In vivo OCT imaging of hard and soft tissue of the oral cavity

A wearable triboelectric impedance tomography system for noninvasive and dynamic imaging of biological tissues

Tissue imaging is usually captured by hospital-based nuclear magnetic resonance. Here, we present a wearable triboelectric impedance tomography (TIT) system for noninvasive imaging of various biological tissues. The imaging mechanism relies on the obtained impedance information from the different soft human tissues. A high-precision signal source is designed on the basis of a composite triboelectric nanogenerator, which exhibits a minimal total harmonic distortion of 0.03% and a peak output signal-to-noise ratio up to 120 decibels. The current density injected into human skin is around 79.58 milliamperes per square meter, far below the safety threshold for medical devices. The TIT system achieves time-resolved tomography of human limbs' soft tissues, and many appealing functions can be realized by using this wearable system, including the observation of muscle movement, the motion intention recognition, and the identification of pathological changes of soft tissue. Hence, this TIT system with excellent biocompatibility can be integrated with various devices, such as medical-assistive exoskeletons and smart protective suit.

The Effect of Cryotherapy on Buccal Blood Vessels Evaluated by Optical Coherence Tomography Angiography: A Pilot Study

While cryotherapy is one of the traditional ways to reduce postoperative complications in maxillofacial surgery, the cooling degree is not regulated in most cases and the achieved effect is not properly controlled. Therefore, to develop optimal cooling modes, we propose to study the buccal vascular response to cooling, which has not been previously shown. To evaluate the effect of cooling, we analyzed vessel networks using optical coherence tomography angiography (OCT-A). The cheek vessels were OCT-A monitored using cooling by an ice bag/cooling mask. We found the advantages of using a cooling mask over an ice bag consist of a statistically significant decrease in the perfused vessel density (PVD) of the papillary layer at the oral mucosa. The absence of the reticular layer vessel reaction to any type of cooling was noted. We argue for the necessity to develop optimal modes of cryotherapy, which will contribute to blood perfusion reduction and reduction of PVD recovery.

Quantitative assessment of the oral microvasculature using optical coherence tomography angiography

Introduction

Early diagnosis of oral squamous cell carcinoma can greatly improve treatment success rate and patient survival. Although Optical Coherence Tomography (OCT) based Angiography (OCTA) is a promising in vivo technique in oral imaging, there is a need for objective assessment of oral microvasculature.

Methods

This study aimed to demonstrate a comprehensive methodology of quantitative assessing OCTA intraoral scanning results to provide measurable, reproducible data and to avoid subjective visual interpretations. Data were collected from 37 healthy subjects in total across four intraoral sites-buccal mucosa (n = 32), labial mucosa (n = 24), floor of the mouth (n = 13), and hard palate (n = 8)-using a non-invasive swept-source OCT system. Four quantitative metrics-vessel area density, vessel skeleton density, vessel diameter index, and a newly proposed weighted Tortuosity Index-were used to assess OCTA images in oral applications.

Results

The quadruple quantitative assessment's repeatability was evaluated to be reliable. Analysis of a benign ulcer case revealed differences in these metrics compared to healthy cases.

Discussion/Conclusion

In conclusion, we demonstrated a comprehensive method to quantify microvasculature in the oral cavity, showing considerable promise for early diagnosis and clinical management of oral diseases.

Dual-modal Photoacoustic and Ultrasound Imaging: from preclinical to clinical applications

Photoacoustic imaging is a novel biomedical imaging modality that has emerged over the recent decades. Due to the conversion of optical energy into the acoustic wave, photoacoustic imaging offers high-resolution imaging in depth beyond the optical diffusion limit. Photoacoustic imaging is frequently used in conjunction with ultrasound as a hybrid modality. The combination enables the acquisition of both optical and acoustic contrasts of tissue, providing functional, structural, molecular, and vascular information within the same field of view. In this review, we first described the principles of various photoacoustic and ultrasound imaging techniques and then classified the dual-modal imaging systems based on their preclinical and clinical imaging applications. The advantages of dual-modal imaging were thoroughly analyzed. Finally, the review ends with a critical discussion of existing developments and a look toward the future.

Potential Application of Non-Invasive Optical Imaging Methods in Orthodontic Diagnosis

During orthodontic treatment, the early diagnosis of microscopic changes in soft and hard tissues, including periodontal tissue, is very important to prevent iatrogenic side effects like root resorption and periodontal diseases. Cervical periodontal tissue is the most critical area that reacts first to mal-habits or orthodontic forces, and it is also the place where bacteria deposits in the early stage of periodontal diseases. The early diagnosis of hard tissue changes, such as demineralization, is also very important in maintaining a patient's health during orthodontic treatment. Many diagnostic devices, including radiographic equipment and intra-oral scanners, are helpful in diagnosing these problems, but have certain limitations in invasiveness and precision. The purpose of this study is to verify the possible utilities of non-invasive diagnostic devices in the orthodontic field that can compensate for these limitations. For this, non-invasive optical diagnostic devices, including optical coherence tomography and optical Doppler tomography, were used in vivo with animal and human examination for hard and soft tissues. These devices can provide real-time three-dimensional images at the histological scale. The results of this study verified these devices can be used in clinical practice during orthodontic treatment and introduced a new diagnostic paradigm differentiating microstructural changes in tissues in orthodontic diagnosis.

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.

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).

Passively scanned, single-fiber optical coherence tomography probes for gastrointestinal devices

BACKGROUND/OBJECTIVES

Optical coherence tomography (OCT) uses low coherence interferometry to obtain depth-resolved tissue reflectivity profiles (M-mode) and transverse beam scanning to create images of two-dimensional tissue morphology (B-mode). Endoscopic OCT imaging probes typically employ proximal or distal mechanical beam scanning mechanisms that increase cost, complexity, and size. Here, we demonstrate in the gastrointestinal (GI) tracts of unsedated human patients, that a passive, single-fiber probe can be used to guide device placement, conduct device-tissue physical contact sensing, and obtain two-dimensional OCT images via M-to-B-mode conversion.

