Characterization of natural carious lesions by fluorescence spectroscopy at 405-nm excitation wavelength

We aim to characterize natural caries enamel lesions by fluorescence spectroscopy. Sixty human samples with natural noncavitated caries lesions on smooth surfaces were selected and classified into three groups: dull, shiny, and brown lesions. All the samples were analyzed externally at the natural surface and after hemisectionig internally at the center of the lesion. The lesions were excited with a 405-nm InGaN diode laser and the fluorescence was collected with a single grating spectrometer. Four emission bands (455, 500, 582, and 622 nm) are identified in both sound and carious regions. The area under each emission band is correlated with the total area of the four bands for the sound and carious regions. The detected fluorescence from natural and cut surfaces through the caries lesions is not statistically different for the shiny and dull lesion, but is different [analysis of variance (ANOVA) (p<0.05)] for brown lesion at all emission bands. At the 405-nm excitation wavelength, the area of the fluorescence bands at 455 and 500 nm differ statistically for natural carious lesions and sound tissue.     

Thermophotonic lock-in imaging of early demineralized and carious lesions in human teeth

As an extension of frequency-domain photothermal radiometry, a novel dental-imaging modality, thermophotonic lock-in imaging (TPLI), is introduced. This methodology uses photothermal wave principles and is capable of detecting early carious lesions and cracks on occlusal and approximal surfaces as well as early caries induced by artificial demineralizing solutions. The increased light scattering and absorption within early carious lesions increases the thermal-wave amplitude and shifts the thermal-wave centroid, producing contrast between the carious lesion and the intact enamel in both amplitude and phase images. Samples with artificial and natural occlusal and approximal caries were examined in this study. Thermophotonic effective detection depth is controlled by the modulation frequency according to the well-known concept of thermal diffusion length. TPLI phase images are emissivity normalized and therefore insensitive to the presence of stains. Amplitude images, on the other hand, provide integrated information from deeper enamel regions. It is concluded that the results of our noninvasive, noncontacting imaging methodology exhibit higher sensitivity to very early demineralization than dental radiographs and are in agreement with the destructive transverse microradiography mineral density profiles.     

Imaging caries lesions and lesion progression with polarization sensitive optical coherence tomography

New diagnostic tools are needed for the characterization of dental caries in the early stages of development. If carious lesions are detected early enough, they can be arrested without the need for surgical intervention. The objective of this study was to demonstrate that polarization sensitive optical coherence tomography (PS-OCT) can be used for the imaging of early caries lesions and for the monitoring of lesion progression over time. High-resolution polarization resolved images were acquired of natural caries lesions and simulated caries lesions of varying severity created over time periods of 1 to 14 days. Linearly polarized light was incident on the tooth samples and the reflected intensity in both orthogonal polarizations was measured. PS-OCT was invaluable for removing the confounding influence of surface reflections and native birefringence necessary for the enhanced resolution of the surface structure of caries lesions. This study demonstrated that PS-OCT is well suited for the imaging of interproximal and occlusal caries, early root caries, and for imaging decay under composite fillings. Longitudinal measurements of the reflected light intensity in the orthogonal polarization state from the area of simulated caries lesions linearly correlated with the square root of time of demineralization indicating that PS-OCT is well suited for monitoring changes in enamel mineralization over time.     

Remineralization of in vitro dental caries assessed with polarization-sensitive optical coherence tomography

Polarization-sensitive optical coherence tomography (PS-OCT) is potentially useful for imaging the nonsurgical remineralization of dental enamel. This study uses an all-fiber-based PS-OCT system operating at 1310 nm to image demineralized and fluoride-enhanced remineralized artificial lesions. PS-OCT images of lesions before and after remineralization are compared with the relative mineral loss DeltaZ (%vol x microm), obtained from high resolution digital microradiography (DM), and chemical composition changes by infrared spectroscopy. Severe early artificial caries show a significant increase in perpendicular-axis integrated reflectivity after remineralization. After sectioning the samples, DM demonstrates that the lesions remineralized with new mineral and the lesion surface zone show significant restoration of mineral volume. PS-OCT and DM both do not show a major change in lesion depth. For less severe artificial caries, the perpendicular-axis image resolves the scattering and depolarization of an outer growth layer after remineralization. This outer layer has a mineral volume close to that of sound enamel, and spectroscopic analysis indicates that the layer is a highly crystalline phase of apatite, without carbonate substitutions that increase the solubility of sound enamel. This study determines that PS-OCT can image the effects of fluoride-enhanced remineralization of mild and severe early artificial in vitro caries.     

