Investigation of in vitro dental erosion by optical techniques

Nitrogen laser-induced fluorescence (LIF) and tungsten halogen lamp excited diffuse reflectance spectra were recorded in 350- to 700-nm range on a miniature fiber-optic spectrometer from in vitro premolar tooth during various stages of artificial erosion with 36% phosphoric acid. Both the LIF spectral intensity and the diffuse reflectance intensity gradually increased during tooth erosion. The LIF spectra were analyzed by curve fitting using Gaussian spectral functions to determine the true contribution of different bands in the spectra during erosion. Thus, the broad bands at 440 and 490 nm in the LIF spectra of sound enamel were resolved into four peaks centered at 409.1, 438.1, 492.4 and 523.1 nm and of sound dentin into peaks at 412.0, 440.1, 487.8 and 523.4 nm. The F410/F525 ratios derived from curve-fitted Gaussian peak amplitudes and curve areas were found to be more sensitive to erosion as compared to the diffuse reflectance ratio R500/R700 or the raw LIF spectral ratio F440/F490.