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Diffuse Reflectance Spectroscopy for Caries Detection and Discrimination of Restorative Materials: An In Vitro
Introduction:
Diffuse reflectance spectroscopy (DRS) is a proposed optical adjunct for caries detection, but its diagnostic accuracy against histology has not been validated alongside its ability to discriminate restorative materials. We aimed to validate DRS in vitro for both tasks.
Methods:
This in vitro study comprised two arms. In Part 1, 200 occlusal regions of interest from 100 extracted teeth were assessed by DRS (350-1730 nm) and by two independent examiners using the International Caries Detection and Assessment System (ICDAS), with histological scoring as the reference standard. In Part 2, four freshly prepared restorative materials (45 sites each: a self-adhesive resin cement, two resin composites, a resin-modified glass-ionomer) were compared with 37 sound-enamel sites from a separate cohort (one site per tooth). Spectra were classified by partial least squares discriminant analysis (PLS-DA) with specimen-grouped 10-fold cross-validation (sites from a specimen kept in one fold, preventing leakage).
Results:
DRS reached 80.5% exact agreement with histology (quadratically weighted κ = 0.916, 95% CI 0.890-0.939) versus 54.0-57.5% for the visual examiners. At the any-caries threshold (histological score ≥ D1), DRS achieved sensitivity 90.8% (95% CI 84.3-94.8) and specificity 95.0% (87.8-98.0), with four false-positive classifications of sound surfaces against 25 and 23 for ICDAS examiners. The DRS AUC (0.946) exceeded both examiners (0.908 and 0.914), reaching significance against one (DeLong test, p = 0.027). Sensitivity for dentin-level caries was low (37.5%). PLS-DA discriminated the five classes (four materials plus sound enamel) with overall accuracy 99.5% (95% CI 97.4-99.9).
Conclusion:
In vitro, DRS showed markedly higher specificity than visual ICDAS scoring for occlusal caries and discriminated four freshly prepared restorative materials from sound enamel. Its low sensitivity for dentin-level lesions and the controlled laboratory conditions warrant cautious interpretation pending in vivo validation.
