Polarization memory effect in optical coherence tomography and dental imaging application.

We report the existence of polarization memory effect (PME) in optical coherence tomography and investigate its potential applications in dental imaging. We performed the study in three steps. First, microsphere scattering phantoms of different sizes were imaged in order to validate experimental results with PME theory. Both linearly and circularly polarized light were used to probe the samples. Second, healthy tooth samples were scanned and polarization memory effect was identified in dentin. In this step, specific verification and signal processing were performed to rule out possible image interpretation by birefringence effect. Third, we evaluated dentin demineralization with PME. Results show polarization memory can be useful to characterize this dynamic mineralization process for early caries detection and rehabilitation.

Actinobacillus actinomycetemcomitans leukotoxin requires lipid microdomains for target cell cytotoxicity.

Actinobacillus actinomycetemcomitans produces a leukotoxin (Ltx) that kills leukocyte function-associated antigen-1 (LFA-1)-bearing cells from man, the Great Apes and Old World monkeys. The unique specificity of Ltx for the beta2 integrin, LFA-1, suggests it is capable of providing insight into the pathogenic mechanisms of Ltx and other RTX toxins. Using the Jurkat T cell line and an LFA-1-deficient Jurkat mutant (Jbeta2.7) as models, we found the initial effect of Ltx is to elevate cytosolic Ca2+ [Ca2+]c, an event that is independent of the Ltx/LFA-1 interaction. [Ca2+]c increases initiate a series of events that involve the activation of calpain, talin cleavage, mobilization to, and subsequent clustering of, LFA-1 in cholesterol and sphingolipid-rich regions of the plasma membrane known as lipid rafts. The association of Ltx and LFA-1 within lipid rafts is essential for cell lysis. Jbeta2.7 cells fail to accumulate Ltx in their raft fractions and are not killed, while cholesterol depletion experiments demonstrate the necessity of raft integrity for Ltx function. We propose that toxin-induced Ca2+ fluxes mobilize LFA-1 to lipid rafts where it associates with Ltx. These findings suggest that Ltx utilizes the raft to stimulate an integrin signalling pathway that leads to apoptosis of target cells.

Cholesterol-rich membrane microdomains mediate cell cycle arrest induced by Actinobacillus actinomycetemcomitans cytolethal-distending toxin.

We have previously shown that Actinobacillus actinomycetemcomitans cytolethal-distending toxin (Cdt) is a potent immunosuppressive agent that induces G2/M arrest in human lymphocytes. In this study, we explored the possibility that Cdt-mediated immunotoxicity involves lipid membrane microdomains. We first determined that following treatment of Jurkat cells with Cdt holotoxin all three Cdt subunits localize to these microdomains. Laser confocal microscopy was employed to colocalize the subunits with GM1-enriched membrane regions which are characteristic of membrane rafts. Western blot analysis of isolated lipid rafts also demonstrated the presence of Cdt peptides. Cholesterol depletion, using methyl beta-cyclodextrin, protected cells from the ability of the Cdt holotoxin to induce G2 arrest. Moreover, cholesterol depletion reduced the ability of the toxin to associate with Jurkat cells. Thus, lipid raft integrity is vital to the action of Cdt on host cells. The implications of our observations with respect to Cdt mode of action are discussed.

Chondrocytes utilize a cholesterol-dependent lipid translocator to externalize phosphatidylserine.

During endochondral ossification, growth plate chondrocytes release plasma membrane (PM) derived matrix vesicles (MV), which are the site of initial hydroxyapatite crystal formation. MV constituents which facilitate the mineralization process include the integral membrane ectoenzymes alkaline phosphatase (ALPase) and nucleotide pyrophosphatase phosphodiesterase (NPP1/PC-1), along with a phosphatidylserine- (PS-) rich membrane surface that binds annexins and calcium, resulting in enhanced calcium entry into MV. In this study, we determined that chick growth plate MV were highly enriched in membrane raft microdomains containing high levels of cholesterol, glycophosphatidylinositol- (GPI-) anchored ALPase, and phosphatidylserine (PS) localized to the external leaflet of the bilayer. To determine how such membrane microdomains arise during chondrocyte maturation, we explored the role of PM cholesterol-dependent lipid assemblies in regulating the activities of lipid translocators involved in the externalization of PS. We first isolated and determined the composition of detergent-resistant membranes (DRMs) from chondrocyte PM. DRMs isolated from chondrocyte PM were enhanced in ganglioside 1 (GM1) and cholesterol as well as GPI-anchored ALPase. Furthermore, these membrane domains were enriched in PS (localized to the external leaflet of the bilayer) and had significantly higher ALPase activity than non-cholesterol-enriched domains. To understand the role of cholesterol-dependent lipid assemblies in the externalization of PS, we measured the activities of two lipid transporters involved in PS externalization, aminophospholipid translocase (APLT) and phospholipid scramblase (PLSCR1), during maturation of a murine chondrocytic cell line, N1511. In this report, we provide the first evidence that maturing chondrocytes express PLSCR1 and have scramblase activity. We propose that redistribution of PS is dependent on an increase in phospholipid scramblase activity and a decrease in APLT activity. Lastly, we show that translocator activity is most likely to be modulated by membrane cholesterol levels through a membrane raft microdomain.

