. However, flat regions, such as the mesial side of front teeth, may not have enough features for alignment. As a result, we design a scanning order for different types of teeth starting from an area of abundant features for easier alignment while using gyros to track scanned postures for better initial orientations. It is important to provide immediate feedback for each scan, and thus, we accelerate the entire signal processing, boundary detection, and point-cloud alignment using Graphics Processing Units (GPUs) while streamlining the data transfer and GPU computations. Finally, our framework can successfully reconstruct three isolated teeth and a side of one living tooth with comparable precisions against the state-of-art method. Moreover, a user study also verifies the effectiveness of our interactive feedback for efficient and fast clinic scanning.

[Construction of swept source optical coherence tomography imaging system for root canal endoscopy and application in diagnosis of root fractures]

OBJECTIVE

To construct swept source optical coherence tomography (SS-OCT) imaging system for root canal endoscopy, and to evaluate the accuracy of diagnosing artificial root fractures.

METHODS

An ultra-high-speed (40 kHz) swept laser source was developed based on the piezoelectric tuning filter and the Fourier domain mode locking (FDML) swept laser technology (patent number: 200620135940.2). Ultra-miniature gradient index lens technology (patent number: 201320241218.7) was used to create a thin endoscopic probe with a diameter of 0.86 mm for real-time image transmission. The SS-OCT light source had a wavelength of 1 310 nm and a bandwidth of 100 nm. The axial and transverse image resolutions were 15 μm and 25 μm, respectively. Artificial fractures were created on human mandibular premolars with single root and the premolar roots were prepared to 41 horizontal sections (1 mm thick). 27 root sections with fractures (width: 52-284 μm) and 14 the sections without fractures were observed under an optical stereomicroscope with a cold light source as the gold standard. The horizontal root sections were scanned by self-developed SS-OCT imaging system for root canal endoscopy with a central wavelength of 1 310 nm and bandwidth of 100 nm. The data were reconstructed with 30 μm thick slices at an interval of 30 μm. Two observers, a radiologist and an endodontist, were trained and independently evaluated all the reconstructed images blindly. The diagnostic performance of SS-OCT imaging system was calculated, and statistical analysis was performed.

RESULTS

SS-OCT root canal endoscopic imaging system composed of high-speed swept laser source, fiber coupler, endoscopic probe, reference arm and differential detector. Root sections could be scanned by SS-OCT and imaged in realtime at a depth of 1 to 2 mm. The kappa value for interobserver agreement was 0.792, and the intraobserver agreement was 1.000 and 0.709 for two observers respectively. All of 27 fractured root sections and 12 of 14 root sections without fractures were accurately diagnosed while 2 unfractured root sections were misdiagnosed. The sensitivity was 1.000 and the specificity was 0.857 for diagnosis of artificial root fractures by SS-OCT. The positive predictive value (PPV), negative predictive value (NPV) and the overall accuracy rate were 0.931, 1.000 and 0.951 respectively.

CONCLUSION

The swept source optical coherence tomography imaging system for root canal endoscopy is a promising imaging method for observing root fractures．.

Differential phase standard-deviation-based optical coherence tomographic angiography for human retinal imaging in vivo

We present a differential phase standard-deviation (DPSD)-based optical coherence tomographic (OCT) angiography (OCTA) technique to calculate the angiography images of the human retina. The standard deviation was calculated along the depth direction on the differential phase image of two B-scans (from the same position, at different times) to contrast dynamic vascular signals. The performance of a DPSD was verified by both phantom and in vivo experiments. When compared to other OCTA algorithms such as phase variance OCT, speckle variance OCT, and optical microangiography, we showed that a DPSD achieved improved image contrast and higher sensitivity. Furthermore, we also found the improved signal-to-noise ratio and contrast-to-noise ratio of 1.6 dB and 0.5, respectively, in large scanning range images.

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.

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.

