Characterization of dental caries by LIF spectroscopy with 404-nm excitation.

The potential of laser-induced fluorescence (LIF) spectroscopy for the characterization of different stages of dental caries using 404-nm diode laser excitation was investigated. In vitro spectra from 16 sound, 10 noncavitated carious and 10 cavitated carious molar teeth were recorded on a miniature fibre-optic spectrometer. The areas under the receiver operating characteristics (ROC-AUC) were calculated and one-way analysis of variance (ANOVA) was performed. The LIF spectra of the carious teeth showed two peaks at 635 and 680 nm in addition to a broad band seen at 500 nm in sound teeth. The fluorescence intensity ratios, F500/F635 and F500/F680, in carious teeth were always lower than those in sound teeth. The ROC-AUC for discriminating between carious and sound teeth was 0.94, and for discriminating between noncavitated and cavitated carious teeth was 0.87. Statistically significant differences (p<0.001) were seen between sound, noncavitated carious and cavitated carious teeth. The results showed that LIF spectroscopy has the potential to be useful for characterizing different stages of caries in a clinical setting.

In vivo temporal evolution of ALA-induced normalized fluorescence at different anatomical locations of oral cavity: application to improve cancer diagnostic contrast and potential.

BACKGROUND: The focal goal of this study is to identify optimal accumulation periods for ALA-induced PpIX in different healthy anatomical sites of human oral cavity and different types of abnormal mucosa to improve the accuracy of the clinical applications such as photodiagnosis and tissue grading. MATERIALS AND METHODS: Laser-induced fluorescence (LIF) emission spectra, with excitation at 404 nm from a diode laser, were recorded with a miniature fiber-optics spectrometer from 13 anatomical sites of oral mucosa in 15 healthy volunteers and 30 suspicious sites in 15 patients after topical application of 0.4% 5-ALA solution for 15 min. The optimal accumulation time in different anatomical sites of healthy subjects and abnormal tissues were determined by studying the temporal variation in normalized fluorescence intensities (NFI) at 635, 685 and 705 nm. RESULTS AND DISCUSSIONS: In masticatory anatomical locations such as (gingival and hard palate) and in lining mucosa (inner lip, soft palate, floor of mouth, transition to floor of mouth, alveolus and ventral tongue) except vermillion border of lip (VBL) of healthy subjects (designated as group I), it was observed that optimum time for maximum accumulation of PpIX is 90 min. In comparison, for lateral side of tongue (LST) and dorsal side of tongue (DST) tissues (designated as group II), maximum accumulation of PpIX was observed in 150 min of ALA application. For diverse grade lesions of group I mucosa in patients, maximum accumulation of PpIX was observed in 90 min, whereas, in group II mucosa the optimum accumulation time was 150 min as in the case of healthy mucosa. Further, between different grades oral mucosa, maximum variation in NFI take place at these optimal time periods. CONCLUSIONS: The determination of the optimum accumulation time of ALA in oral mucosa based on NFI helps to improve the diagnostic contrast and accuracy of oral cancer diagnosis, and to plan appropriate timing for ensuing PDT.

Clinical trial for detection of dental caries using laser-induced fluorescence ratio reference standard.

We present the clinical applicability of fluorescence ratio reference standard (FRRS) to discriminate different stages of dental caries. Toward this, laser-induced autofluorescence emission spectra are recorded in vivo in the 400- to 800-nm spectral range on a miniature fiber optic spectrometer from 65 patients, with a 404-nm diode laser as the excitation source. Autofluorescence spectra of sound teeth consist of a broad emission at 500 nm that is typical of natural enamel, whereas in caries teeth additional peaks are seen at 635 and 680 nm due to emission from porphyrin compounds in oral bacteria. Scatter plots are developed to differentiate sound teeth from enamel caries, sound teeth from dentinal caries, and enamel caries from dentinal caries using the mean fluorescence intensity (FI) and ratios F500F635 and F500F680 measured from 25 sites of sound teeth and 65 sites of carious teeth. The sensitivity and specificity of both the FI and FRRS are determined. It is observed that a diagnostic algorithm based on FRRS scatter plots is able to discriminate enamel caries from sound teeth, dentinal caries from sound teeth, and enamel from dentinal caries with overall sensitivities of 85, 100, and 88% and specificities of 90, 100, and 77%, respectively.

Clinical grading of oral mucosa by curve-fitting of corrected autofluorescence using diffuse reflectance spectra.

BACKGROUND: Laser-induced autofluorescence (LIAF) and diffuse reflectance (DR) were collectively used in this clinical study to improve early oral cancer diagnosis and tissue grading. METHODS: LIAF and DR emission from oral mucosa were recorded on a fiber-optic spectrometer by illumination with a 404-nm diode laser and tungsten halogen lamp in 36 healthy volunteers and 40 lesions of 20 patients. RESULTS: Absorption dips in LIAF spectra at 545 and 575 nm resulting from changes in oxygenated hemoglobin were corrected using DR spectra of the same site. These corrected spectra were curve-fitted using Gaussian spectral functions to determine constituent emission peaks and their relative contribution. The Gaussian peak intensity and area ratios F500/F635 and F500/F685 were found to be useful indicators of tissue transformation. The diagnostic capability of various ratios in differentiating healthy, hyperplastic, dysplastic, and squamous cell carcinomas (SCCs) were examined using discrimination scatterplots. CONCLUSIONS: The LIAF/DR technique, in conjunction with curve-fitting, differentiates different grades of dysplasia and SCC in this clinical trial and proves its potential for early detection of oral cavity cancer and tissue grading.