Efficacy of bisphosphonates in detection of early enamel caries using NIR fluorescence imaging and inhibition of caries progression

NIR fluorescence imaging using bisphosphonate-Indocyanine green has been indicated for early interproximal caries detection. This study assessed diagnostic accuracy of caries detection by NIR fluorescence imaging with OsteoSense 750^® (OS750) in vitro and ex vivo, and to analyze the therapeutic efficacy of a bisphosphonate (Etidronate) in inhibiting enamel caries progression in vitro.Methods: Four experiments were conducted using extracted human teeth; 1) to calculate the infiltration rate of OS750 into interproximal white spot lesions using fluorescence microscope, 2) to assess diagnostic accuracy of interproximal natural white spot lesions using desktop NIR fluorescence imaging device in vitro setting, 3) to assess diagnostic accuracy of artificially created deeper enamel carious lesion (0.5 mm~1.0 mm) using NIR fluorescence image through the head-mount display in ex vivo setting, 4) to compare the progression on the enamel caries lesions treated by Etidronate, NaF and distilled-water. Diagnostic accuracy was analyzed using sensitivity, specificity and receiver operating curves (ROC). The caries progression was calculated with micro-CT and was statistically analyzed using a two-way ANOVA and the Tukey HDS post-hoc test.Results: 1) The infiltration rate of OS750 was 101.83% ± 8.66 (Min: 90.10%, Max: 133.94%). 2) The average of sensitivity and specificity in vitro setting experiments were 86.7% ± 4.4% and 70% ± 11%, respectively. The average of area under the ROC curves (AUC) was 0.883 ± 0.059 indicating excellent performance. 3) The mean sensitivity and specificity in ex vivo setting was 82.97% ± 15% and 76.78% ± 13.27% respectively. 4) The carious lesion volume treated by Etidronate was significantly smaller at post treatment-1 (p<0.05) and treatment-2 (p<0.01) than the control. There was no significant difference in lesion volume in the Etidronate and NaF group at the time point of post treatment-1.Conclusion: This study suggests that bisphosphonates contribute to both early diagnosis of enamel caries and inhibition of caries progression.     

Quantitative light-induced fluorescence: a potential tool for general dental assessment

Current dental diagnostic methods can detect caries but cannot quantify the mineral status of a lesion. Quantitative light-induced fluorescence (QLF) measures the percentage of fluorescence change of demineralized enamel with respect to surrounding sound enamel, and relates it directly to the amount of mineral lost during demineralization. Development of caries-like lesions and subsequent remineralization of the lesions were monitored by QLF. The results showed that the percentage of fluorescence change (Delta Q) increased linearly with the demineralization time and decreased with increased remineralization time. Stained teeth were whitened with a bleaching agent and the change in stain intensity (Delta E) was quantified using QLF. The results showed that Delta E decreased linearly as the tooth regained its natural color. Factors that might affect the use of QLF to detect and quantify caries were also examined. It was concluded that QLF could be used to detect and longitudinally monitor the progression or remineralization of incipient caries, however lesion detection may be limited by the presence of saliva or plaque and enhanced by staining. The change in shade of discolored teeth by whitening agents could be quantitatively measured by QLF.     

早期自然釉质龋光学相干断层图像定量分析

目的 通过对早期自然龋变光学相干断层成像(OCT)图像进行定量分析,寻找适于光学相干断层成像技术检测早期龋的定量参数指标.方法 选取D0期、D1期和D2期自然发生釉质龋双尖牙标本各3颗,利用光学相干断层成像分别对上述不同程度早期釉质龋人离体牙进行扫描,并以龋变区域(目标区域)平均灰度值与正常区域(背景区域)平均灰度之比...     