E2F4 expression patterns in SIV encephalitis.

The E2F1 transcriptional regulator has been shown to exhibit altered expression and localization in HIVE and SIVE. However, other E2F family members are expressed in mature neurons and participate in neuronal differentiation. In an in vitro model of neuronal differentiation, E2F4 protein levels have been shown to increase. Further reduction in E2F4 leads to loss of neurites in this model. Neuritic damage and loss are also seen in progression of HIVE and SIVE. To determine if changes in E2F4 may contribute to altered neuronal morphology and survival, we assessed E2F4 immunostaining in caudate and mid-frontal cortex from SIVE macaques and non-encephalitic controls. We found that E2F4 was expressed in neurons and localized to nuclei in both SIVE and non-encephalitic controls. Quantification of E2F4 fluorescence intensity indicated that there was an overall decrease in E2F4 in caudate of SIVE macaques as compared to non-encephalitic controls, which correlated with a decrease in the neuronal phenotypic marker, MAP2. In contrast, we observed a slight increase in E2F4 in mid-frontal cortex of SIVE despite a significant decrease in MAP2. When E2F4 is normalized to MAP2, we found an increase in E2F4 fluorescence intensity per MAP2 in SIVE mid-frontal cortex. These findings suggest changes in E2F4 may be contributing to altered neuronal morphology or survival in SIVE.

Assessing the accuracy of caries diagnosis via radiograph. Film versus print.

BACKGROUND: The authors conducted this study to determine if proximal caries diagnoses made using bitewing radiographic images printed on photographic paper were comparable with diagnoses made using traditional radiographic film images. METHODS: The authors digitized 15 posterior bitewing radiographs that contained 74 carious and 127 sound unrestored proximal surfaces and printed them on photographic paper. Fourteen dentists evaluated the radiographs and two printed image formats (4 x 3 centimeters and 8 x 6 cm) for evidence of caries. The diagnostic accuracy and interobserver agreement for caries diagnoses obtained in the two printed image formats were compared with those for radiographic film images. RESULTS: Overall, the diagnostic accuracy of printed images did not differ significantly from radiographic film images for dentinal caries. However, for caries limited to the enamel surface, a decrease in sensitivity was noted in six of the 14 observers for the smaller print images, while no significant differences in the diagnoses of enamel caries were observed among any of the observers in the enlarged print format. CONCLUSION: This study provides evidence that printed images can be used to diagnose dental caries reliably. CLINICAL IMPLICATIONS: The results of this study indicate that the diagnostic information obtained by viewing printed images is equivalent to that obtained by viewing standard radiographs. Size of the printed image also may be important in caries diagnosis and care must be taken to print bitewing radiographic images at a size that optimizes interpretation. Other factors that must be considered are the type of printer, printer resolution, paper quality and type of ink used. With careful consideration of printing parameters, clinicians can be assured of diagnostic quality in printed images.

Characterization of dentin, enamel, and carious lesions by a polarization-sensitive optical coherence tomography system.

Enamel and dentin are the primary components of human teeth. Both of them have a strong polarization effect. We designed a polarization-sensitive optical coherence tomography (PSOCT) system to study the spatially resolved scattering and polarization phenomena of teeth. The system is constructed in free space to avoid the complexity of polarization control in fiber-based PSOCT. The structural features of enamel were evaluated in five human teeth that had no visible evidence of caries. The teeth were subsequently sectioned in mesial distal orientation and coronal orientation. Then the structural aspects of dentin were evaluated. OCT images were made of the mantel dentin near the dentin-enamel junction. Five teeth with interproximal and occlusal caries were also studied. With two channel and phase-retardation images, PSOCT provided better functional contrast and more detailed structural information than conventional OCT. For a better description of the measured PSOCT data, we classify these features by two types, i.e., the local textural features and the global structural features. This study indicates that PSOCT has the potential to be a powerful tool for research of dental formation and caries diagnosis.

Fetal Alz-50 clone 1 interacts with the human orthologue of the Kelch-like Ech-associated protein.

The fetal Alz-50 reactive clone 1 (FAC1) protein exhibits altered expression and subcellular localization during neuronal development and neurodegenerative diseases such as Alzheimer's disease. Using the yeast two-hybrid screen, the human orthologue of Keap1 (hKeap1) was identified as a FAC1 interacting protein. Keap1 is an important regulator of the oxidative stress response pathway through its interaction with the Nrf family of transcription factors. An interaction between full-length FAC1 and hKeap1 proteins has been demonstrated, and the FAC1 binding domain of hKeap1 has been identified as the Kelch repeats. In addition, FAC1 colocalizes with endogenous Keap1 within the cytoplasm of PT67 cells. Exogenously introduced eGFP:hKeap1 fusion protein redistributed FAC1 to colocalize with eGFP:hKeap1 in perinuclear, spherical structures. The interaction between FAC1 and hKeap1 is reduced by competition with the Nrf2 protein. However, competition by Nrf2 for hKeap1 is reduced by diethylmaleate (DEM), a known disrupter of the Nrf2:Keap1 interaction. DEM does not affect the ability of FAC1 to bind hKeap1 in our assay. These results suggest that hKeap1 regulates FAC1 in addition to its known role in control of Nrf2. Furthermore, the observed competition between FAC1 and Nrf2 for binding hKeap1 indicates that the interplay between these three proteins has important implications for neuronal response to oxidative stress.

Bone structure effect on root resorption.

OBJECTIVES: To explore if alveolar bone shape and density might promote external apical root resorption. SETTING AND SAMPLE POPULATION: Panoramic radiographs of 700 patients who had orthodontic treatment at Temple University were reviewed and 22 patients with radiographic evidence of root resorption on the lower incisors were selected for the study. Exclusion criteria included a history of systemic diseases, craniofacial abnormalities, tooth injury, endodontically treated teeth, and impacted teeth. METHODS: Pre-treatment (T1) and post-treatment (T2) cephalometric radiographs were converted into digital format and enhanced to reduce contrast variability and improve edge definition. Tooth length, root length, root area, alveolar area around the root including cortical area, area of medullary bone, and area of the symphysis were measured using an interactive software algorithm. A region of interest within the symphysis was also defined and trabecular space area and fractal dimension calculated as an estimate of bone density. RESULTS: Root area and tooth length were correlated negatively with changes in root area, tooth area, and root length. Larger teeth demonstrated a greater amount of root resorption. Dentoalveolar complex dimensions remained relatively unchanged during tooth movement. The amount of alveolar bone around the root, thickness of cortical bone, density of the trabecular network, and fractal dimension showed no significant correlation with the extent of the external apical root resorption. CONCLUSIONS: The results of this study suggest that the density and morphology of the dentoalveolar complex are not significant factors in the etiology of external apical root resorption.

Quantifying labial blood flow using optical Doppler tomography.

OBJECTIVES: Changes in the oral microvasculature occur in a variety of diseases. Optical Doppler tomography (ODT) combines laser Doppler flowmetry with optical coherence tomography (OCT) to produce high-resolution tomographic images of biological tissues that also detect the velocity and direction of blood flow. The objective of this study was to determine the feasibility of ODT to image labial blood flow. A prototype ODT imaging system was constructed that characterized and measured labial blood flow in healthy subjects. MATERIALS AND METHODS: A prototype ODT instrument was constructed using a diode light source with a central wavelength of 1300 nanometers, a 40-nanometer spectral width and 2.4 microwatts output power. To verify the accuracy of the system, the flow rates of a phantom material (Intralipid) pumped through a capillary tube at various speeds was measured. To evaluate the clinical feasibility of the ODT prototye, the mucosal aspect of the upper and lower lips at the midline was imaged in 9 healthy volunteers. The sample arm of the instrument consisted of a fiberoptic probe with a 2-mm in diameter polished glass lens attached to the end. The probe was placed approximately 3 mm from the mucosal surface of the lip and oriented perpendicular to the surface. A motorized translation stage moved the fiber in a superior to inferior direction while the subject's head was stabilized by placing the chin into a chin rest. Imaging time for a 12-mm x 2.5-mm scan was approximately 64 seconds. RESULTS: The phantom experiments revealed that accuracy of this novel ODT prototype to measure flow was within 5%. In vivo labial blood flow velocity ranged from 11.8 to 43.1 mm/second in the upper lip and 8.2 to 53.2 mm/second in the lower lip. There were no statistically significant differences between flow rates in the upper and lower lips. OCT images and Doppler velocity signals were successfully integrated producing in vivo images of labial blood in all of the subjects (15 images). The resulting cross-sectional images revealed microscopic details of labial structures and, to the best of our knowledge, are the first ODT images of the labial microvasculature. CONCLUSIONS: The results of this in vivo study prove the feasibility of ODT to quantify labial blood flow and produce high spatial resolution images specifically localizing vessels anatomically. ODT provides both flow speed and flow direction information. ODT is noninvasive and offers the advantages of high volumetric flow sensitivity.