Multiple Wavelength Optical Coherence Tomography Assessments for Enhanced Ex Vivo Intra-Cochlear Microstructural Visualization

The precise identification of intra-cochlear microstructures is an essential otorhinolaryngological requirement to diagnose the progression of cochlea related diseases. Thus, we demonstrated an experimental procedure to investigate the most optimal wavelength range, which can enhance the visualization of ex vivo intra-cochlear microstructures using multiple wavelengths (i.e., 860 nm, 1060 nm, and 1300 nm) based optical coherence tomography (OCT) systems. The high-resolution tomograms, volumetric, and quantitative evaluations obtained from Basilar membrane, organ of Corti, and scala vestibule regions revealed complementary comparisons between the aforementioned three distinct wavelengths based OCT systems. Compared to 860 nm and 1300 nm wavelengths, 1060 nm wavelength OCT was discovered to be an appropriate wavelength range verifying the simultaneously obtainable high-resolution and reasonable depth range visualization of intra-cochlear microstructures. Therefore, the implementation of 1060 nm OCT can minimize the necessity of two distinct OCT systems. Moreover, the results suggest that the performed qualitative and quantitative analysis procedure can be used as a powerful tool to explore further anatomical structures of the cochlea for future studies in otorhinolaryngology.

In vivo imaging of human oral hard and soft tissues by polarization-sensitive optical coherence tomography

Since optical coherence tomography (OCT) provides three-dimensional high-resolution images of biological tissue, the benefit of polarization contrast in the field of dentistry is highlighted in this study. Polarization-sensitive OCT (PS OCT) with phase-sensitive recording is used for imaging dental and mucosal tissues in the human oral cavity in vivo. An enhanced polarization contrast of oral structures is reached by analyzing the signals of the co- and crosspolarized channels of the swept source PS OCT system quantitatively with respect to reflectivity, retardation, optic axis orientation, and depolarization. The calculation of these polarization parameters enables a high tissue-specific contrast imaging for the detailed physical interpretation of human oral hard and soft tissues. For the proof-of-principle, imaging of composite restorations and mineralization defects at premolars as well as gingival, lingual, and labial oral mucosa was performed in vivo within the anterior oral cavity. The achieved contrast-enhanced results of the investigated human oral tissues by means of polarization-sensitive imaging are evaluated by the comparison with conventional intensity-based OCT.

Dynamic measurement of the optical properties of bovine enamel demineralization models using four-dimensional optical coherence tomography

Dental enamel mineral loss is multifactorial and is consequently explored using a variety of in vitro models. Important factors include the presence of acidic pH and its specific ionic composition, which can both influence lesion characteristics. Optical coherence tomography (OCT) has been demonstrated as a promising tool for studying dental enamel demineralization. However, OCT-based characterization and comparison of demineralization model dynamics are challenging without a consistent experimental environment. Therefore, an automated four-dimensional OCT system was integrated with a multispecimen flow cell to measure and compare the optical properties of subsurface enamel demineralization in different models. This configuration was entirely automated, thus mitigating any need to disturb the specimens and ensuring spatial registration of OCT image volumes at multiple time points. Twelve bovine enamel disks were divided equally among three model groups. The model demineralization solutions were citric acid (pH 3.8), acetic acid (pH 4.0), and acetic acid with added calcium and phosphate (pH 4.4). Bovine specimens were exposed to the solution continuously for 48 h. Three-dimensional OCT data were obtained automatically from each specimen at a minimum of 1-h intervals from the same location within each specimen. Lesion dynamics were measured in terms of the depth below the surface to which the lesion extended and the attenuation coefficient. The net loss of surface enamel was also measured for comparison. Similarities between the dynamics of each model were observed, although there were also distinct characteristic differences. Notably, the attenuation coefficients showed a systematic offset and temporal shift with respect to the different models. Furthermore, the lesion depth curves displayed a discontinuous increase several hours after the initial acid challenge. This work demonstrated the capability of OCT to distinguish between different enamel demineralization models by making dynamic quantitative measurements of lesion properties. This has important implications for future applications in clinical dentistry.

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

INTRODUCTION

Radiographic methods have poor sensitivity for occlusal lesions and by the time the lesions are radiolucent they have typically progressed deep into the dentin. New more sensitive imaging methods are needed to detect occlusal lesions. In this study, cross-polarization optical coherence tomography (CP-OCT) and near-IR imaging were used to image questionable occlusal lesions (QOC's) that were not visible on radiographs but had been scheduled for restoration on 30 test subjects.