MATERIALS AND METHODS

We designed and developed ultrasmall, manually scannable, side- and forward-viewing single fiber-optic probes that can capture M-mode OCT data. Side-viewing M-mode OCT probes were incorporated into brush biopsy devices designed to harvest the microbiome and forward-viewing M-mode OCT probes were integrated into devices that measure intestinal potential difference (IPD). The M-mode OCT probe-coupled devices were utilized in the GI tract in six unsedated patients in vivo. M-mode data were converted into B-mode images using an M-to-B-mode conversion algorithm. The effectiveness of physical contact sensing by the M-mode OCT probes was assessed by comparing the variances of the IPD values when the probe was in physical contact with the tissue versus when it was not. The capacity of forward- and side-viewing M-mode OCT probes to produce high-quality B-mode images was compared by computing the percentages of the M-to-B-mode images that showed close contact between the probe and the luminal surface. Passively scanned M-to-B-mode images were qualitatively compared to B-mode images obtained by mechanical scanning OCT tethered capsule endomicroscopy (TCE) imaging devices.

RESULTS

The incorporation of M-mode OCT probes in these nonendoscopic GI devices safely and effectively enabled M-mode OCT imaging, facilitating real-time device placement guidance and contact sensing in vivo. Results showed that M-mode OCT contact sensing improved the variance of IPD measurements threefold and side-viewing probes increased M-to-B-mode image visibility by 10%. Images of the esophagus, stomach, and duodenum generated by the passively scanned probes and M-to-B-mode conversion were qualitatively superior to B-mode images obtained by mechanically scanning OCT TCE devices.

CONCLUSION

These results show that passive, single optical fiber OCT probes can be effectively utilized for nonendoscopic device placement guidance, device contact sensing, and two-dimensional morphologic imaging in the human GI tract in vivo. Due to their small size, lower cost, and reduced complexity, these M-mode OCT probes may provide an easier avenue for the incorporation of OCT functionality into endoscopic/nonendoscopic devices.

Recent Advances in the Diagnosis of Enamel Cracks: A Narrative Review

Cracked teeth can pose a diagnostic dilemma for a clinician as they can mimic several other conditions. The constant physiological stress along with any pathological strain like trauma or iatrogenic causes can lead to the development of microcracks in the teeth. Constant exposure to immense stress can cause the progression of these often-undiagnosed tooth cracks to cause tooth fractures. This review aims to outline the etiology of tooth cracks, their classification, and recent advances in the diagnosis of enamel cracks. Diagnosing a cracked tooth can be an arduous task as symptoms differ according to the location and extension of the incomplete fracture. Early detection is critical because restorative treatment can prevent fracture propagation, microleakage, pulpal or periodontal tissue involvement, and catastrophic cusp failure. Older methods of crack detection are not sensitive or specific. They include clinical examination, visual inspection, exploratory excavation, and percussion test. The dye test used blue or gentian violet stains to highlight fracture lines. Modern methods include transillumination, optical coherence tomography Swept-Source Optical Coherence Tomography (SSOCT), near-infrared imaging, ultrasonic system, infrared thermography, and near-infrared laser. These methods appear to be more efficacious than traditional clinical dental imaging techniques in detecting longitudinal tooth cracks. Clinically distinguishing between the various types of cracks can be difficult with patient-reported signs and symptoms varying according to the location and extension of the incomplete fracture. Cracks are more common in restored teeth. Technological advances such as transillumination allow for early detection and enhanced prognosis.

Noninvasive Imaging Methods to Improve the Diagnosis of Oral Carcinoma and Its Precursors: State of the Art and Proposal of a Three-Step Diagnostic Process

Simple Summary

Oral squamous cell carcinoma (OSCC) accounts for 90–95% of malignant tumors of the lip and oral cavity and is associated with high mortality in the advanced stages. Early diagnosis is a challenge for oral pathologists and dentists, due to the ambiguous appearance of early OSCC, which is often misdiagnosed, mistreated, and associated with diagnostic delay. The gold standards for OSCC diagnosis are biopsy and histopathological assessment, but these procedures are invasive and time-consuming. Adjunctive noninvasive techniques allow the definition of the malignant features of a suspicious lesion in real time and noninvasively, thus improving the diagnostic procedure. The present review aimed to focus on some of the main promising noninvasive imaging techniques, to highlight their perspective adoption in a three-step diagnosis, which is idealistically faster and better, as well as enables the patient’s compliance.

Abstract

Oral squamous cell carcinoma (OSCC) is the most prevalent form of cancer of lips and oral cavity, and its diagnostic delay, caused by misdiagnosis at the early stages, is responsible for high mortality ratios. Biopsy and histopathological assessment are the gold standards for OSCC diagnosis, but they are time-consuming, invasive, and do not always enable the patient’s compliance, mainly in cases of follow-up with the need for more biopsies. The use of adjunctive noninvasive imaging techniques improves the diagnostic approach, making it faster and better accepted by patients. The present review aims to focus on the most consolidated diagnostic techniques, such as vital staining and tissue autofluorescence, and to report the potential role of some of the most promising innovative techniques, such as narrow-band imaging, high-frequency ultrasounds, optical coherence tomography, and in vivo confocal microscopy. According to their contribution to OSCC diagnosis, an ideal three-step diagnostic procedure is proposed, to make the diagnostic path faster, better, and more accurate.

