Light-based diagnostic methods for the in vivo assessment of initial caries lesions: Laser fluorescence, QLF and OCT.

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To evaluate different light-based caries diagnostic methods for assessment of non-cavitated initial carious lesions on smooth surfaces. 39 participants were included. For each participant, three regions of interest (ROI) with ICDAS codes 0, 1 or 2 were defined. All ROIs (n = 117) were investigated/imaged with laser fluorescence (LF, DIAGNOdent 2095; KaVo dental GmbH), quantitative light-induced fluorescence (QLF; Biluminator 2+, Inspektor Research Systems B.V.) and spectral-domain optical coherence tomography (SD-OCT; Telesto II, Thorlabs GmbH). The values of LF, ΔF of QLF, and the lesion extent assessed by OCT were categorized. Frequency distribution of LF-/QLF- and OCT-scores was determined for each ICDAS code included. Inter- and intra-examiner reproducibility of QLF and OCT measurements were assessed by unweighted kappa coefficient (ĸ) and Wilcoxon test (α = 0.05). Compared with LF and QLF, OCT showed various manifestations of carious lesions for visually sound ROIs and a larger variation of caries extent in depth within the same ICDAS code groups. Intra-examiner reproducibility ranged between 0.49 and 1.00 for the QLF analysis and between 0.95 and 0.99 for the OCT analysis. Inter-examiner reproducibility ranged between 0.17 and 0.32 for the QLF analysis and between 0.65 and 0.79 for the OCT analysis. LF and QLF were insensitive to less pronounced smooth-surface lesions while OCT allowed differentiation based on the penetration depth of the carious lesions. This makes OCT a suitable method to complement conventional visual inspection in order to detect and assess (very) early lesions.