METHODS

Near-IR reflectance and transillumination probes incorporating a high definition InGaAs camera and near-IR broadband light sources were used to acquire images of the lesions before restoration. The reflectance probe utilized cross-polarization and operated at wavelengths from 1,500 to 1,700 nm where there is an increase in water absorption for higher contrast. The transillumination probe was operated at 1,300 nm where the transparency of enamel is highest. Tomographic images (6 × 6 × 7 mm³ ) of the lesions were acquired using a high-speed swept-source CP-OCT system operating at 1,300 nm before and after removal of the suspected lesion.

RESULTS

Near-IR reflectance imaging at 1,500-1,700 nm yielded significantly higher contrast (P < 0.05) of the demineralization in the occlusal grooves compared with visible reflectance imaging. Stains in the occlusal grooves greatly reduced the lesion contrast in the visible range yielding negative values. Only half of the 26 lesions analyzed showed the characteristic surface demineralization and increased reflectivity below the dentinal-enamel junction (DEJ) in 3D OCT images indicative of penetration of the lesion into the dentin.

CONCLUSION

This study demonstrates that near-IR imaging methods have great potential for improving the early diagnosis of occlusal lesions. Lasers Surg. Med. 49:215-224, 2017. © 2017 Wiley Periodicals, Inc.

Synergistic effect of fluoride and laser irradiation for the inhibition of the demineralization of dental enamel

Both laser irradiation and fluoride treatment alone are known to provide increased resistance to acid dissolution. CO₂ lasers tuned to a wavelength of 9.3 μm can be used to efficiently convert the carbonated hydroxyapatite of enamel to a much more acid resistant purer phase hydroxyapatite (HAP). Further studies have shown that fluoride application to HAP yields fluoroapatite (FAP) which is even more resistant against acid dissolution. Previous studies show that CO₂ lasers and fluoride treatments interact synergistically to provide significantly higher protection than either method alone, but the mechanism of interaction has not been elucidated. We recently observed the formation of microcracks or a "crazed" zone in the irradiated region that is resistant to demineralization using high-resolution microscopy. The microcracks are formed due to the slight contraction of enamel due to transformation of carbonated hydroxyapatite to the more acid resistant pure phase hydroxyapatite (HAP) that has a smaller lattice. In this study, we test the hypothesis that these small cracks will provide greater adhesion for topical fluoride for greater protection against acid demineralization.

Influence of a pulsed CO2 laser operating at 9.4 μm on the surface morphology, reflectivity, and acid resistance of dental enamel below the threshold for melting

Below the threshold for laser ablation, the mineral phase of enamel is converted into a purer phase hydroxyapatite with increased acid resistance. Studies suggest the possibility of achieving the conversion without visible surface alteration. In this study, changes in the surface morphology, reflectivity, and acid resistance were monitored with varying irradiation intensity. Bovine enamel specimens were irradiated using a CO 2 laser operating at 9.4 ?? ? m with a Gaussian spatial beam profile—1.6 to 3.1 mm in diameter. After laser treatment, samples were subjected to demineralization to simulate the acidic intraoral conditions of dental decay. The resulting demineralization and erosion were assessed using polarization-sensitive optical coherence tomography, three-dimensional digital microscopy, and polarized light microscopy. Distinct changes in the surface morphology and the degree of inhibition were found within the laser-treated area in accordance with the laser intensity profile. Subtle visual changes were noted below the melting point for enamel that appear to correspond to thresholds for denaturation of the organic phase and thermal decomposition of the mineral phase. There was significant protection from laser irradiation in areas in which the reflectivity was not increased significantly, suggesting that aesthetically sensitive areas of the tooth can be treated for caries prevention.

Longitudinal correlation of 3D OCT to detect early stage erosion in bovine enamel

Erosive tissue-loss in dental enamel is of significant clinical concern because the net loss of enamel is irreversible, however, initial erosion is reversible. Micro-hardness testing is a standard method for measuring initial erosion, but its invasive nature has led to the investigation of alternative measurement techniques. Optical coherence tomography (OCT) is an attractive alternative because of its ability to non-invasively image three-dimensional volumes. In this study, a four-dimensional OCT system is used to longitudinally measure bovine enamel undergoing a continuous erosive challenge. A new method of analyzing 3D OCT volumes is introduced that compares intensity projections of the specimen surface by calculating the slope of a linear regression line between corresponding pixel intensities and the associated correlation coefficient. The OCT correlation measurements are compared to micro-hardness data and found to exhibit a linear relationship. The results show that this method is a sensitive technique for the investigation of the formation of early stage erosive lesions.

Refractive index variance of cells and tissues measured by quantitative phase imaging

The refractive index distribution of cells and tissues governs their interaction with light and can report on morphological modifications associated with disease. Through intensity-based measurements, refractive index information can be extracted only via scattering models that approximate light propagation. As a result, current knowledge of refractive index distributions across various tissues and cell types remains limited. Here we use quantitative phase imaging and the statistical dispersion relation (SDR) to extract information about the refractive index variance in a variety of specimens. Due to the phase-resolved measurement in three-dimensions, our approach yields refractive index results without prior knowledge about the tissue thickness. With the recent progress in quantitative phase imaging systems, we anticipate that using SDR will become routine in assessing tissue optical properties.

Bio-Photonic Detection and Quantitative Evaluation Method for the Progression of Dental Caries Using Optical Frequency-Domain Imaging Method

The initial detection of dental caries is an essential biomedical requirement to barricade the progression of caries and tooth demineralization. The objective of this study is to introduce an optical frequency-domain imaging technique based quantitative evaluation method to calculate the volume and thickness of enamel residual, and a quantification method was developed to evaluate the total intensity fluctuation in depth direction owing to carious lesions, which can be favorable to identify the progression of dental caries in advance. The cross-sectional images of the ex vivo tooth samples were acquired using 1.3 μm spectral domain optical coherence tomography system (SD-OCT). Moreover, the advantages of the proposed method over the conventional dental inspection methods were compared to highlight the potential capability of OCT. As a consequence, the threshold parameters obtained through the developed method can be used as an efficient investigating technique for the initial detection of demineralization.

In Vivo Detection of the Effect of Electroacupuncture on "Zusanli" Acupoint in Rats with Adjuvant-Induced Arthritis through Optical Coherence Tomography

This study aimed to investigate the effect of electroacupuncture (EA) treatment through optical coherence tomography (OCT) in vivo on rats with adjuvant-induced arthritis. OCT images were obtained from the ankle of the right hind paws of the rats in control, model, and EA groups before modelling and 1 day, 8 days, 15 days, 22 days, and 29 days after modelling. Results demonstrated that the OCT signal of the ankle of the right hind paws of the rats was indistinct compared to 1 day after modelling and before modelling in the EA group. In the EA group, the light averaged attenuation coefficients of the ankle tissues decreased as treatment duration was prolonged after EA was administered (3.43, 2.96, 2.61, 2.42, and 2.29 mm⁻¹, resp.). There was a significant difference in attenuation coefficient decrease between the 29th d and the 1st d for EA group compared with control group (P < 0.01). This condition indicated that the light absorption of the ankle of the treated rats in the EA group decreased. Therefore, OCT can be used to monitor the effect of treatment on rats with arthritis in vivo.

Enamel Thickness Determination by Optical Coherence Tomography: In vitro Validation

Optical coherence tomography (OCT) has been introduced in dentistry as a nondestructive diagnostic imaging tool that does not utilize ionizing radiation. This study investigated the agreement between polarization-sensitive OCT (PS-OCT), microcomputed tomography (μ-CT), and histology for enamel thickness measurements. Human enamel samples were prepared and evaluated with μ-CT and PS-OCT and then sectioned and observed via digital transversal light microscopy. For all methods, a standard transversal section (b-scan) in each sample was selected, and the enamel thickness was measured at three predetermined positions using ImageJ analysis software. The results revealed significant high agreement between all tested methods, indicating the potential of PS-OCT as a clinical tool to effectively measure enamel thickness.

Clinical monitoring of smooth surface enamel lesions using CP-OCT during nonsurgical intervention

INTRODUCTION

Studies have shown that cross-polarization optical coherence tomography (CP-OCT) can be used to image the internal structure of carious lesions in vivo. The objective of this study was to show that CP-OCT can be used to monitor changes in the internal structure of early active carious lesions on smooth surfaces during non-surgical intervention with fluoride.

