This PDF file contains the front matter associated with SPIE Proceedings Volume 10857, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Dental caries is one of the most important oral global health burdens. Even though the scientific community has a good understanding of its etiology, almost 100% of the population still present dental caries in one form or another. Different reasons such as lack of oral health education, symptom-driven consultations and late caries detection may be considered as the main explanations. Recently, new noninvasive therapies showed an important protective effect against caries progression. These new treatment options can be mainly applied in case of non cavitated lesions, thus the need for early caries detection becomes crucial. With novel near infrared technologies, early enamel lesions can be detected and monitored over time to provide information on the lesions’ activity and the caries risk level. The long-term monitoring of early lesions- treated or not - is now possible with near infrared caries detection tools. With no ionizing radiation required, frequent imaging of the lesions is possible for high risk patients. Near infrared early caries detection can improve the success rate of noninvasive preventive and therapeutic measures, while providing the opportunity to monitor carious lesions in their early stages and to offer a large window of opportunity for early intervention, when necessary.

The detection of incipient carious lesions is crucial for the preservation of dental hard tissue with preventive therapies. Optical coherence tomography (OCT) based imaging has been proofed to be a valuable methodology for the depth-resolved detection of alterations at dental hard tissue. Due to changes of birefringent properties at carious lesions, the measurement of polarization properties with polarization-sensitive OCT (PS-OCT) provides an additional contrast that could enhance the detection of incipient carious lesions. The aim of the present study was to monitor changes of polarization properties during the initial demineralization process by means of PS-OCT. Therefore, 18 bovine enamel palates were demineralized up to 7 weeks in an artificial demineralization model using lactate acid and buffer solution to mimic natural caries progression. The palates were stored at pH 5.5 and 35°C with constant fluid movement. In order to detect changes of depolarization at different stages of demineralization, the degree of polarization uniformity (DOPU) was calculated from PS-OCT measurements, performed under wet and dry conditions. In addition, polarization microscopy and micro-computed tomography of thin sections were analyzed to assess lesion depth and mineral loss. Our main finding is that consecutive stages of demineralization are correlated to an increasing DOPU contrast between sound enamel and the lesion area, where the lesion area is connected to decreasing DOPU values. Our results show that PS-OCT based imaging of birefringence changes is sensitive to very early stages of the demineralization process and adds a valuable contrast for the detection and monitoring of incipient enamel lesions.

3D scans of dental arches and the 3D print technique in orthodontics have become every important part of clinical practice. The aim of our study was 3D objectification of stereolithography system (SLA) printed models in comparison with Fused Deposition Modeling (FDM), Polyjet (PJ) technology, and Selective Laser Sintering (SLS). The 50 scans of upper dental arches of medical students were prepared using 3Shape TRIOS 3. After then SLA 3D Printer Formlabs 2 built step by step layers of an upper dental arch model using liquid polymer hardened by laser beam (blue 405 nm laser). The study compared precision of 3D SLA, PDM, PJ and SLS models along all 3 axes.

In dentistry, 3D IOS (intra-oral scanners) are gaining an increasing popularity essentially for the production of dental prostheses. Until now, there is no normalized procedure to determine the resolution of IOS. Such a procedure could be a positive parameter for the IOS market and a first step in their normalization. The aim of this study is to present a reproducible methodology to estimate the noise and resolution of any type of IOS. For the noise, we used the IOS Trios 2 (3Shape) and the Carestream 3500 (Carestream) for noise and resolution. As reference, we used an ultra-flat and ultra-smooth alumina. Being perfectly flat, any record of roughness should be interpreted as noise. In this study, the root mean square (RMS) values obtained are ranged between 5.29 and 12.58 micrometers. Significant differences have been found between the central part and the whole mesh. This is due to edge effect: deviation from a flat surface is more important on the edge of meshes than the internal part. To evaluate the resolution, a ceramic tip, well-polished was recorded with the IOS’s and compared to the mesh obtained with micro tomography (5 micrometer resolution). We measured the distance between the two plans of the tip, considered as the small detail recorded. We found a distance from 89 to 121 micrometers with IOS studied and 25 micrometers with micro CT. Those methods, simple and reproducible, could be perfectly suitable to evaluate and compare commercial all types of IOS’s.

For future non-invasive optical biopsy by OCT, there is a demand to relate the obtained scans with histological cross sections, which represent the diagnostic gold standard. For this reason, the aim of the performed study was the qualitative matching of OCT cross-sectional images with histological pictures from various image databases. Therefore, the human oral mucosa of forty-seven healthy volunteers was investigated at ten different regions, e.g. lip, floor of mouth, hard and soft palate, by using the recently proposed in vivo endoscopic rigid handheld OCT system (central wavelength: λ = 840 nm, spatial resolution: 11.6 μm axial and 17.4 μm lateral). The results allow answering the question, whether OCT imaging is able to detect sublayers of mucosa and to clearly identify tissue structures by using a qualitative scoring system. In fact, depiction of epithelium, lamina propria and configurations like blood vessels and salivary glands, respectively, is possible, whereas a sufficient visualization of deep submucosa or epithelial sublayers cannot be achieved with the used wavelength range. Despite a well-defined surface profile, evaluating the level of keratinization is challenging. In contrast to histological cross sections impaired by fixation, orientation and organisation of collagen fiber bundles are highlighted better in OCT cross sections due to the in vivo situation. With regard to future clinical studies, correct interpretation of tissue structure in healthy individuals forms the basis to identify and assess pathomorphological changes related to various kinds of oral diseases by means of OCT.

We have developed a new tool to measure the acid production by plaque oral bacteria. Many species of oral bacteria metabolize sugars in food and produce organic acids that demineralize the dental enamel leading to the formation of cavities. Measuring the acidity level before and after a sugar rinse can indicate the susceptibility of an individual to tooth decay and location of active caries. In a case study on two subjects, a non-contact optics-based pH device was able to track pH before and after a sugar rinse. The fiber optic probe measures acidity level in difficult to access dental locations such as occlusal pits and fissures based on changes in the spectral fluorescence profile of fluorescein (FL) dye. Fiber coupled 420 nm LED excites 200uM aqueous FL solution in the mouth. The fluorescence spectrum in 450-650 nm range is obtained using an adjacent fiber optic cable coupled to a spectrometer. Chemometric analysis of endmember dianion and anion species using least-square fitting is performed to determine the pH of the FL absorbed into the extracellular region of the oral biofilm. Other unwanted noise, like background light and auto-fluorescence in the range of 450-650 nm is removed before calculating biofilm pH. Using this device in a darkened room on two subjects, we were able to measure resting pH (before a sugar rinse) and track time dependent change in pH (after a sugar rinse) in the range of pH 4-7 paving the way for first clinical optical pH measurement in the mouth.

Incipient enamel lesions represent an early phase of dental caries. They can be produced in-vitro by pH cycling. Raman spectral maps showed that the higher the organic/mineral ratio in the demineralized enamel, the lower is the intensity of mineral content in the same zone. Moreover, the evident red shift of the two-photon excited fluorescence (2PEF) spectrum from carious enamel, compared to that from sound enamel is typical of carious lesion formation. Second harmonic generation (SHG) signal was also observed in the lesion zone. The obtained results demonstrate a great potential for Raman, 2PEF and SHG photonic signals in diagnostic of incipient carious lesions.

Transparent remineralized surface zones found on natural caries lesions may reduce the permeability to water and plaque generated acids. Near-IR (NIR) reflectance imaging coupled with dehydration can be used to measure changes in the fluid permeability of lesions in enamel and dentin. Previous work demonstrated a negative association between the surface zone thickness and the rate of dehydration in simulated enamel lesions. In this study, the rates of dehydration and thickness of transparent surface layer of coronal lesions of extracted teeth were measured and correlated. Reflectance imaging at NIR wavelengths from 1695-1750 nm, which coincides with higher water absorption and manifests the greatest sensitivity to contrast changes during dehydration measurements, was used to image these enamel lesions. The remineralized surface layer thickness was determined using optical coherence tomography (OCT).

Near infrared imaging methods, including optical coherence tomography (OCT), have shown promise in assessing activity of enamel caries lesions. We present initial results in ex-vivo dental samples with a polarization diversity-detection OCT system complete with an integrated dental handpiece. Built around an Axsun Technologies swept source engine, images B-scans 12(x) by 7(z) mm at over 100 fps with 66um transverse and 7um depth resolution. Internal normal dental structure and lesions were imaged and compared with micro-CT. We demonstrate that the Axsun OCT prototype can detect the penetration of occlusal lesions to dentin and measure the penetration of approximal lesions when imaging from the occlusal surface.

This work aims was to correlate the changes in the optical attenuation coefficients obtained through the OCT technique with the values obtained in Knoop sectional microhardness tests over time in dental human enamel samples irradiated with the Nd: YAG laser and Acid Phosphate Fluoride (APF), aiming the prevention of caries lesions in vitro. After Ethical Committee approval, 160 enamel samples, obtained from 40 human tooth molars, were divided into 4 groups: Control group (where no treatment was performed); Fluoride group (APF - fluoride phosphate acidulated for 4 minutes); Fluoride-Laser group: APF followed by irradiation with Nd:YAG laser (DE = 84.9 J/cm2, contact mode, with the use of carbon paste as photoabsorver); Laser-fluoride group (irradiation with Nd:YAG laser followed by APF). The samples of all groups were subjected to pH cycling during 20 days. On days 5, 10, 15 and 20, 10 samples from each group were removed from the cycling for the Knoop sectional microhardness test. Two samples of each group, at each time, were randomly selected for the analysis with FTIR-ATR (Fourier transform infrared spectroscopy associated with attenuated total reflection technique). The analysis by ATR-FTIR showed changes in the chemical composition of the samples of the irradiated groups in relation to Control and Fluoride group. There was correlation between the values of sectional microhardness tests and the measured optical attenuation coefficient by OCT in irradiated dental enamel, showing that the association between fluoride application and Nd:YAG laser irradiation is an important tool for the prevention of tooth enamel demineralization.

In this study, we combined optical technology and machine learning to classify dental problems.We took totally 16 dental samples and 79 OCT images including 32 dental calculus(CA) images and 47 normal (HC) images. After image processing, we obtained optical attenuation coefficient, surface roughness and spectral information, and we put these features into two layer neural networks for training. We divided the data into training (24 CA / 37 HC = 61 total) and test (8 CA / 10 HC = 18 total) data, and the training data was checked with 10-fold cross validation to confirm no over-trained. The results showed that the model validity is 78%, and the test results have a sensitivity of 86%, specificity of 100%, and total accuracy of 94%.

The conventional approach for diagnosing dental caries is clinical examination and supplemented by radiographs. However, studies based on the clinical and radiographic examination methods often show low sensitivity and high specificity. Machine learning and deep learning techniques can be used to enhance optical coherence tomography (OCT) to more accurately identify diseased and damaged tissue. In this paper, we present a novel approach combining OCT imaging modality and deep convolutional neural network (CNN) for the detection of occlusal carious lesions. A total of 51 extracted human permanent teeth were collected and categorized into three groups: Non-carious teeth, caries extending into enamel, and caries extending into dentin. In data acquisition and ex-vivo OCT imaging, the samples were imaged using spectral-domain OCT system operating at 1300nm center wavelength with a scan rate of 5.5-76kHz, and axial resolution of 5.5μm in air. To acquire images with minimum inhomogeneity, imaging was performed multiple times at different points. For deep learning, OCT images of extracted human carious and non-carious teeth were input to a CNN classifier to determine variations in tissue densities resembling the demineralization process. The CNN model employs two convolutional and pooling layers to extract features and then classify each patch based on the probabilities from the SoftMax classification layer. The sensitivity and specificity of distinguishing between carious and non-carious lesions were found to be 98% and 100%, respectively. This proposed deep learning-based OCT method can reliably classify the oral tissues with various densities, and could be extremely valuable in early dental caries detection.

Near-infrared (NIR) dental imaging using scanning fiber endoscope (SFE) is being developed with advantages of miniature size (1.6mm), flexible shaft, video frame rate (7Hz), and expandable field of view (60 degrees). Using 1310, 1460, and 1550 nm laser diodes, the multispectral NIR SFE provides high contrast of lesion with transparency of stained and non-calcified plaque. However, capabilities of scanned NIR imaging remain unknown. Artificial interproximal lesions are created in extracted human posterior teeth by preparing a cavitation on the mesial or distal surface and then the cavitated artificial lesions were filled with hydroxyapatite powder and sealed with cyanoacrylate resin. Lesions are prepared at different occlusal-gingival depths from marginal ridges, lesion drilling depths and lesion size. Endoscopic reflectance images were acquired and compared to micro-CT scans and 1310 nm OCT images of the lesions to evaluate performance of the nirSFE. Results show that NIR SFE can image deep lesions under sound enamel with thickness of ≤4mm. All three wavelengths can detect deep lesions through the occlusal enamel which are not visible by naked-eye. 1460 nm has the highest contrast between lesion and sound enamel while 1310nm more clearly shows the contrast between enamel and dentin. Our nirSFE system can detect artificial interproximal lesions less than 4 mm below the occlusal surface, distinguish different drilling depth both in enamel and in dentin layer. Furthermore, the nirSFE realtime imaging and video functionality renders better lesion contrast and helps distinguish specular reflection and lesion signal. In conclusion, the NIR SFE has the potential to measure volume of these lesions due to the many viewing angles achievable by the miniature and flexible probe tip.

A novel strategy for the production of sintered ceramic dental implants is reported. The innovative and versatile 7-axes laser processing test bench makes the production of complex shapes with high precision possible. Quasitangential strategies prove an average deviation smaller 5 μm with a surface roughness R_a of 0.24 μm. The material is an yttria-stabilized alumina-toughened zirconia ceramic suited for biological applications subjected to load and wear. The heat-affected zone is negligible as shown by Raman spectroscopy. Following, this layer is laser ablated with an orthogonal strategy. Defined surface structures, like spots and grooves in the micrometer regime, are introduced for potential altered tissue interaction and enhanced osseointegration.

The mechanism of coffee eliciting erosion on teeth is unclear as few studies have investigated the direct effect of coffee on enamel and dentin structures. The present study identified how coffee, the most popular beverage worldwide, induces staining and erosion on teeth. We show the grade of erosion of molars and incisors in Sprague Dawley rats from two different age groups, young (four weeks) and old (six months). We quantified the concentration of metals contained in coffee by mass spectrometry (ICP-MS). To determine elemental content in enamel (i.e. superficial) and dentin (i.e. substructure), we used Laser-induced Breakdown Spectroscopy (LIBS) and X-ray fluorescence (XRF) spectroscopy, respectively. For LIBS, a significant decrease of Ca, P, and Na was observed in the young coffee group relative to agematched controls, whereas a significant increase in Mn, Fe, and K was observed. In the old coffee group, a significant increase of Mg, Fe, and K was observed along with a decrease of Mg, Ca, P, Na, Sr and Zn. For XRF, a significant decrease of the Ca/P ratio in the coffee group was observed. The SEM analysis showed pores and open spaces between young and old coffee groups, respectively. Thinning of enamel layers, loss of continuity in the enamel-dentin-junction, and wide spaces in dentin tubules with coffee use was found histologically. Coffee induces decalcification of teeth that corresponds to erosion, exposing the dentin structure by reducing enamel. Coffee immersion demonstrated an intrinsic staining in dentin by metal deposition.

Demineralized root dentin and cementum are mostly collagen that shrinks significantly upon dehydration. Active root caries lesions manifest shrinkage upon dehydration, however during the remineralization of root caries lesions mineral is deposited on the outside of the lesion arresting the lesion and arrested lesions no longer manifest shrinkage upon dehydration. Optical coherence tomography is ideally suited for the measurement of that shrinkage for the assessment of lesion activity. In this study the shrinkage of natural root caries lesions on extracted teeth were measured using a CP-OCT system with a 3D printed appliance with an integrated air nozzle suitable for clinical use.

Selective removal of dental calculus with high precision is best accomplished using lasers operating at high pulse repetition rates focused to a small spot size to limit damage to sound tissues. Conventional flashlamp pumped Er:YAG lasers are poorly suited for this purpose, but new diode-pumped solid state (DPSS) Er:YAG lasers have become available operating at high pulse repetition rates. The purpose of this study was to determine if image-guided laser ablation can be used to selectively remove calculus from tooth surfaces with minimal damage to the underlying sound cementum and dentin. A DPSS Er:YAG laser system was used to selectively remove calculus from ten extracted teeth using sequential SWIR images at 1500-1750-nm. The selectivity of removal was assessed using digital microscopy and optical coherence tomography. Calculus was removed with minimal damage to the underlying sound cementum and dentin.

It is challenging to identify demineralized areas of root lesions due to cervical erosion, calculus formation, and heavy staining of dentin. We have found that root caries can be imaged with extremely high contrast at short wavelength IR (SWIR) wavelengths beyond 1500-nm. Lasers are well suited for the selective removal of caries lesions from tooth surfaces. A CO₂ laser operating at a wavelength of 9.3-μm was combined with a thuliumdoped fiber laser operating at 1880-nm for the selective removal of root caries lesions from extracted teeth. Serial SWIR reflectance images at 1880-nm were used to guide the CO₂ laser for image-guided laser ablation. Cross polarization optical coherence tomography (CP-OCT) was used to assess the initial depth of the lesions before removal and assess the volume of sound and demineralized tissue removed by the CO₂ laser. With this image-guided approach, we believe we can achieve highly selective lesion removal and minimal damage to surrounding sound tissues.

Near Infrared Reflectance (NIR) is a new imaging technology that detects dental caries (decay) on tooth occlusal surfaces and in the interproximal contact sites between teeth. Conventional techniques, mostly dental x-rays, do not provide the high sensitivity and specificity at the vulnerable pits and fissure regions. The contrast of demineralization on tooth surfaces changes with increasing severity and the magnitude of that change with depth depends on the wavelength. The purpose of this study is to determine how the contrast changes with depth as a function of wavelength. Demineralization of varying depth was produced in 1.5 × 1.5 mm exposed windows after 1, 2, 3, 4, and 5 days of exposure to a demineralizing solution at pH 4.5. Lesions were imaged at 405, 630, 850, 1300, 1460, 1535, 1675, and 1950-nm with multiple imaging systems. The highest lesion contrast was measured at 1950-nm.