Christian Zakian

Near-infared hyperspectral imaging of teeth for dental caries detection

Near-infrared (NIR) is preferred for caries detection compared to visible light imaging because it exhibits low absorption by stain and deeper penetration into teeth. Hyperspectral images from 1000 to 2500 nm have been obtained for a total of 12 extracted teeth (premolars and molars) with different degrees of natural lesion. Analysis of the reflectance spectra suggests that light scattering by porous enamel and absorption by water in dentin can be used to quantify the lesion severity and generate a NIR caries score. Teeth were ground for histological examination after the measurements. The NIR caries score obtained correlates significantly (Spearmans correlation of 0.89, p<0.01) with the corresponding histological score. Results yield a sensitivity of >99% and a specificity of 87.5% for enamel lesions and a sensitivity of 80% and a specificity >99% for dentine lesions. The nature of the technique offers significant advantages, including the ability to map the lesion distribution rather than obtaining single-point measurements, it is also noninvasive, noncontact, and stain insensitive. These results suggest that NIR spectral imaging is a potential clinical technique for quantitative caries diagnosis and can determine the presence of occlusal enamel and dentin lesions.

In vitro performance of different methods in detecting occlusal caries lesions

UNLABELLED Early caries detection is essential for the implementation of preventive, therapeutic and intervention strategies within general dental practice. OBJECTIVE The aim of this study was to compare the in vitro performance of the International Caries Detection and Assessment System (ICDAS), digital photographs scored with ICDAS (ICDAS photographs), fibre-optic transillumination (FOTI), optical coherence tomography (OCT), SoproLife(®) camera and two implementations of quantitative light-induced fluorescence a commercial (QLF-Inspektor Research systems) and a custom (QLF-Custom) system, to detect early and intermediate occlusal lesions. METHODS One hundred and twelve permanent extracted teeth were selected and assessed with each detection method. Histological validation was used as a gold standard. The detection methods were compared by means of sensitivity, specificity, areas under receiver operating characteristic (AUROC) curves for enamel and dentine levels and with the Spearmans rank correlation coefficient against histology. RESULTS For any enamel or dentine caries detection, the AUROC curves ranged from 0.86 (OCT) to 0.98 (ICDAS and ICDAS photographs, SoproLife(®) camera) and at the dentine level from 0.83 (OCT) to 0.96 for FOTI. The correlations with histology ranged between 0.65 (OCT) and 0.88 (ICDAS and FOTI). Under in vitro conditions, the assessed detection methods showed excellent intra-examiner reproducibility. All the methods were strongly correlated with histology (p<0.01) except OCT which showed a moderate correlation (0.65). CONCLUSION Even though all methods present similar performance in detecting occlusal caries lesions, visual inspection seems to be sufficient to be used in clinical practice for detection and assessment of lesion depth. Other methods may be useful in monitoring caries lesion behaviour.

Particle sizing and flow measurement using self-mixing interferometry with a laser diode

New applications are presented for self-mixing interferometry, based on optical scattering, feedback and self-mixing in laser diodes. The self-mixing interferometry method has been developed for the determination of sub-micron particle sizes and for the measurement of flows in narrow diameter tubes. The rate equations for laser diodes subjected to frequency-shifted feedback are reviewed and extended to include a normalized frequency distribution to be characterized by the backscattered light spectrum. Experimental investigations are presented for (a) particle sizing using polystyrene particles in water from 0.02 to 0.20 mu m in diameter and (b) for transverse velocity profile determination using a 1.4 mm diameter tube with flow rates ranging between 10 and 100 ml h(-1). The observed frequency band increases for smaller particles when observing Brownian motion and for higher flow rates when observing flowing liquids. This experimental technique is inherently simple and low cost. Further potential applications of this technique include blood flow measurement in medicine, electrophoresis investigations in biology and particle characterization in process engineering and chemistry.

Occlusal caries detection by using thermal imaging.

OBJECTIVES To explore the applicability of thermal changes associated with dehydration for the detection and quantification of early tooth decay on occlusal surfaces using infrared imaging. METHODS A total of 72 sites on 25 human teeth with various degrees of natural demineralisation have been used. Continuous evaporation of water inside the pores by pressurised air-drying is used to produce a thermodynamic response on the tooth surface. The temporal profile of the temperature will depend on the amount of water at each position and this is studied in relation to the degree of porosity and the lesion severity. The area enclosed by the time-temperature curve, DeltaQ, was then used for quantification of the lesion. RESULTS Maps of DeltaQ were obtained and histological examinations were performed for all teeth. A detection sensitivity of 77% and specificity of 87% for areas that are either sound or have a histological E1 lesion, 87% and 72% for areas that have either an E2 or EDJ lesion, and 58% and 83% for areas that have a lesion reaching the dentin was found using this method. CONCLUSIONS Thermal imaging shows the ability to discriminate, in vitro, between (a) either areas that are sound or with a lesion on the outer half of the enamel and (b) areas with a lesion extending to the middle of the enamel or deeper. However, variations of the temperature in an open mouth and humidity due to respiration can potentially challenge the ability of using this technique in vivo and this requires further investigation.