Radiology of Dental Caries

Dental caries is a dynamic, preventable, reversible, complex biofilm-mediated, multifactorial disease that involves a series of demineralization/neutrality/remineralization of dental hard tissue in primary and permanent dentition. An imbalance in the continuum with a net demineralization over time results in the initiation of caries lesions. Visual inspection and intraoral radiographs are vital in caries detection, although they are of suboptimal sensitivity for early caries lesions. Shifting toward a conservative, noninvasive approach to caries management has resulted in the development of innovative-sensitive technologies. These newer techniques may serve as adjunct for the dental practitioner in detecting earliest changes in tooth structure.

Detection and analyzing plane of non-cavitated approximal caries by cross-polarized optical coherence tomography (CP-OCT)

OBJECTIVE

The objective was to assess the detection ability and the effect of analyzing plane of CP-OCT for non-cavitated approximal caries.

METHODS

Thirty human extracted premolars were selected based on micro-computed tomography [μ-CT: μ- CT = 0: sound (n = 12), μ-CT = 1/2: caries into outer-/inner-half of enamel (n = 6 each), μ-CT = 3: caries into outer one-third of dentine (n = 6)]. Teeth were mounted in a custommade device to simulate approximal contact, and scanned from the marginal ridge above the contact area. CP-OCT images were analyzed by deepest caries extension from horizontal and coronal planes, and repeated 48-hrs later. Sensitivity, specificity,percent correct, area under the ROC curve (Az), intra-examiner repeatability and correlation with μ-CT were determined.

RESULTS

Sensitivity/specificity/Az for Horizontalplane, Coronal-plane, and Deepest from both planes were 94percent/58percent/0.76,81percent/100percent/0.90, and 94 %/58 %/0.82. Coronal-plane had significantly higher specificity than Horizontal-plane and Deepest (p = 0.004) but Horizontal-plane and Deepest were not different (p = 1.00). Horizontal-plane had significantly lower Az than Deepest (p = 0.048), but Coronal-plane was not different than Horizontal-plane (p = 0.07) or Deepest (p = 0.20). Correlation coefficients were Horizontal-plane (0.53, p < 0.001), Coronal-plane (0.84, p < 0.001), and Deepest (0.66, p < 0.001).

CONCLUSION

Within the limitations of this study, CP-OCT could be used to detect non-cavitated approximal caries. Analysis using the Coronal-plane is superior to the Horizontal-plane.

CLINICAL SIGNIFICANCE

It is challenging to detect non-cavitated approximal caries clinically due to the adjacent tooth. CP-OCT is a nondestructive, no ionized-radiation caries detection technique. CP-OCT seems suitable to detect non-cavitated approximal caries and observing the Coronal-plane appears better than Horizontal-plane.

Dental Diagnosis and Treatment Assessments: Between X-rays Radiography and Optical Coherence Tomography

A correct diagnosis in dental medicine is typically provided only after clinical and radiological evaluations. They are also required for treatment assessments. The aim of this study is to establish the boundaries from which a modern, although established, imaging technique, Optical Coherence Tomography (OCT), is more suitable than the common X-ray radiography to assess dental issues and treatments. The most common methods for daily-basis clinical imaging are utilized in this study for extracted teeth (but also for other dental samples and materials), i.e., panoramic, intraoral radiography, and three-dimensional (3D) cone beam computed tomography (CBCT). The advantages of using OCT as an imaging method in dentistry are discussed, with a focus on its superior image resolution. Drawbacks related to its limited penetration depth and Field-of-View (FOV) are pointed out. High-quality radiological investigations are performed, measurements are done, and data collected. The same teeth and samples are also imaged (mostly) with an in-house developed Swept Source (SS)-OCT system, Master-Slave enhanced. Some of the OCT investigations employed two other in-house developed OCT systems, Spectral Domain (SD) and Time Domain (TD). Dedicated toolbars from Romexis software (Planmeca, Helsinki, Finland) are used to perform measurements using both radiography and OCT. Clinical conclusions are drawn from the investigations. Upsides and downsides of the two medical imaging techniques are concluded for each type of considered diagnosis. For treatment assessments, it is concluded that OCT is more appropriate than radiography in all applications, except bone-related investigations and periodontitis that demand data from higher-penetration depths than possible with the current level of OCT technology.

Semi-automated registration and segmentation for gingival tissue volume measurement on 3D OCT images

The change in gingival tissue volume may be used to indicate changes in gingival inflammation, which may be useful for the clinical assessment of gingival health. Properly quantifying gingival tissue volume requires a robust technique for accurate registration and segmentation of longitudinally captured 3-dimensional (3D) images. In this paper, a semi-automated registration and segmentation method for micrometer resolution measurement of gingival-tissue volume is proposed for 3D optical coherence tomography (OCT) imaging. For quantification, relative changes in gingiva tissue volume are measured based on changes in the gingiva surface height using the tooth surface as a reference. This report conducted repeatability tests on this method drawn from repeated scans in one patient, indicating an error of the point cloud registration method for oral OCT imaging is 63.08 ± 4.52µm (1σ), and the measurement error of the gingival tissue average thickness is -3.40 ± 21.85µm (1σ).

Measurement of Oral Epithelial Thickness by Optical Coherence Tomography

Optical coherence tomography (OCT) is a real-time, in-situ, non-invasive imaging device that is able to perform a cross-sectional evaluation of tissue microstructure based on the specific intensity of back-scattered and reflected light. The aim of the present study was to define normal values of epithelial thickness within the oral cavity. OCT measurements of epithelial thickness were performed in 28 healthy patients at six different locations within the oral cavity. Image analysis was performed using Image J 1.52 software. The healthy epithelium has a mean thickness of 335.59 ± 150.73 µm. According to its location within the oral cavity, the epithelium showed highest values in the region of the buccal mucosa (659.79 µm) and the thinnest one was observed in the mouth’s floor (100.07 µm). OCT has been shown to be useful for the evaluation of oral mucosa in vivo and in real time. Our study provides reference values for the epithelial thickness of multiple sites within the oral cavity. Knowledge of the thickness values of healthy mucosa is, therefore, of fundamental importance.