METHODS

Lesions on the smooth surfaces of teeth were imaged using CP-OCT on 17 test subjects. Lesion structural changes were monitored during fluoride varnish application at 6-week intervals for 30 weeks. The lesion depth (L_d ), integrated reflectivity (ΔR), and surface zone thickness (S_z ) were monitored.

RESULTS

A distinct transparent surface zone that may be indicative of lesion arrestment was visible in CP-OCT images on 62/63 lesions before application of fluoride varnish. The lesion depth and internal structure were resolved for all the lesions. The overall change in the mean values for L_d , ΔR, and S_z for all the lesions was minimal and was not significant during the study (P > 0.05). Only 5/63 lesions manifested a significant increase in S_z during intervention.

CONCLUSION

Even though it appears that most of the lesions manifested little change with fluoride varnish application in the 30 weeks of the study, CP-OCT was able to measure the depth and internal structure of all the lesions including the thickness of the important transparent surface zone located at the surface of the lesions, indicating that CP-OCT is ideally suited for monitoring lesion severity in vivo. Lasers Surg. Med. 48:915-923, 2016. © 2016 Wiley Periodicals, Inc.

Assessment of simulated lesions on primary teeth with near-infrared imaging

Previous studies have demonstrated that the structural changes on enamel due to demineralization and remineralization can be exploited through optical imaging methods such as QLF, thermal and NIR imaging. The purpose of this study is to investigate whether PS-OCT and NIR reflectance imaging can be utilized to assess lesion structure in artificial enamel lesions on the smooth surfaces of primary teeth exposed to fluoride. The smooth coronal surfaces of primary teeth (n=25) were divided into 4 windows: sound, demineralization, demineralization with remineralization and APF with demineralization. Windows were treated with either acidulated phosphate fluoride (APF) for 1 minute, a demineralization solution for 4 days, and/or an acidic remineralization solution for 12 days. The samples were imaged using PS-OCT, QLF and NIR reflectance at 1400-1700 nm wavelengths. This study demonstrated that both PS-OCT and NIR reflectance imaging were suitable for assessing lesion structure in the smooth surfaces of primary dentition.

Evaluation of enamel surface modification using PS-OCT after laser treatment to increase resistance to demineralization

At laser intensities below ablation, carbonated hydroxyapatite in enamel is converted into a purer phase hydroxyapatite with increased acid resistance. Previous studies suggested the possibility of achieving the conversion without surface modification. This study attempts to evaluate the thresholds for the modification without additional changes in physical and optical properties of the enamel. Bovine specimens were irradiated using an RF-excited CO₂ laser operating at 9.4-µm with a pulse duration of 26-µs, pulse repetition rates of 100-1000 Hz, with a Gaussian spatial beam profile - 1.4 mm in diameter. After laser treatment, the samples were subjected to acid demineralization for 48 hours to simulate acidic intraoral conditions of a caries attack. The resulting demineralization and erosion were assessed using polarization sensitive OCT (PS-OCT) and 3D digital microscopy. The images from digital microscopy demonstrated a clear delineation between laser protected zones without visual changes and zones with higher levels of demineralization and erosion. Distinct changes in the surface morphology were found within the laser treated area in accordance with the Gaussian spatial beam profile. There was significant protection from the laser in areas that were not visually altered.

Enhancement of OCT images with vinyl polysiloxane (VPS)

Several studies have shown that optical coherence tomography (OCT) can be used to measure the remaining enamel thickness and detect the location of subsurface lesions hidden under the sound enamel. Moreover studies have shown that high refractive index liquids can be used to improve the visibility of subsurface lesions in OCT images. In this study, we demonstrate that vinyl polysiloxane (VPS) impression materials which are routinely used in dentistry can be used to enhance the detection of dentinal lesions on tooth occlusal surfaces. Lesion presence was confirmed with polarized light microscopy and microradiography.

Assessment of curing behavior of light-activated dental composites using intensity correlation based multiple reference optical coherence tomography

BACKGROUND AND OBJECTIVES

Monitoring the curing kinetics of light-activated resin is a key area of research. These resins are used in restorative applications and particularly in dental applications. They can undergo volumetric shrinkage due to poor control of the depth dependent curing process, modulated by the intensity and duration of the curing light source. This often results in the formation of marginal gaps, causing pain and damage to the restoration site. In this study, we demonstrate the capabilities of a correlation method applied using a multiple references optical coherence tomography (MR-OCT) architecture to monitor the curing of the resin.

