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Effect of pulse duration and repetition rate on CO2 laser inhibition of caries progression

Several studies in our laboratories have demonstrated that CO2 laser treatment of dental enamel can inhibit subsequent caries-like progression from 10 - 85% compared to controls. The roles of several of the laser parameters in the observed inhibition are still unknown. The aim of the present study was to examine the roles of pulse duration and repetition rate by the use of in vitro caries experiments, single and multiple pulse temperature measurements, and SEM observations, each following CO2 laser irradiation of dental enamel. We used pulse durations of 100 and 500 microsecond(s) at wavelengths of 9.3, 9.6, 10.3 and 10.6 micrometers , fluences of 2.5 or 5 J/cm2 per pulse, and 25 pulses per treatment window on human enamel. To study repetition rate we used 26 pulses, wavelength of 9.3 micrometers , at 1, 10, 25 or 40 Hz, with a fluence of 2.5 or 3.5 J/cm2 per pulse. A complex relationship among pulse duration, wavelength and fluence was demonstrated. Increasing the repetition rate improved the inhibition up to a plateau at 25 Hz. Optimum caries inhibition in enamel appears to be achieved by pretreatments that produce surface temperatures in the range of 800 - 1000 degree(s)C. