A confocal microscopic study relating the autofluorescence of carious dentine to its microhardness

Objective An in-vitro study to examine the correlation between the distribu tion of the autofluorescent signal emitted from carious dentine (detected u sing confocal laser scanning microscopy) and its microhardness, within the depths of human dentine lesions. Materials and methods Twelve carious teeth were sectioned longitudinally, t he cut faces marked with a grid reference line system and colour photomicro graphs taken. The same samples were imaged using confocal laser-scanning mi croscopy for autofluorescence and then subjected to microhardness testing u sing a Knoop microhardness indenter. Adjacent sound dentine was used as a c ontrol reference. Digital image superimposition allowed direct comparisons to be made between the colour, autofluorescence and microhardness of each l esion. Results Sound enamel and dentine did not autofluoresce. Autofluorescence di stribution from carious dentine correlated with the highly softened tissue (detected using the Knoop indenter) and terminated at a level superficial t o the translucent zone. This zone was still pigmented. Normal, sound dentin e hardness levels were found deep to the translucent zone. Conclusions A correlation existed between the zone of autofluorescence and carious dentine that was markedly softened by the carious process. These fi ndings highlighted a possibility that the autofluorescence might be used as an in-vitro, objective histological marker for the softened, carious denti ne requiring clinical excavation.