Diagnostic accuracy of optical coherence tomography for bladder cancer: A systematic review and meta-analysis

BACKGROUND

Bladder cancer is the fourth most common malignancy in men and a considerable disease burden globally. Multiple studies have focused on the accuracy of optical coherence tomography for bladder cancer diagnosis; however, the findings are inconsistent. Here, we assessed the accuracy of optical coherence tomography for bladder cancer diagnosis.

METHODS

Embase, PubMed, Medline, Web of Science, and the Cochrane Library database were searched for relevant studies from the earliest date available through March 11, 2019. Studies evaluating the accuracy of optical coherence tomography bladder cancer diagnosis were included. Pooled sensitivity, specificity, and area under the curve values of weighted symmetric summary receiver operating curves, were calculated at the per-lesion level.

RESULTS

Eleven studies, with a total of 1933 lesions, were included in the final analysis. The pooled results indicated that optical coherence tomography can differentiate bladder cancer from benign lesions: sensitivity, 94.9% (95% confidence interval: 92.7%-96.6%); specificity, 84.6% (95% confidence interval: 82.6%-86.4%); area under the curve, 0.97. Moreover, compared with optical coherence tomography alone, combined optical coherence tomography and fluorescence cystoscopy increased the diagnostic accuracy (sensitivity, 94.3% vs. 87.3%; specificity, 89.2% vs. 73.9%). Cross-polarization optical coherence tomography could also distinguish bladder cancer from normal tissue: sensitivity, 92.0% (95% confidence interval: 87.0%-95.6%); specificity, 84.4% (95% confidence interval: 81.7%-86.9%); area under the curve, 0.95.

CONCLUSIONS

Optical coherence tomography can accurately differentiate malignant from benign bladder lesions, particularly when combined with fluorescence cystoscopy.

Quantitative assessment of rat bone regeneration using complex master-slave optical coherence tomography

BACKGROUND

The need for hard and soft tissues in oral implantology determined the development of methods and techniques to increase bone volume and their quality with different alternative materials used as substituents of patient's natural bone. In addition, laser radiation can be used to accelerate the repair of fractures and to produce an increased volume of formed callus, as well as an increased bone mineral density.

METHODS

The aim of this work is to evaluate the capability of an in-house developed multimodal complex master slave (CMS) enhanced swept source (SS) optical coherence tomography (OCT) imaging instrument to analyze the increase in the quantity and the improvement of the quality of newly-formed bone using low level laser therapy (LLLT). Bone formation is quantitatively assessed in 5 mm cylindrical defects made in the calvaria part of the skull of living rats. Samples are divided in three study groups: A, a negative control group, for which the natural healing process of the defect is investigated; B, a positive control group, for which bovine graft is used to stimulate bone formation, and C, a study group, in which bovine graft is added to the created defects and LLLT is applied throughout the entire healing period. The animals are sacrificed after 14, 21, and 30 days, and the samples are imaged using the multimodal CMS/SS-OCT instrument.

RESULTS

The method allows for the simultaneous monitoring of the bone tissue via two perpendicular cross-sections and nine en-face images taken at adjustable depths into the sample. A global image with course axial resolution allows for the positioning of the field-of-view of the system on the area of interest on the tissue. The quantitative assessment of the process of bone formation is completed using the differences in brightness between the native bone, the artificial bone graft, and the newly-formed bone.

CONCLUSIONS

Group C is demonstrated to have a higher volume of newly-formed bone than Group B, which is better from this point of view than Group A. By analyzing the evolution of this volume of new bone in time, the most significant difference was after 21 days, therefore approximately after two thirds of the total time interval analyzed. After 30 days, the volumes of bone tend to move closer, as they begin to fill the available gap. The study demonstrates that OCT can assess quantitatively the positive impact of LLLT on bone regeneration.

Optical coherence tomography imaging of cardiac substrates

Cardiovascular disease is the leading cause of morbidity and mortality in the United States. Knowledge of a patient's heart structure will help to plan procedures, potentially identifying arrhythmia substrates, critical structures to avoid, detect transplant rejection, and reduce ambiguity when interpreting electrograms and functional measurements. Similarly, basic research of numerous cardiac diseases would greatly benefit from structural imaging at cellular scale. For both applications imaging on the scale of a myocyte is needed, which is approximately 100 µm × 10 µm. The use of optical coherence tomography (OCT) as a tool for characterizing cardiac tissue structure and function has been growing in the past two decades. We briefly review OCT principles and highlight important considerations when imaging cardiac muscle. In particular, image penetration, tissue birefringence, and light absorption by blood during in vivo imaging are important factors when imaging the heart with OCT. Within the article, we highlight applications of cardiac OCT imaging including imaging heart tissue structure in small animal models, quantification of myofiber organization, monitoring of radiofrequency ablation (RFA) lesion formation, structure-function analysis enabled by functional extensions of OCT and multimodal analysis and characterizing important substrates within the human heart. The review concludes with a summary and future outlook of OCT imaging the heart, which is promising with progress in optical catheter development, functional extensions of OCT, and real time image processing to enable dynamic imaging and real time tracking during therapeutic procedures.