Measuring initial enamel erosion with quantitative light-induced fluorescence and optical coherence tomography: an in vitro validation study.

Background: Measurement of initial enamel erosion is currently limited to in vitro methods. Optical coherence tomography (OCT) and quantitative light-induced fluorescence (QLF) have been used clinically to study advanced erosion. Little is known about their potential on initial enamel erosion. Objectives: To evaluate the sensitivity of QLF and OCT in detecting initial dental erosion in vitro. Methods: 12 human incisors were embedded in resin except for a window on the buccal surface. Bonding agent was applied to half of the window, creating an exposed and non-exposed area. Baseline measurements were taken with QLF, OCT and surface microhardness. Samples were immersed in orange juice for 60 min and measurements taken stepwise every 10 min. QLF was used to compare the loss of fluorescence between the two areas. The OCT system, OCS1300SS (Thorlabs Ltd.), was used to record the intensity of backscattered light of both areas. Multiple linear regression and paired t test were used to compare the change of the outcome measures. Results: All 3 instruments demonstrated significant dose responses with the erosive challenge interval (p < 0.05) and a detection threshold of 10 min from baseline. Thereafter, surface microhardness demonstrated significant changes after every 10 min of erosion, QLF at 4 erosive intervals (20, 40, 50 and 60 min) while OCT at only 2 (50 and 60 min). Conclusion: It can be concluded that OCT and QLF were able to detect demineralization after 10 min of erosive challenge and could be used to monitor the progression of demineralization of initial enamel erosion in vitro.

In vivo quantification of gingival inflammation using spectral imaging

Erythema is a reaction of the skin and oral soft tissues commonly associated with inflammation and an increase in blood flow. Diffuse reflection spectroscopy is a powerful tool for the assessment of skin inflammation where erythema has been linked to the relative concentration of oxygenated hemoglobin and blood perfusion. Here we demonstrate the applicability of a spectral imaging method for the quantification of gingival inflammation by looking at the gingival margin and papillary tip erythema. We present a longitudinal study on 22 healthy volunteers divided in two groups. The first was allowed to have normal oral hygiene and the second was subjected to an induced gingivitis for two weeks by cessation of oral hygiene. The spectral reflectance ratio at 615 and 460 nm, R(615)R(460), was proposed as a method to quantify and map the erythema spatial distribution. These wavelengths represent spectral absorption crossovers observed between oxygenated and deoxygenated hemoglobin. The spectral method presented shows a significant separation (p<0.01) between the groups when gingivitis was induced and correlates significantly (p<0.05) with the clinical gingival index scores. We believe that these investigations could contribute to the development of functional imaging methods for periodontal disease detection and monitoring.

Quantitative Light Fluorescence (QLF) and Polarized White Light (PWL) assessments of dental fluorosis in an epidemiological setting

BackgroundTo determine if a novel dual camera imaging system employing both polarized white light (PWL) and quantitative light induced fluorescence imaging (QLF) is appropriate for measuring enamel fluorosis in an epidemiological setting. The use of remote and objective scoring systems is of importance in fluorosis assessments due to the potential risk of examiner bias using clinical methods.MethodsSubjects were recruited from a panel previously characterized for fluorosis and caries to ensure a range of fluorosis presentation. A total of 164 children, aged 11 years (±1.3) participated following consent. Each child was examined using the novel imaging system, a traditional digital SLR camera, and clinically using the Dean’s and Thylstrup and Fejerskov (TF) Indices on the upper central and lateral incisors. Polarized white light and SLR images were scored for both Dean’s and TF indices by raters and fluorescence images were automatically scored using software.ResultsData from 164 children were available with a good distribution of fluorosis severity. The automated software analysis of QLF images demonstrated significant correlations with the clinical examinations for both Dean’s and TF index. Agreement (measured by weighted Kappa’s) between examiners scoring clinically, from polarized photographs and from SLR images ranged from 0.56 to 0.92.ConclusionsThe study suggests that the use of a digital imaging system to capture images for either automated software analysis, or remote assessment by raters is suitable for epidemiological work. The use of recorded images enables study archiving, assessment by multiple examiners, remote assessment and objectivity due to the blinding of subject status.

Dynamic light scattering by using self-mixing interferometry with a laser diode

The power spectrum of the laser intensity is studied when optical feedback in a laser diode is used as a sensing configuration for dynamic light-scattering experiments. We present a theory that relates the power spectrum obtained from standard dynamic light-scattering theory to the intensity power spectrum of the laser. This theory provides a concise description of this sensing technique, also known as self-mixing interferometry, when it is applied to Doppler shift and line-broadening measurements of the backscattered field.

Laser Doppler imaging through tissues phantoms by using self-mixing interferometry with a laser diode

Laser Doppler imaging has been widely used for the evaluation of cutaneous blood flow. We report on how the self-mixing interferometry configuration with a laser diode is explored for what is believed to be the first time to generate flow maps. The experiment was carried out by sensing the laser intensity power spectrum at each pixel as the laser was scanned over a model that mimics the properties of skin and circulating blood.

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 (Spearmans 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.