Wavelength-Dependent Fibre-Optic Transillumination of Small Approximal Caries Lesions: The Use of a Dye, and a Comparison to Bitewing Radiography

The mere detection of caries lesions is insufficient for optimal treatment decision-making. Hence, the aim of this study was to investigate whether quantitative information about approximal lesion depth can be obtained from a technique based on the wavelength dependency of light propagation and additional use of a dye. Another aim was to compare the diagnostic performance of the optical technique and bitewing radiography. Measurements were performed on 33 extracted premolar teeth. Twelve proximal surfaces had white-spot, and 17 had discoloured small lesions. Four surfaces were sound. The teeth were transilluminated with a single glass fibre at the approximal surface before and after dye application. The occlusal surface was imaged with a CCD camera. Light in the blue and red part of the electromagnetic spectrum was selected using Schott glass filters. Average decadic optical thickness differences, delta bl-rd tau eff, were estimated and plotted as a function of normalised lesion depth, dhist, established from histological validation by two observers. The Spearman rank correlation was rs (delta bl-rd tau eff, dhist) = 0.87 (95% confidence interval, CI: 0.74-0.94). A marked increase in average decadic optical thickness in the blue part of the electromagnetic spectrum, delta dye tau eff, was observed for those lesion that, upon direct visual inspection of the approximal surface, clearly showed dye uptake. Bitewing radiographic depth ratings of two observers were plotted as a function of dhist. The correlations were rs (dRA,1, dhist) = 0.62 (95% CI: 0.34-0.80), rs (dRA,2, dhist) = 0.75 (95% CI: 0.54-0.87), and between the observers rs (dRA,1, dRA,2) = 0.44 (95% CI: 0.10-0.69). The p values of rs (delta bl-rd tau eff, dhist) -rs (dRA1,1, dhist) and rs (delta bl-rd tau eff, dhist) -rs (dRA,2, dhist) were p1 = 0.01 and p2 = 0.08, respectively. It was concluded that quantitative information about lesion depth can be obtained optically. The dye penetrates into only a limited number of caries lesions, in which cases dye uptake is detectable in transillumination geometry. Under laboratory circumstances the optical technique performs as well as bitewing radiography in the diagnosis of small approximal caries lesions.