Oxygenated hemoglobin diffuse reflectance ratio for in vivo detection of oral pre-cancer.

Diffuse reflectance (DR) spectroscopy is a simple, low-cost, and noninvasive modality with potential for distinguishing oral precancer. Recently, in an ex vivo study, the DR spectral ratio (R545/R575) of oxygenated hemoglobin bands at 545 and 575 nm was used for grading malignancy. This work presents the results of clinical trials conducted in 29 patients to detect oral precancer using this ratio. We use site-specific normal spectra from a group of 36 healthy volunteers for comparison with those of patients. Toward this, in vivo DR spectra from 14 anatomical sites of the oral cavity of healthy volunteers are recorded on a miniature fiber optic spectrometer with white light excitation. The R545/R575 ratio is lowest for healthy tissues and appears to increase with the grade of malignancy. As compared to scatter plots that use the mean DR ratio from all anatomical sites, those using site-specific data show improved sensitivity and specificity for early diagnosis and grading of oral cancer. In the case of buccal mucosa, using scatter plots of R545/R575 ratio, we obtain a sensitivity of 100% and specificity of 86% for discriminating precancer (dysplasia) from hyperplasia, and a sensitivity of 97% and specificity of 86% for discriminating hyperplasia from normal.

Laser-induced autofluorescence spectral ratio reference standard for early discrimination of oral cancer.

BACKGROUND: Laser-induced autofluorescence (LIAF) is an emerging noninvasive technique in the biomedical field, especially for cancer detection. The goal of the study was to develop a spectral ratio reference standard (SRRS) to discriminate different grades of oral cancer. METHODS: LIAF emission spectra from oral mucosa were recorded in the 420-720 nm spectral range on a miniature fiberoptic spectrometer from 14 anatomical sites of 35 healthy volunteers and 91 sites of 44 patients, with excitation at 404 nm from a diode laser. RESULTS: Histopathologic analysis of biopsy samples showed that oral mucosa of adjoining malignant sites in patients are not usually normal, but showed various degrees of epithelial dysplasia and hyperplasia. Therefore, instead of using LIAF data from apparently normal lesions of patients as control, spectral data values of the oral mucosa of healthy volunteers were used as control. The autofluorescence emission at 500 nm is characteristic of oral mucosa, whereas in malignant lesions a new peak is seen at 685 nm in addition to the previously reported peaks at 635 and 705 nm. Three spectral ratio reference standard (SRRS) scatterplots were created to differentiate the normal mucosa from hyperplasia, hyperplasia from dysplasia, and dysplasia from squamous cell carcinoma (SCC) using the mean fluorescence intensity ratios (F500/F635, F500/705 and F500/F685) measured from 40 sites in 20 patients and 11 sites in 35 healthy volunteers. During blind tests at 21 sites in 17 patients all 3 SRRS plots showed 100% sensitivity and specificity to discriminate hyperplasia from dysplastic and normal tissues, whereas only the F500/F685 SRRS showed the same sensitivity and specificity to differentiate dysplasia from SCC. CONCLUSIONS: An SRRS criteria based on scatterplots of autofluorescence spectral intensity ratios is described to discriminate oral mucosal variations and screen early stages of tissue progression toward malignancy.

Tooth caries detection by curve fitting of laser-induced fluorescence emission: a comparative evaluation with reflectance spectroscopy.

BACKGROUND AND OBJECTIVES: Nitrogen laser-induced fluorescence (LIF) spectra of sound tooth consists of two broad bands centered at 440 and 490 nm, with two apparent side bands on either side. In order to locate the exact peak position of these bands and to effectively utilize the LIF spectral signatures for detection of tooth caries, the LIF spectra were curve-fitted using Gaussian spectral functions and the results were compared with those from diffuse reflectance spectral measurements. STUDY DESIGN/MATERIALS AND METHODS: The excitation light at 337.1 nm was guided to the sound and caries-affected tooth samples through the central fiber of the fiber-optic probe of a laser-induced fluorescence reflectance spectroscopy (LIFRS) system. Six surrounding fibers of the probe collect tooth fluorescence or diffuse reflectance from the lesion and direct it to a miniature spectrometer. The in vitro spectra were obtained from healthy enamel, dentin, and pulp level tooth caries. RESULTS: As compared to sound tooth, the caries tooth showed lower fluorescence and reflectance intensities in the 350-700 nm region. The deconvoluted peaks in the LIF spectra of sound tooth were found centered at 403.80, 434.20, 486.88, and 522.45 nm, whereas in the case of pulp level caries, a new peak was observed at 636.78 nm. Curve-fitted parameters, such as peak center, Gaussian curve area, full width at half intensity maximum (FWHM), and their ratios, were also found to vary with the stage of tooth caries. The ratios involving the 435 nm band, such as F405/F435, F435/F490, and F435/F525 ratios derived from curve-fitted areas and amplitudes, were found to be sensitive to discriminate between sound, dentin, and pulp level caries. Among the various diffuse reflectance spectral intensity ratios, the R500/R700 was found to be most sensitive to distinguish between pulp and dentin level caries. CONCLUSIONS: Nitrogen laser-excited fluorescence spectral studies were found to be more suited for detection of caries lesions. The LIF measurement with spectral analysis, done by curve fitting, outscores the diffuse reflectance methodology and shows the potential to screen different levels of tooth decay in a clinical setting.