Histological validation of near-infrared reflectance multispectral imaging technique for caries detection and quantification

Near infrared (NIR) multispectral imaging is a novel noninvasive technique that maps and quantifies dental caries. The technique has the ability to reduce the confounding effect of stain present on teeth. The aim of this study was to develop and validate a quantitative NIR multispectral imaging system for caries detection and assessment against a histological reference standard. The proposed technique is based on spectral imaging at specific wavelengths in the range from 1000 to 1700 nm. A total of 112 extracted teeth (molars and premolars) were used and images of occlusal surfaces at different wavelengths were acquired. Three spectral reflectance images were combined to generate a quantitative lesion map of the tooth. The maximum value of the map at the corresponding histological section was used as the NIR caries score. The NIR caries score significantly correlated with the histological reference standard (Spearman's?Coefficient=0.774, p<0.01). Caries detection sensitivities and specificities of 72% and 91% for sound areas, 36% and 79% for lesions on the enamel, and 82% and 69% for lesions in dentin were found. These results suggest that NIR spectral imaging is a novel and promising method for the detection, quantification, and mapping of dental caries.     

渗透树脂在早期釉质龋修复中的应用：颜色稳定性评价

 背景：采用渗透树脂微创技术治疗釉质脱矿的修复效果优于传统的再矿化治疗,但目前研究渗透树脂修复非实质性缺损龋病后颜色变化的文献很少。目的：通过体外研究评估渗透树脂修复早期釉质龋的颜色稳定性。方法：将具有完整釉质面的48颗人离体牙浸泡在脱矿液中4周,制作成人工龋模型,之后进行渗透树脂修复,再随机均分成4组,分别置于红酒、咖啡、茶和人工唾液中浸泡2,4周。采用分光光度仪对病损区的颜色进行检测,以渗透树脂治疗后的检测作为基准色,计算出色差数值。结果与结论：浸泡后,4组样本都有不同程度的颜色变化。浸泡2周后,颜色变化大小顺序为：红酒>咖啡>茶>人工唾液,4组间比较差异有显著性意义(P < 0.05);浸泡4周后,颜色变化大小顺序为：红酒≈咖啡>茶>人工唾液,红酒组与咖啡组比较差异无显著性意义(P > 0.05),其他组间比较差异有显著性意义(P < 0.05)。红酒组与咖啡组浸泡不同时间点的颜色变化比较差异有显著性意义(P < 0.05)。浸泡在红酒、咖啡和茶一定的时间后,均显示在临床上不可以接受的色彩改变(?E >3.7)。说明渗透树脂颜色的稳定性受浸泡时间长短和浸泡溶液种类的影响,其中红酒、咖啡对其颜色稳定性影响较大,在人工唾液中颜色稳定性最好。 中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程     

In vitro detection and quantification of enamel and root caries using infrared photothermal radiometry and modulated luminescence

Artificially created demineralized and remineralized carious lesions on the root and enamel of human teeth were examined by photothermal radiometry (PTR) and modulated luminescence (LUM). Fourteen extracted human teeth were used and a lesion was created on a 1 mmx4 mm rectangular window, spanning root to enamel, using a lactic acid-based acidified gel to demineralize the tooth surface. The lesion was then exposed to a remineralization solution. Each sample was examined with PTR/LUM on the root and enamel before and after treatment at times from 1 to 10 (5 on root) days of demineralization and 2 to 10 days of remineralization. Ten-day (5 on root) demineralized samples were remineralized. After completing all the experiments, transverse microradiography (TMR) analysis was performed to compare and correlate the PTR/LUM signals to the depth of lesions and mineral losses. The PTR and LUM amplitudes and phases showed gradual and consistent changes with treatment time. In this study, TMR showed good correlation coefficients with PTR and LUM. It was also found that the length of the treatment time did not correlate very well to any technique, PTR/LUM or TMR, which implies a significant degree of inhomogeneity of the demireralization and remineralization rates in each and every tooth.     