Quantifying enamel luster.

OBJECTIVE: When the pH of the oral cavity drops below 5.5, the hydroxyapatite crystalline lattice is damaged and the tooth surface becomes rough. Consequently, specular reflection is decreased and results, clinically, in a loss of tooth luster. The aim of this study was to develop a digital image capture and processing algorithm to quantify enamel luster. METHODOLOGY: Extracted human teeth (n = 25) containing no restorations and with no clinical evidence of caries were used in this study. The teeth were sectioned longitudinally in a mesial-to-distal orientation to provide experimental and control groups. The experimental group was treated with six consecutive 60-minute exposures to an acidic soft drink, separated by tap water rinses; the control group was similarly treated with just the tap water. Standardized photographs were made before and after application of the treatment or control conditions. Images were converted to eight-bit monochrome digital format. The clinical crown was identified using a standard digital masking technique. Luster in the crown was quantified by determining pixels with luminescence values that were 65% above background. RESULTS: Overall, there was an average 53.6% change in luster in the experimental group, and a nominal 2.10% change in luster in the control group. Analysis of variance revealed a significant loss in luster as measured by this algorithm in the experimental group (p < 0.001), while no significant change in luster was found in the control group. The method reliably identified luster with a repeatability coefficient of 0.992. CONCLUSION: Our digital processing algorithm consistently quantified loss of enamel luster associated with exposure to an acidic beverage. This digit photographic technique may be valuable for evaluating changes in the esthetic chacteristics of teeth when they are exposed to a variety of adverse environments.

Doppler angle and flow velocity mapping by combined Doppler shift and Doppler bandwidth measurements in optical Doppler tomography.

Accurate estimation of flow velocity requires measurement of Doppler angle, which is not available in general clinical applications. We describe a novel method of direct Doppler angle and flow velocity mapping that uses a conventional single-beam optical Doppler tomography system. The Doppler angle is estimated by combination of Doppler shift and Doppler bandwidth measurements, and flow velocity is calculated from the Doppler shift and the estimated Doppler angle. In vivo study of lip microvascularization demonstrates that this method is capable of providing both flow speed and flow direction information.

Identification of occlusal sealants using optical coherence tomography.

OBJECTIVE: Optical coherence tomography (OCT) is a new imaging technique that uses light to image dental structures interferometrically. OCT creates cross-sectional images that have potential diagnostic value for dental applications. When used in epidemiological studies, OCT offers a safe, non-invasive technique to discriminate occlusal sealants and composite restorations. This paper summarizes a study in which dentists were asked to interpret and discriminate between OCT images. METHODOLOGY: Twenty-one dentists were asked to interpret OCT images of nine extracted premolars that were either not restored, contained an occlusal sealant or were restored with a composite restoration. RESULTS: Although the dentists were previously unfamiliar with OCT images, they adapted well and felt confident in their diagnoses using this new technology. The sensitivity of OCT to discriminate composite and sealants was > 0.92, while the specificity of discrimination was > 0.94. The capacity of OCT to discriminate sealants from non-restored occlusal surfaces was slightly less (sensitivity 0.88; specificity 0.86), but still within a clinically acceptable level. Inter- and intra-rater reliability, as measured by the kappa statistic, also revealed excellent performance by dentists using this new imaging technology. Intra-rater reliability was very good, ranging from 0.82 to 1.0. Inter-rater reliability was also high, predominately in the "Good" to "Very Good" agreement range. CONCLUSION: This preliminary study indicates OCT imaging may be an important new technology for discriminating occlusal sealants and composite restorations.

Quantitative assessment of flow velocity-estimation algorithms for optical Doppler tomography imaging.

We present a quantitative comparison of three categories of velocity estimation algorithms, including centroid techniques (the adaptive centroid technique and the weighted centroid technique), the sliding-window filtering technique, and correlation techniques (autocorrelation and cross correlation). We introduce, among these five algorithms, two new algorithms: weighted centroid and sliding-window filtering. Simulations and in vivo blood flow data are used to assess the velocity estimation accuracies of these algorithms. These comparisons demonstrate that the sliding-window filtering technique is superior to the other techniques in terms of velocity estimation accuracy and robustness to noise.

Undiagnosed multiple myeloma causing extensive dental bleeding: report of a case and review.

A case of multiple myeloma causing profuse bleeding during a minor dental surgical procedure is presented. The value of dental radiography in detection of bone changes associated with an undiagnosed case of multiple myeloma is highlighted. We show that the extensive bleeding during the dental procedure could have been prevented if the panoramic radiograph had been evaluated carefully before initiation of the treatment. In addition, we briefly discuss the etiologic factors responsible for the formation of hemostatic abnormalities in multiple myeloma and the value of imaging methods used in diagnostic assessment of the disease.