Optical quantification of approximal caries in vitro.

A fluorescent dye was applied to extracted premolars with either early artificial lesions or natural white-spot lesions. The teeth were placed in an approximal geometry, and with a specially designed fibre-optic probe the fluorescence of the dye was measured in the lesions. The same fibre-optic probe was used to measure the transmission of light at a wavelength where the dye does not absorb. This transmission of light was used to correct the fluorescence for attenuation by the intermediate layer of sound enamel situated between the probe and the lesion. Both signals varied with time because of the necessary addition of ethanol during the measurement. The mineral loss from the lesions was measured with wavelength independent microradiography (WIM) for the artificial lesions, and the optical caries monitor (OCM) for the natural white-spot lesions. The correlation coefficient between corrected fluorescence and mineral loss was r = 0.86. The results indicate that measurement of dye uptake may be a very sensitive method to diagnose early approximal caries lesions and may enable quantification of these lesions.