Quantitative evaluation of the kinetics of human enamel simulated caries using photothermal radiometry and modulated luminescence

Photothermal radiometry and modulated luminescence (PTR-LUM) is an emerging nondestructive methodology applied toward the characterization and quantification of dental caries. We evaluate the efficacy of PTR-LUM in vitro to detect, monitor, and quantify human enamel caries. Artificial caries are created in extracted human molars (n = 15) using an acidified gel system (pH 4.5) for 10 or 40 days. PTR-LUM frequency scans (1 Hz-1 kHz) are performed before and during demineralization. Transverse microradiography (TMR) analysis, the current gold standard, follows at treatment conclusion to determine the mineral loss and depth of the artificially demineralized lesions. A theoretical model is applied to PTR experimental data to evaluate the changes in optothermophysical properties of demineralized enamel as a function of time. Higher optical scattering coefficients and poorer thermophysical properties are characteristic of the growing demineralized lesions, as verified by TMR, where the generated microporosities of the subsurface lesion confine the thermal-wave centroid. Enhanced optical scattering coefficients of demineralized lesions result in poorer luminescence yield due to scattering of both incident and converted luminescent photons. PTR-LUM sensitivity to changes in tooth mineralization coupled with opto-thermophysical property extraction illustrates the technique's potential for nondestructive quantification of enamel caries.     

Correlation of quantitative light-induced fluorescence and optical coherence tomography applied for detection and quantification of early dental caries

Fluorescence loss in enamel following demineralization has been correlated with the amount of mineral lost during the demineralization. The correlation between fluorescence loss measured by quantitative light-induced fluorescence (QLF) and the reflectivity loss measured by a versatile en face optical coherence tomography (OCT) system was investigated in a demineralization process to produce artificial dental caries. We used an OCT system that can collect A-scans (reflectivity versus depth), B-scans (longitudinal images), and C-scans (en face images). The power to the sample was 250 microW, the wavelength lambda = 850 nm, and the depth resolution in air 16 microm. A-scans, which show the profile of the reflectivity versus the depth of penetration into the tooth tissue, were used for quantitative analysis of the reflectivity loss. The results have shown that both the fluorescence radiance and reflectivity of the enamel decrease with increasing de- mineralization time. A linear correlation was observed between the percentage of fluorescence loss measured by QLF and the percentage of reflectivity loss measured by OCT. It was concluded that the decrease in reflectivity of the enamel during demineralization, measured by OCT, could be related to the amount of mineral lost during the de- mineralization process.     

A Scanning Electron Microscopic Study of Enamel Surfaces of Incipient Caries

The surface changes of natural incipient caries in human teeth were examined by scanning electron microscopy. Numerous small round depressions due to dissolved prism ends are observed. The prism sheaths seem to be preferentially demineralized, followed by demineralization of prism cores. Perikymata are well-pronounced. Focal holes and relatively large dissolution areas can be present. A new prismatic pattern of destruction with an appearance of fish scales is found. Evidence of remineralization of the incipient carious lesions is seen on the surfaces of the lesions. This study disagrees with the concept of an intact enamel surface layer.     

On the sensitivity of thermophotonic lock-in imaging and polarized Raman spectroscopy to early dental caries diagnosis

Dental caries is the leading cause of tooth loss, which can promptly be prevented if detected in early stages of progression. Unfortunately, conventional diagnostic modalities currently used in dentistry lack the sensitivity to detect early caries. The authors' intention is to compare the ability of polarized Raman spectroscopy and thermophotonic imaging to make early caries diagnosis. Extracted human teeth with no visible stain or defects were artificially demineralized in accordance to a well-known protocol in dentistry for simulated early caries development at several demineralization stages. Samples were then inspected using polarized Raman spectroscopy and thermophotonic imaging. The sensitivities of these two diagnostic modalities are compared, and the results are verified using transverse micro-radiography. It was found that compared to polarized Raman spectroscopy, thermophotonic imaging exhibits superior sensitivity to very early stages of demineralization.     