Optical Coherence Tomography Investigations and Modeling of the Sintering of Ceramic Crowns

Dental prostheses are sintered in ovens that sometimes suffer from a loss of calibration. This can lead to variations of the sintering temperature outside the range recommended by the manufacturer. Stress and even fractures in dental ceramics may occur, and this leads to the necessity to rebuild the dental construct. The aim of this work is to monitor the quality of sintering processes using an established biomedical imaging technique-optical coherence tomography (OCT). Conventional current procedures imply the fabrication of supplemental samples that add to the expenses and are only evaluated visually. To our knowledge, we were the first to propose the use of OCT, a non-destructive method that brings objectivity for such assessments, focusing, in a previous study, on metal ceramic dental prostheses. Here, a different material, pressed ceramics, is considered, while we propose a quantitative assessment of the results-using reflectivity profiles of en-face (i.e., constant-depth) OCT images of sintered samples. The results for both the pressed ceramics and metal ceramics prostheses are discussed by obtaining the analytic functions of their reflectivity profiles. A multi-parametric analysis demonstrates the best parameter to characterize the loss of calibration of dental ovens. Rules-of-thumb are extracted; producing dental prostheses with defects can thus be avoided.

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.

A noninvasive imaging and measurement using optical coherence tomography angiography for the assessment of gingiva: An in vivo study

Gingiva is the soft tissue that surrounds and protects the teeth. Healthy gingiva provides an effective barrier to periodontal insults to deeper tissue, thus is an important indicator to a patient's periodontal health. Current methods in assessing gingival tissue health, including visual observation and physical examination with probing on the gingiva, are qualitative and subjective. They may become cumbersome when more complex cases are involved, such as variations in gingival biotypes where feature and thickness of the gingiva are considered. A noninvasive imaging technique providing depth-resolved structural and vascular information is necessary for an improved assessment of gingival tissue and more accurate diagnosis of periodontal status. We propose a three-dimensional (3D) imaging technique, optical coherence tomography (OCT), to perform in situ imaging on human gingiva. Ten volunteers (five male, five female, age 25-35) were recruited; and the labial gingival tissues of upper incisors were scanned using the combined use of state-of-the-art swept-source OCT and OCT angiography (OCTA). Information was collected describing the 3D tissue microstructure and capillary vasculature of the gingiva within a penetration depth of up to 2 mm. Results indicate significant structural and vascular differences between the two extreme gingival biotypes (ie, thick and thin gingiva), and demonstrate special features of vascular arrangement and characteristics in gingival inflammation. Within the limit of this study, the OCT/OCTA technique is feasible in quantifying different attributes of gingival biotypes and the severity of gingival inflammation.

Optical coherence tomography in Optics Express [Invited]

Optical coherence tomography (OCT) is one of the most successful technologies in the history of biomedical optics. Optics Express played an important role in communicating groundbreaking technological achievements in the field of OCT, and, conversely, OCT papers are among the most frequently cited papers published in Optics Express. On the occasion of the 20th anniversary of the journal, this review analyzes the reasons for the success of OCT papers in Optics Express and discusses possible motivations for researchers to submit some of their best OCT papers to the journal.

Application of optical and spectroscopic technologies for the characterization of carious lesions in vitro

The detection of the beginning demineralization process of dental hard tissue remains a challenging task in dentistry. As an alternative to bitewing radiographs, optical and spectroscopic technologies showed promising results for caries diagnosis. The aim of the present work is to give an overview of optical and spectroscopic properties of healthy and carious human teeth in vitro by means of Raman spectroscopy (RS), optical coherence tomography (OCT) and hyperspectral imaging (HSI). OCT was able to represent microstructural changes below the enamel surface and revealed increased scattering for white spot lesions and a white scattering trail for deeper lesions. HSI showed similar absorbance characteristics for healthy and demineralized enamel over the entire spectrum and a characteristic absorbance peak at 550 nm for discolored lesions. Already at early carious stages (white spot), we found a distinct loss of hydroxylapatite-related intensity at 959 cm−1 in demineralized regions with RS. Healthy and demineralized tooth surfaces can be distinguished at different signal levels by means of RS, OCT and HSI. The presented modalities provide additional information to the current clinical diagnosis of caries such as microstructural changes, quantification of the demineralization and imaging of caries-related chemical changes.

In vitro and clinical evaluation of optical coherence tomography for the detection of subgingival calculus and root cementum

This study evaluated the effectiveness of swept-source optical coherence tomography (ss-OCT) for detecting calculus and root cementum during periodontal therapy. Optical coherence tomography (OCT) images were taken before and after removal of subgingival calculus from extracted teeth and compared with non-decalcified histological sections. Porcine gingival sheets of various thicknesses were applied to the root surfaces of extracted teeth with calculus and OCT images were taken. OCT images were also taken before and after scaling and root planing (SRP) in human patients. In vitro, calculus was clearly detected as a white-gray amorphous structure on the root surface, which disappeared after removal. Cementum was identified as a thin, dark-gray layer. The calculus could not be clearly observed when soft tissues were present on the root surface. Clinically, supragingival calculus and cementum could be detected clearly with OCT, and subgingival calculus in the buccal cervical area of the anterior and premolar teeth was identified, which disappeared after SRP. Digital processing of the original OCT images was useful for clarifying the calculus. In conclusion, ss-OCT showed potential as a periodontal diagnostic tool for detecting cementum and subgingival calculus, although the practical applications of subgingival imaging remain limited.

Optical coherence tomography to evaluate variance in the extent of carious lesions in depth

Evaluation of variance in the extent of carious lesions in depth at smooth surfaces within the same ICDAS code group using optical coherence tomography (OCT) in vitro and in vivo. (1) Verification/validation of OCT to assess non-cavitated caries: 13 human molars with ICDAS code 2 at smooth surfaces were imaged using OCT and light microscopy. Regions of interest (ROI) were categorized according to the depth of carious lesions. Agreement between histology and OCT was determined by unweighted Cohen's Kappa and Wilcoxon test. (2) Assessment of 133 smooth surfaces using ICDAS and OCT in vitro, 49 surfaces in vivo. ROI were categorized according to the caries extent (ICDAS: codes 0-4, OCT: scoring based on lesion depth). A frequency distribution of the OCT scores for each ICDAS code was determined. (1) Histology and OCT agreed moderately (κ = 0.54, p ≤ 0.001) with no significant difference between both methods (p = 0.25). The lesions (76.9% (10 of 13)) _were equally scored. (2) In vitro, OCT revealed caries in 42% of ROI clinically assessed as sound. OCT detected dentin-caries in 40% of ROIs visually assessed as enamel-caries. In vivo, large differences between ICDAS and OCT were observed. Carious lesions of ICDAS codes 1 and 2 vary largely in their extent in depth.