STUDY DESIGN/MATERIALS AND METHODS

A MR-OCT system is used in this study to monitor the curing of the resin. The system operates at the center wavelength of 1310 nm with an A-scan rate of 1200 A-scans per second. The axial and lateral resolution of the system is ∼13 μm and ∼27 μm. The method to determine the intensity correlation between adjacent B-frames is based on the Pearson correlation coefficient for a region of interest. Calculating the correlation coefficient for multiple B-frames related to the first B-frame at regular spaced time points, shows for a noncured resin a reduction of the correlation coefficient over time due to Brownian motion. The time constant of the reduction of the correlation value is a measure for the progress of the polymerization during LED light irradiation of the resin. The proposed approach is potentially a low-cost, powerful and unique optical imaging modality for measuring the curing behavior of dental resin and other resins, coatings, and adhesives in medical and industrial applications.

RESULTS

To demonstrate the proposed method to monitor the curing process, a light-activated resin composite from GRADIA DIRECT ANTERIOR (GC Corporation, Japan) is studied. The curing time of resin was measured and monitored as a function of depth. The correlation coefficient method is highly sensitive to Brownian motion. The process of curing results in a change in intensity as measured by the MR-OCT signal and hence can be monitored using this method.

CONCLUSIONS

These results show that MR-OCT has the potential to measure the curing time and monitor the curing process as a function of depth. Moreover, MR-OCT as a product has potential to be compact, low-cost and to fit into a smartphone. Using such a device for monitoring the curing of the resin will be suitable for dentists in stationary and mobile clinical settings.

Detection and proportion of very early dental caries in independent living older adults

BACKGROUND AND OBJECTIVES

Dental caries is an important healthcare challenge in adults over 65 years of age. Integration of oral health screening into non-dental primary care practice may improve access to preventive dental care for vulnerable populations such as the elderly. Such integration would require easy, fast, and accurate early caries detection tools. Primary goal of this study was to evaluate the diagnostic performance of optical coherence tomography (OCT) imaging for detecting very early caries in the elderly living in community-based settings. The International Caries Detection and Assessment System (ICDAS) served as gold standard. Secondary goal of this study was to provide baseline prevalence data of very early caries lesions in independent living adults aged 65+ years.

MATERIALS AND METHODS

Seventy-two subjects were recruited from three sites in Southern California: a retirement community, a senior health fair, and a convalescent hospital. Clinical examination was performed using the ICDAS visual criteria and this was followed by OCT imaging. The two-dimensional OCT images (B-scan) were analyzed with simple software. Locations with a log of back-scattered light intensity (BSLI) below 2.9 were scored as sound, and areas equaling or exceeding 2.9 BSLI were considered carious. Diagnostic performance of OCT imaging was compared with ICDAS score.

RESULTS

OCT-based diagnosis demonstrated very good sensitivity (95.1%) and good specificity (85.8%). 54.7% of dentate subjects had at least one tooth with very early coronal caries.

CONCLUSIONS

Early coronal decay is prevalent in the unrestored pits and fissures of coronal surfaces of teeth in independent living adults aged 65+ years. Though OCT imaging coupled with a simple diagnostic algorithm can accurately detect areas of very early caries in community-based settings, existing devices are expensive and not well-suited for use by non-dental health care providers. Simple, inexpensive, fast, and accurate tools for early caries detection by field health care providers working in non-traditional settings are urgently needed to support inter-professional dental health management.

Functional optical coherence tomography: principles and progress

In the past decade, several functional extensions of optical coherence tomography (OCT) have emerged, and this review highlights key advances in instrumentation, theoretical analysis, signal processing and clinical application of these extensions. We review five principal extensions: Doppler OCT (DOCT), polarization-sensitive OCT (PS-OCT), optical coherence elastography (OCE), spectroscopic OCT (SOCT), and molecular imaging OCT. The former three have been further developed with studies in both ex vivo and in vivo human tissues. This review emphasizes the newer techniques of SOCT and molecular imaging OCT, which show excellent potential for clinical application but have yet to be well reviewed in the literature. SOCT elucidates tissue characteristics, such as oxygenation and carcinogenesis, by detecting wavelength-dependent absorption and scattering of light in tissues. While SOCT measures endogenous biochemical distributions, molecular imaging OCT detects exogenous molecular contrast agents. These newer advances in functional OCT broaden the potential clinical application of OCT by providing novel ways to understand tissue activity that cannot be accomplished by other current imaging methodologies.