Nonintrusive, noncontacting frequency-domain photothermal radiometry and luminescence depth profilometry of carious and artificial subsurface lesions in human teeth

Nonintrusive, noncontacting frequency-domain photothermal radiometry (FD-PTR or PTR) and frequency-domain luminescence (FD-LUM or LUM) have been used with 659-nm and 830-nm laser sources to detect artificial and natural subsurface defects in human teeth. The major findings of this study are (1) PTR is sensitive to very deep (>5 mm) defects at low modulation frequencies (5 Hz). Both PTR and LUM amplitudes exhibit a peak at tooth thicknesses of ca. 1.4 to 2.7 mm. Furthermore, the LUM amplitude exhibits a small trough at ca. 2.5 to 3.5 mm. (2) PTR is sensitive to various defects such as a deep carious lesion, a demineralized area, an edge, a crack, and a surface stain, while LUM exhibits low sensitivity and spatial resolution. (3) PTR frequency scans over the surface of a fissure into demineralized enamel and dentin show higher amplitude than those for healthy teeth, as well as a pronounced curvature in both the amplitude and phase signal channels. These can be excellent markers for the diagnosis of subsurface carious lesions. (4) PTR amplitude frequency scans over the surface of enamels of variable thickness exhibit strong thickness dependence, thus establishing depth profilometric sensitivity to subsurface interfaces such as the dentin/enamel junction.     

自研全光纤光学相干计算机断层摄影术灵敏检测早期牙釉质龋

目的探索新型生物组织高分辨率成像技术——光学相干计算机断层摄影术（OCT）用于龋病早期诊断。方法选用化学酸蚀法在离体人恒牙釉质光滑面制备0、12、24、48、72、96、120h不同时间的早期脱矿人工龋模型,采用自行研发的口腔全光纤OCT（AF-OCT）进行离体人恒牙早期牙釉质人工龋的体外检测．并与同一牙齿样本的显微数码摄影、扫描电子显微镜和偏振光显微镜的检测结果进行比较．检验AF—OCT体外检测早期龋变的效能。结果AF—OCT可早期准确检测到脱矿12h以内的牙釉质表面组织学水平的改变．开窗区釉质表面脱矿深度与脱矿时间成正比。与3种常用体内外检测手段相比．AF—OCT可早于显微数码摄影观察到牙釉质表面的形貌改变．与扫描电子显微镜和偏振光显微镜检测结果高度相关。结论自研AF—OCT可早期、精确、无创地检测出脱矿12h以内的早期牙釉质表面人工龋变,并可实现量化测定和分析．获得的龋变深度量化测量数据与偏振光显微镜下组织学测量结果高度相关。     

Quantitative comparisons of potentially cariogenic microorganisms cultured from noncarious and carious root and coronal tooth surfaces.

Potentially cariogenic microorganisms cultured from noncarious and carious root and coronal (enamel) surfaces were quantitatively compared in patients 22 to 84 years of age (mean, 52 years). We collected 150 plaque specimens from 26 in situ teeth with initial root lesions and from 25 extracted teeth with advanced root lesions. The frequencies of isolation of Streptococcus mutans, Actinomyces viscosus, and Lactobacillus spp. were, respectively, 94, 72, and 51% at the noncarious root site; 98, 71, and 54% at the root lesion; 84, 61, and 44% at the noncarious enamel site; and 100, 66, and 90% at the enamel lesion. The streptococci made up the largest mean proportion of the total anaerobic cultivable microflora, ranging from 31.2% at the noncarious enamel site to 37.6% at the root lesion, while S. mutans varied between 18% at the noncarious enamel and root surfaces and approximately 24% at both the enamel and root lesions. The proportion of actinomyces ranged from 12.3% at the root lesion to 23.6% at the noncarious root site, while A. viscosus varied from 7.8% at the root lesion to 15.1% at the noncarious root site. The largest mean proportion of lactobacilli (4.2%) was recovered at the enamel lesion site. Proportions of Candida spp. made up less than 0.1% at all sites. Proportions of microorganisms did not differ significantly between noncarious enamel and root sites, but the noncarious coronal and root sites had higher (P less than 0.05) proportions of actinomyces than did the root lesion. Also, enamel lesions had a greater (P less than 0.05) percentage of Lactobacillus spp. than did root lesions. The number of streptococci recovered from the root lesion was greater (P less than 0.01) than the number of actinomyces at the same site. S. mutans was recovered from initial root lesions in greater numbers (P less than 0.001) than were actinomyces and lactobacilli. The number of S. mutans recovered at the initial root lesions was greater (P less than 0.01) than that recovered from the advanced root lesions.     