Multicontrast endomyocardial imaging by single-channel high-resolution cross-polarization optical coherence tomography

A single-channel high-resolution cross-polarization (CP) optical coherence tomography (OCT) system is presented for multicontrast imaging of human myocardium in one-shot measurement. The intensity and functional contrasts, including the ratio between the cross- and co-polarization channels as well as the cumulative retardation, are reconstructed from the CP-OCT readout. By comparing the CP-OCT results with histological analysis, it is shown that the system can successfully delineate microstructures in the myocardium and differentiate the fibrotic myocardium from normal or ablated myocardium based on the functional contrasts provided by the CP-OCT system. The feasibility of using A-line profiles from the 2 orthogonal polarization channels to identify fibrotic myocardium, normal myocardium and ablated lesion is also discussed.

Observation and determination of periodontal tissue profile using optical coherence tomography

BACKGROUND AND OBJECTIVE

Diagnosis is a crucial step in periodontal treatment. The aim of this study was to evaluate the effectiveness of optical coherence tomography (OCT) for observation and determination of periodontal tissue profiles in vivo.

MATERIAL AND METHODS

In experiment 1, refractive indices of purified water, porcine gingiva and human gingiva at 1330 nm were determined for the analysis of OCT images of periodontal tissues. In experiment 2, OCT examination was performed in the midlabial apico-coronal plane of mandibular anteriors in 30 Asian volunteers with healthy gingiva. Sulcus depth was measured on intra-oral photographs taken during probing. In the OCT images, the gingival, epithelial and connective tissue thickness, and the position of alveolar bone crest were determined and finally, the biologic width was measured.

RESULTS

Refractive indices of purified water, porcine gingiva and human gingiva were 1.335, 1.393 and 1.397, respectively. Cross-sectional images of gingival epithelium, connective tissue and alveolar bone were depicted in real-time. The sulcular and junctional epithelium could be visualized occasionally. Laser penetration and reflection were limited to a certain depth with an approximate maximal imaging depth capability of 1.5 mm and OCT images of the periodontal structure were not clear in some cases. The average maximal thickness of gingiva and epithelium and biologic width at the mandibular anteriors were 1.06 ± 0.21, 0.49 ± 0.15 and 2.09 ± 0.60 mm, respectively.

CONCLUSION

OCT has promise for non-invasive observation of the periodontal tissue profile in detail and measurement of internal periodontal structures including biologic width in the anterior region.

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.

The potential role of in vivo optical coherence tomography for evaluating oral soft tissue: A systematic review

BACKGROUND

The introduction of optical coherence tomography (OCT) in dentistry enabled the integration of already existing clinical and laboratory investigations in the study of the oral cavity. This systematic review presents an overview of the literature, to evaluate the usefulness of in vivo OCT for diagnosing oral soft tissues lesions, to compare the OCT results with traditional histology, and to identify limitations in prior studies so as to improve OCT applications.

METHODS

We performed a review of the literature using different search engines (PubMed, ISI Web of Science, and the Cochrane Library) employing MeSH terms such as "optical coherence tomography" and "OCT" in conjunction with other terms. We utilized the Population, Intervention, Comparison, Outcomes, and Study design (PICOS) method to define our study eligibility criteria.

RESULTS

Initial results were 3155. In conclusion, there were only 27 studies which met our selection criteria. We decided to allocate the 27 selected items into three groups: healthy mucosa; benign, premalignant, and malignant lesions; and oral manifestations of systemic therapies or pathological conditions.

CONCLUSIONS

Although the OCT is an easy-to-perform test and it offers an attractive diagnostic and monitoring prospect for soft tissues of the oral cavity, further studies are needed to complete the current knowledge of this imaging technique.

OCT assessment of non-cavitated occlusal carious lesions by variation of incidence angle of probe light and refractive index matching

OBJECTIVES

This study evaluated (1) the detection and assessment of non-cavitated occlusal carious lesions by spectral domain optical coherence tomography (SD-OCT) and (2) the impact of varying angle of incidence (AI) of probe light and refractive index matching (RIM).

METHODS

Nine extracted human molars with 18 occlusal lesions (ICDAS code 2) were visually selected. 18 regions of interest (ROI) were imaged with SD-OCT under varying AI (0°, ±5°, ±10°, ±15°) and with/without application of glycerine at 0°. X-ray micro computed tomography (μCT) was used as a validation standard. μCT and OCT signals were categorized according to the lesion extent: 1-sound, 2-lesion limited to half of enamel, 3-lesion limited to enamel, 4-lesion into dentin. Agreement between both methods was assessed. Intra- and inter-examiner reproducibility analyses were conducted.

STATISTICS

Cohen's kappa coefficient (κ), Spearman's rho correlation (r_s) and Wilcoxon test (α=0.05).

RESULTS

Slight to moderate agreement (κ=0.153) between μCT and OCT was obtained at an AI of 0° (Wilcoxon: p=0.02). With variation of Al a substantial agreement (κ=0.607) was observed (p=0.74). Spearman's correlation between both methods was 0.428 at 0°, 0.75 with varying AI and 0.573 with glycerine. Kappa values for intra-and inter-examiner analysis ranged between 0.81 and 0.88 and between 0.25 and 0.73, respectively.

