A comparison of two histological validating techniques for occlusal caries

Validation of a diagnostic technique is important to establish whether it actually measures what it is purported to measure. However, the accuracy of the validation technique per se can influence the apparent accuracy of the diagnostic technique.

The aim of this study was to describe two alternative histological validating techniques for occlusal caries and to compare quantitative depth measurements of carious lesions taken using each method.

Thirty sections (mean thickness 0.67 mm) were cut to include two to four discrete sites in 10 freshly extracted teeth. The first histological validating technique used a microfocal X-ray unit to produce magnified high definition radiographic images of the sections or 'macroradiographs'. An image analysis system was used to make quantitative measurements of the lesions (if present) with respect to the enamel-dentine junction (EDJ). The second validating technique used a confocal microscope to image beneath the cut surface of the section. Quantitative measurements were taken from the fluorescence images of both sides of each section and a mean depth measurement calculated.

Complete agreement was found between the two validating techniques for the subjective interpretation of the presence and extent of caries. A strong positive relationship was found between the two histological validating techniques for depth measurements made of dentine caries from the EDJ (r = 0.93, P < 0.001). Depth measurements made from the macroradiographs were greater than from the confocal fluorescence images (mean difference = 0.41 mm).

Both validating techniques enable the identification of sound sites, those with enamel caries and dentine caries. However, quantitative assessments made with each technique could result in disagreement.