Application of Optical Coherence Tomography (OCT) for Diagnosis of Caries, Cracks, and Defects of Restorations

Optical coherence tomography (OCT) is a noninvasive technique providing cross-sectional images of a tooth structure. This review describes the use of OCT for detecting dental caries, tooth fractures, and interfacial gaps in intraoral restorations. OCT can be a reliable and an accurate method and a safer alternative to X-ray radiography.

Assessment of remineralization via measurement of dehydration rates with thermal and near-IR reflectance imaging

OBJECTIVES

Previous studies have demonstrated that the optical changes due to the loss of water from porous lesions can be exploited to assess lesion severity with QLF, thermal and near-IR imaging. Since arrested lesions are less permeable to water due to the highly mineralized surface layer, changes in the rate of water loss can be related to changes in lesion structure. The purpose of this study was to investigate whether the rate of water loss correlates with the degree of remineralization and whether that rate can be measured using thermal and near-IR reflectance imaging.

METHODS

Artificial bovine enamel lesions (n=30) were prepared by immersion in a demineralization solution for either 8 and 24 h and they were subsequently placed in an acidic remineralization solution for different periods. The samples were dehydrated using an air spray for 30s and surfaces were imaged using a thermal camera and an InGaAs camera at 1300-1700 nm wavelengths.

RESULTS

The area enclosed by the time-temperature curve, ΔQ, from thermal imaging showed significant differences (P<0.05) between the lesion window and other windows. Near-IR reflectance intensity differences, ΔI, before and after dehydration decreased with longer periods of remineralization. Only near-IR reflectance imaging was capable of detecting significant differences (P<0.05) between the different periods of remineralization.

CONCLUSIONS

This study demonstrated that both thermal and near-IR reflectance imaging were suitable for the detection of remineralization in simulated caries lesions and near-IR wavelengths longer than 1400 nm are well suited for the assessment of remineralization.

Enhanced detection of dentinal lesions in OCT images using the RKT transformation

Several studies have shown that optical coherence tomography (OCT) can be used to measure the remaining enamel thickness and detect the location of subsurface lesions hidden under the sound enamel. The purpose of this study was to develop algorithms to enhance the visibility of subsurface structures such as hidden occlusal lesions and the dentinal-enamel junction. Extracted teeth with natural occlusal lesions were imaged with OCT with and without added high index fluids. A Rotating Kernel Transformation (RKT) nonlinear image processing filter was applied to PS-OCT images to enhance the visibility of the subsurface lesions under the sound enamel. The filter significantly increased (P<0.05) the visibility of the subsurface lesions.

Use of 2D images of depth and integrated reflectivity to represent the severity of demineralization in cross-polarization optical coherence tomography

Several studies have demonstrated the potential of cross-polarization optical coherence tomography (CP-OCT) to quantify the severity of early caries lesions (tooth decay) on tooth surfaces. The purpose of this study is to show that 2D images of the lesion depth and the integrated reflectivity can be used to accurately represent the severity of early lesions. Simulated early lesions of varying severity were produced on tooth samples using simulated lesion models. Methods were developed to convert the 3D CP-OCT images of the samples to 2D images of the lesion depth and lesion integrated reflectivity. Calculated lesion depths from OCT were compared with lesion depths measured from histological sections examined using polarized light microscopy. The 2D images of the lesion depth and integrated reflectivity are well suited for visualization of early demineralization.

