Mechanism of laser-induced solubility reduction of dental enamel

Several studies in our laboratories have demonstrated that CO2 laser treatment of dental enamel can inhibit subsequent caries-like progression from 10-75 percent compared to controls. The present study tested the hypothesis that laser radiation at specific wavelengths is absorbed by the mineral, converted efficiently to heat at the surface, causing thermal decomposition of the carbonated apatite enamel crystals to a less soluble form. Samples of enamel 5 X 5 mm were examined before and after laser irradiation by specular reflectance FTIR. Sample surfaces were irradiated by pulsed CO2 laser at 9.3, 9.6, 10.3 or 10.6 micrometers , 100 microsecond(s) pulse duration, 25 pulses per spot, with fluences of 0-6 J/cm2. In separate experiments surface temperatures were measured dependent, and fluence dependent, with total loss occurring with 9.6 micrometers irradiation occurred at 4 J/cm2. Optimum inhibition of caries progression following 9.6 micrometers irradiation occurred at 4 J/cm2. We conclude that irradiation of dental enamel by specific wavelengths and fluences of CO2 laser light alters the chemical composition of the crystals, decomposing the CO3 component, thereby markedly reducing the reactivity.