CONCLUSION

Variation of AI improves the detectability of non-cavitated occlusal carious lesions. RIM can enhance signal-to-noise ratio.

CLINICAL RELEVANCE

OCT could provide additional diagnostic information in single and longitudinal assessments of occlusal carious lesions.

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.

Improved accuracy in periodontal pocket depth measurement using optical coherence tomography

Purpose

The purpose of this study was to examine whether periodontal pocket could be satisfactorily visualized by optical coherence tomography (OCT) and to suggest quantitative methods for measuring periodontal pocket depth.

Methods

We acquired OCT images of periodontal pockets in a porcine model and determined the actual axial resolution for measuring the exact periodontal pocket depth using a calibration method. Quantitative measurements of periodontal pockets were performed by real axial resolution and compared with the results from manual periodontal probing.

Results

The average periodontal pocket depth measured by OCT was 3.10±0.15 mm, 4.11±0.17 mm, 5.09±0.17 mm, and 6.05±0.21 mm for each periodontal pocket model, respectively. These values were similar to those obtained by manual periodontal probing.

Conclusions

OCT was able to visualize periodontal pockets and show attachment loss. By calculating the calibration factor to determine the accurate axial resolution, quantitative standards for measuring periodontal pocket depth can be established regardless of the position of periodontal pocket in the OCT image.

Comparisons of the diagnostic accuracies of optical coherence tomography, micro-computed tomography, and histology in periodontal disease: an ex vivo study

Purpose

Optical coherence tomography (OCT) is a noninvasive diagnostic technique that may be useful for both qualitative and quantitative analyses of the periodontium. Micro-computed tomography (micro-CT) is another noninvasive imaging technique capable of providing submicron spatial resolution. The purpose of this study was to present periodontal images obtained using ex vivo dental OCT and to compare OCT images with micro-CT images and histologic sections.

Methods

Images of ex vivo canine periodontal structures were obtained using OCT. Biologic depth measurements made using OCT were compared to measurements made on histologic sections prepared from the same sites. Visual comparisons were made among OCT, micro-CT, and histologic sections to evaluate whether anatomical details were accurately revealed by OCT.

Results

The periodontal tissue contour, gingival sulcus, and the presence of supragingival and subgingival calculus could be visualized using OCT. OCT was able to depict the surface topography of the dentogingival complex with higher resolution than micro-CT, but the imaging depth was typically limited to 1.2–1.5 mm. Biologic depth measurements made using OCT were a mean of 0.51 mm shallower than the histologic measurements.

Conclusions

Dental OCT as used in this study was able to generate high-resolution, cross-sectional images of the superficial portions of periodontal structures. Improvements in imaging depth and the development of an intraoral sensor are likely to make OCT a useful technique for periodontal applications.

Enamel Quality after Debonding: Evaluation by Optical Coherence Tomography

The aims of this study were to evaluate quantitatively the enamel fractures, adhesive remnants and bracket fragments on enamel after debonding of metal and ceramic brackets, and to quantify the layer of adhesive remnants in depth after two different cleanup procedures. Metal and ceramic brackets were bonded on 120 human incisors and then debonded using two different techniques with Side Cutter (SC) and Anterior Bracket Removal plier (ABR). After this, a high-speed tungsten carbide finishing bur or a low-speed tungsten carbide finishing bur was used. The debonded samples were submitted to enamel assessment with optical coherence tomography (OCT). In sequence, two different methods of removing the remaining adhesive (tungsten carbide burs at high and low speed) were performed and at the end of these procedures, the remaining adhesive layer was measured with OCT. The results demonstrated that enamel fractures were observed only in the samples bonded with ceramic brackets, and the type of pliers did not influence the incidence and extent of enamel damage. Moreover, the type of debonding technique (with side-cutting pliers or anterior bracket removal pliers) and the type of bracket did not influence the amount of adhesive remaining after debonding. The burs at low speed removed the remaining adhesive more effectively during cleanup procedures.

Optical changes of dentin in the near-IR as a function of mineral content

The optical properties of human dentin can change markedly due to aging, friction from opposing teeth, and acute trauma, resulting in the formation of transparent or sclerotic dentin with increased mineral density. The objective of this study was to determine the optical attenuation coefficient of human dentin tissues with different mineral densities in the near-infrared (NIR) spectral regions from 1300-2200 nm using NIR transillumination and optical coherence tomography (OCT). N=50 dentin samples of varying opacities were obtained by sectioning whole extracted teeth into ~ 150 μm transverse sections at the cemento-enamel junction or the apical root. Transillumination images were acquired with a NIR camera and attenuation measurements were acquired at various NIR wavelengths using a NIR sensitive photodiode. Samples were imaged with transverse microradiography (gold standard) in order to determine the mineral density of each sample.

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.

Evaluation of the effects of fluoride-releasing varnish on dentin demineralization using optical coherence tomography

Effects of a fluoride-releasing varnish containing surface reaction-type prereacted glass ionomer (S-PRG) filler on dentin demineralization were examined using optical coherence tomography. Bovine incisors that were sliced and treated with undersaturated 0.1 M lactic acid buffer solution (DE group). A thin film of varnish-containing S-PRG filler was applied before demineralization (PRG group). Control was maintained in artificial saliva. Using optical coherence tomography of selected locations on the dentin surface, peak intensity (dB) and width (μm) at 1/e(2) were obtained and integrated values calculated. Although alterations in integrated values were different in each group, there was a slight but not significant increase in those for the control group and a slight but significant increase for the De group. For the PRG group, integrated values were doubled seven days after experiment initiation, followed by a significant increase. Fluoride-releasing varnish containing S-PRG fillers prevented dentin demineralization as detected by optical coherence tomography.

