Diagnosis and staging of caries using spectral factors derived from the blue laser-induced autofluorescence spectrum

Teeth Microcracks Research: Towards Multi-Modal Imaging

This perspective is an overview of the recent advances in teeth microcrack (MC) research, where there is a clear tendency towards a shift from two-dimensional (2D) to three-dimensional (3D) examination techniques, enhanced with artificial intelligence models for data processing and image acquisition. X-ray micro-computed tomography combined with machine learning allows 3D characterization of all spatially resolved cracks, despite the locations within the tooth in which they begin and extend, and the arrangement of MCs and their structural properties. With photoluminescence and micro-/nano-Raman spectroscopy, optical properties and chemical and elemental composition of the material can be evaluated, thus helping to assess the structural integrity of the tooth at the MC site. Approaching tooth samples having cracks from different perspectives and using complementary laboratory techniques, there is a natural progression from 3D to multi-modal imaging, where the volumetric (passive: dimensions) information of the tooth sample can be supplemented by dynamic (active: composition, interaction) image data. Revelation of tooth cracks clearly shows the need to re-assess the role of these MCs and their effect on the structural integrity and longevity of the tooth. This provides insight into the nature of cracks in natural hard materials and contributes to a better understanding of how bio-inspired structures could be designed to foresee crack propagation in biosolids.

Applications of Laser-Induced Fluorescence in Medicine

Fluorescence is the most sensitive spectroscopic method of analysis and fluorescence methods. However, classical analysis requires sampling. There are new needs for real-time analyses of biological materials, without the need for sampling. This article presents examples of proprietary applications of laser-induced fluorescence (LIF) in medicine with such methods. A classic example is the analysis of photosensitizers using the photodynamic treatment method (PDT). The level and kinetics of accumulation and excretion of sensitizers in the body are examined, as well as the optimal exposure time after the application of compounds. The LIF method is also used to analyze endogenous fluorophores; it has been used to detect neoplasms, e.g., lung cancer or gynecological and dermatological diseases. Furthermore, it is used for the diagnosis of early stages of tooth decay or detection of fungi. The article will present the construction of sensors based on the LIF method—fiber laser spectrometers and investigated fluorescence spectra in individual applications. Examples of fluorescence imaging, e.g., dermatological, and dental diagnostics and measuring systems will be presented. The advantage of the method is it has greater sensitivity and easily detects lesions early compared to the methods used in observing the material in reflected light.

Color masking prediction of posterior white spot lesions by resin infiltration in vitro

OBJECTIVE

To investigate parameters that could predict the color masking effect (ME) of white spot lesions (WSLs) after resin infiltration (RI).

METHODS

Sixty extracted human teeth with natural WSLs were selected (28 premolars, 29 molars and 3 incisors). At baseline, the laser fluorescence (LF) of surrounding sound enamel (SE) and the WSLs were analyzed with DIAGNOdent. Standardized photographs were obtained under D65 and UV illuminants, from which the CIE L*a*b* color coordinates and natural fluorescence (NF) of the WSLs and SE were obtained. The color difference (ΔE₀₀) and differences of NF and LF between the SE and WSLs were calculated. The lesion dimensions (area, perimeter, width, and height) were determined. After RI, the assessments were repeated. ME was considered as the reduction of ΔE₀₀ values after RI. One-way ANOVA and the Tukey tests were used to analyze the absolute means of the LF and NF values. The t test was used to compare the ΔE₀₀ values and lesion dimensions before and after infiltration. The correlations between all parameters at baseline and ME were analyzed.

RESULTS

The absolute mean values of LF at the baseline (B) and after infiltration (I) were SE/B-3.98a, WSL/B-13.28c, SE/I-3.36a, WSL/I-7.95b (p = 0.001). The mean values for NF were SE/B-7.93a; WSL/B-6.29b, SE/I-7.93a, WSL/I-7.27a (p = 0.001). The results for ΔE₀₀ were B-11.74a, I-8.66b (p = 0.001). RI significantly reduced lesion dimensions. No correlations were observed between the baseline parameters and the ME.

CONCLUSIONS

The WSLs presented higher LF and smaller NF than SE, which were respectively reduced and increased after RI. Prediction of the masking effect by the parameters evaluated at baseline was not possible, which could be due to the choice of mainly caries lesions in posterior teeth. Nonetheless, infiltration was found suitable to mask most of the WSL.

CLINICAL SIGNIFICANCE

The color masking effect of white spot lesions after resin infiltration cannot be predicted by a previous analysis of fluorescence, color, or dimensions of the lesion.

Spectral characteristics of caries autofluorescence obtained from different locations and caries severities

Dental caries usually occurs at interproximal and occlusal surfaces. The purpose of the present study was to determine if characteristic spectral factors extracted from autofluorescence (AF) spectra are informative regarding caries detection and the determination of caries stage as compared with DIAGNOdent results. AF spectra were obtained from caries lesions of different severities at two locations using a 405 nm laser. Three spectral factors, that is, spectral slope at 550 to 600 nm, spectral area under the curve at 500 to 590 nm and two-peak ratio between 625 and 667 nm, were extracted. The values of three spectral factors linearly decreased as caries progressed. According to micro-CT images, conventional visual and tactile inspections of lesions under or overestimated (25%-65%) caries states, and brown or thickly stained layer on interproximal or occlusal surfaces, respectively, caused misclassifications of caries stage. Of the spectral factors examined, spectral slope and area under curve for interproximal and occlusal surfaces, respectively, were found to be significantly related to caries stage and showed least data overlap. For interproximal and occlusal surfaces, DIAGNOdent readings of different stages overlapped considerably though their mean values were significantly different regardless of stage.