Depth-encoded all-fiber swept source polarization sensitive OCT

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of conventional OCT and can assess depth-resolved tissue birefringence in addition to intensity. Most existing PS-OCT systems are relatively complex and their clinical translation remains difficult. We present a simple and robust all-fiber PS-OCT system based on swept source technology and polarization depth-encoding. Polarization multiplexing was achieved using a polarization maintaining fiber. Polarization sensitive signals were detected using fiber based polarization beam splitters and polarization controllers were used to remove the polarization ambiguity. A simplified post-processing algorithm was proposed for speckle noise reduction relaxing the demand for phase stability. We demonstrated systems design for both ophthalmic and catheter-based PS-OCT. For ophthalmic imaging, we used an optical clock frequency doubling method to extend the imaging range of a commercially available short cavity light source to improve polarization depth-encoding. For catheter based imaging, we demonstrated 200 kHz PS-OCT imaging using a MEMS-tunable vertical cavity surface emitting laser (VCSEL) and a high speed micromotor imaging catheter. The system was demonstrated in human retina, finger and lip imaging, as well as ex vivo swine esophagus and cardiovascular imaging. The all-fiber PS-OCT is easier to implement and maintain compared to previous PS-OCT systems and can be more easily translated to clinical applications due to its robust design.

Automated assessment of the remineralization of artificial enamel lesions with polarization-sensitive optical coherence tomography

Accurate measurement of the highly mineralized transparent surface layer that forms on caries lesions is important for diagnosis of the lesion activity because chemical intervention can slow or reverse the caries process via remineralization. Previous in-vitro and in-vivo studies have demonstrated that polarization-sensitive optical coherence tomography (PS-OCT) can nondestructively image the subsurface lesion structure and the highly mineralized transparent surface zone of caries lesions. The purpose of this study was to develop an approach to automatically process 3-dimensional PS-OCT images and to accurately assess the remineralization process in simulated enamel lesions. Artificial enamel lesions were prepared on twenty bovine enamel blocks using two models to produce varying degree of demineralization and remineralization. The thickness of the transparent surface layer and the integrated reflectivity of the subsurface lesion were measured using PS-OCT. The automated transparent surface layer detection algorithm was able to successfully detect the transparent surface layers with high sensitivity ( = 0.92) and high specificity ( = 0.97). The estimated thickness of the transparent surface layer showed a strong correlation with polarized light microscopy (PLM) measurements of all regions (R(2) = 0.90). The integrated reflectivity, ΔR, and the integrated mineral loss, ΔZ, showed a moderate correlation (R(2) = 0.32). This study demonstrates that PS-OCT can automatically measure the changes in artificial enamel lesion structure and severity upon exposure to remineralization solutions.

A method for monitoring enamel erosion using laser irradiated surfaces and optical coherence tomography

INTRODUCTION

Since optical coherence tomography (OCT) is well suited for measuring small dimensional changes on tooth surfaces, OCT has great potential for monitoring tooth erosion. Previous studies have shown that enamel areas ablated by a carbon dioxide laser manifested lower rates of erosion compared to the non-ablated areas. The purpose of this study was to develop a model to monitor erosion in vitro that could potentially be used in vivo.

METHODS

Thirteen bovine enamel blocks were used in this in vitro study. Each 10 mm × 2 mm block was partitioned into five regions, the central region was unprotected, the adjacent windows were irradiated by a CO2 laser operating at 9.3 µm with a fluence of 2.4 J/cm(2) , and the outermost windows were coated with acid resistant varnish. The samples were exposed to a pH cycling regimen that caused both erosion and subsurface demineralization for 2, 4 and 6 days. The surfaces were scanned using a time-domain polarization sensitive optical coherence tomography (PS-OCT) system and the degree of surface loss (erosion) and the integrated reflectivity with lesion depth was calculated for each window.

RESULTS

There was a large and significant reduction in the depth of surface loss (erosion) and the severity of demineralization in the areas irradiated by the laser.

CONCLUSION

Irradiation of the enamel surface with a pulsed carbon dioxide laser at sub-ablative intensities results in significant inhibition of erosion and demineralization under the acid challenge employed in this study. In addition, these results suggest that it may be feasible to modify regions of the enamel surface using the laser to serve as reference marks to monitor the rate of erosion in vivo.

An update on optical coherence tomography in dentistry

An update and overview of the use of optical coherence tomography (OCT) in dentistry is described. Specific aspects discussed include the evolution of the technology and the basic process of light beam interference used to obtain OCT images. In addition, aspects of the optical properties of dentine and enamel and the range of current diagnostic applications of OCT in dentistry are reviewed.

CLINICAL RELEVANCE

The technique of optical coherence tomography is considered to be significant since the technology involved allows imaging using light to around 2-3 mm in teeth and can, for example, allow the extent and progression of carious lesions to be determined.