Light scattering properties of natural and artificially demineralized dental enamel at 1310 nm

A fundamental understanding of how near-IR light propagates through sound and carious dental hard tissues is essential for the development of clinically useful optical diagnostic systems, since image contrast is based on changes in the optical properties of these tissues on demineralization. During the caries (decay) process, micropores are formed in the lesion due to partial dissolution of the individual mineral crystals. Such small pores behave as scattering centers, strongly scattering visible and near-IR light. The optical properties of enamel can be quantitatively described by the absorption and scattering coefficients, and the scattering phase function. Our aim is to measure the optical scattering behavior of natural and artificial enamel caries. Near-IR attenuation measurements and angular-resolved goniometer measurements coupled with Monte Carlo simulations are used to determine changes in the scattering coefficient and the scattering anisotropy on demineralization at 1310 nm. An ultra-high resolution digital microradiography system is used to quantify the lesion severity by measurement of the relative mineral loss for comparison with optical scattering measurements. The scattering coefficient increases exponentially with increasing mineral loss. Natural and artificial demineralization increases the scattering coefficient more than two orders of magnitude at 1310 nm, and the scattering is highly forward directed.     

Prospects for applying fluorescence spectroscopy to diagnose the hard tissues of a tooth

This article deals with the autofluorescence spectra from the hard tissues of a tooth, both in norm and pathology. An investigation was made on 30 extracted human teeth. The measurements were made both for the intact hard tissues of a tooth, such as enamel, dentine, cementum, and root canal, and for the tissues pathologically affected by a caries (superficial, intermediate, and deep) and by a dental calculus. It was found that the fluorescent spectra from enamel, dentine, cementum, and from the regions affected by a caries and dental calculus were identical in form. All the spectra revealed a maximum near 700 nm. However, the intact and affected hard tissues were greatly different in the integral fluorescent intensity. Dental calculus was found to produce the most pronounced fluorescent intensity, whereas the carious regions produced a slightly weaker fluorescent intensity. On the contrary, the intact hard tissues of a tooth exhibited the poorest fluorescent intensity.     

Imaging artificial caries under composite sealants and restorations

Polarization-sensitive optical coherence tomography (PS-OCT) is used to monitor the progression of simulated caries lesions on occlusal surfaces and image the lesions underneath composite sealants. The polarization-sensitive system, recording images in both the parallel and perpendicular axes, is useful for enhancing the image contrast of the artificial caries and minimizing the interference of the strong reflections at surface interfaces. Using the perpendicular-axis signal, the mean reflectivity increase from day 0 to day 14 is 5.1 dB (p<0.01, repeated-measures analysis of variation, Tukey-Kramer). For imaging lesions underneath the sealants, the mean reflectivity of the enamel underneath 250, 500, 750, and 1000 microm of composite is calculated for demineralized and control samples. The artificial lesions can be detected under 750 microm of visibly opaque sealant, with a 5.0-dB difference from the control samples (t-test, p<0.001). Tooth colored sealants allow deeper imaging depth. The artificial lesions could be detected under 1000 microm of sealant, with a 6.6-dB difference from the control samples (t-test, p<0.001). This study demonstrates that PS-OCT can be used to track lesion progression on occlusal surfaces nondestructively with or without sealants.