Dark field optical imaging reveals vascular changes in an inducible hamster cheek pouch model during carcinogenesis

In this study, we propose a low-cost cross-polarized dark field microscopy system for in vivo vascular imaging to detect head and neck cancer. A simple-to-use Gabor-filter-based image processing technique was developed to objectively and automatically quantify several important vascular features, including tortuosity, length, diameter and area fraction, from vascular images. Simulations were performed to evaluate the accuracies of vessel segmentation and feature extraction for our algorithm. Sensitivity and specificity for vessel segmentation of the Gabor masks both remained above 80% at all contrast levels when compared to gold-standard masks. Errors for vascular feature extraction were under 5%. Moreover, vascular contrast and vessel diameter were identified to be the two primary factors which affected the segmentation accuracies. After our algorithm was validated, we monitored the blood vessels in an inducible hamster cheek pouch carcinogen model over 17 weeks and quantified vascular features during carcinogenesis. A significant increase in vascular tortuosity and a significant decrease in vessel length were observed during carcinogenesis.

Comparison of the marginal adaptation of direct and indirect composite inlay restorations with optical coherence tomography

Objective

The purpose of the study was to use the photonic imaging modality of optical coherence tomography (OCT) to compare the marginal adaptation of composite inlays fabricated by direct and indirect techniques.

Material and Methods

Class II cavities were prepared on 34 extracted human molar teeth. The cavities were randomly divided into two groups according to the inlay fabrication technique. The first group was directly restored on cavities with a composite (Esthet X HD, Dentsply, Germany) after isolating. The second group was indirectly restored with the same composite material. Marginal adaptations were scanned before cementation with an invisible infrared light beam of OCT (Thorlabs), allowing measurement in 200 µm intervals. Restorations were cemented with a self-adhesive cement resin (SmartCem2, Dentsply), and then marginal adaptations were again measured with OCT. Mean values were statistically compared by using independent-samples t-test and paired samples t-test (p<0.05), before and after cementation.

Results

Direct inlays presented statistically smaller marginal discrepancy values than indirect inlays, before (p=0.00001442) and after (p=0.00001466) cementation. Marginal discrepancy values were increased for all restorations after cementation (p=0.00008839, p=0.000000952 for direct and indirect inlays, respectively). The mean marginal discrepancy value of the direct group increased from 56.88±20.04 µm to 91.88±31.7 µm, whereas the indirect group increased from 107.54±35.63 µm to 170.29±54.83 µm. Different techniques are available to detect marginal adaptation of restorations, but the OCT system can give quantitative information about resin cement thickness and its interaction between tooth and restoration in a nondestructive manner.

Conclusions

Direct inlays presented smaller marginal discrepancy than indirect inlays. The marginal discrepancy values were increased for all restorations that refer to cement thickness after cementation.

Development of a hybrid Raman spectroscopy and optical coherence tomography technique for real-time in vivo tissue measurements

We report on the development of a unique sideview handheld hybrid Raman spectroscopy (RS) and optical coherence tomography (OCT) technique for real-time in vivo tissue measurements. A sideview handheld RS-OCT optical probe is designed to coalign the optical paths of RS and OCT sampling arms, whereby a compact long-pass dichroic mirror (LPDM) is utilized to transmit the OCT signal through a gradient index rod lens and a reflection mirror, whereas the LPDM deflects the tissue Raman signal by 90°, leading to coaligned RS/OCT optical samplings on the tissue. Further study shows that the hybrid RS and OCT technique developed is capable of simultaneously acquiring both morphological and biochemical information about the oral tissue in vivo, facilitating real-time, in vivo tissue diagnoses and characterizations in the oral cavity.

Ultrastructural features of dentinoenamel junction revealed by focused gallium ion beam milling

To take full advantage of focused ion beam (FIB) in preparation of ultrathin sections of biological tissues, we have used a cryo-milling process. In this study, extracted human teeth were scanned by optical coherence tomography to inspect the samples for intactness and to determine the area of interest. Then, the selected area of interest was cross-sectioned for examination under a confocal laser scanning microscope to determine the target location of the dentinoenamel junction (DEJ) that was later milled by cryo-FIB at preset parameters, followed by transmission electron microscope examination of the final sliced specimens for ultrastructural characterization. The proposed technique was able to outline the DEJ and to identify the different tooth layers in a single section, without artefacts or tissue damage. The DEJ was outlined as fine longitudinal projections intermingling between the solid electron-dense enamel and intricate electron-lucent hollow dentin. In conclusion, this study has shown the great potential of cryo-FIB in handling different biological tissues having different physical properties, with great precision and accuracy and minimum artefacts.

Importance sampling-based Monte Carlo simulation of time-domain optical coherence tomography with embedded objects

Monte Carlo simulation for light propagation in biological tissue is widely used to study light-tissue interaction. Simulation for optical coherence tomography (OCT) studies requires handling of embedded objects of various shapes. In this work, time-domain OCT simulations for multilayered tissue with embedded objects (such as sphere, cylinder, ellipsoid, and cuboid) was done. Improved importance sampling (IS) was implemented for the proposed OCT simulation for faster speed. At first, IS was validated against standard and angular biased Monte Carlo methods for OCT. Both class I and class II photons were in agreement in all the three methods. However, the IS method had more than tenfold improvement in terms of simulation time. Next, B-scan images were obtained for four types of embedded objects. All the four shapes are clearly visible from the B-scan OCT images. With the improved IS B-scan OCT images of embedded objects can be obtained with reasonable simulation time using a standard desktop computer. User-friendly, C-based, Monte Carlo simulation for tissue layers with embedded objects for OCT (MCEO-OCT) will be very useful for time-domain OCT simulations in many biological applications.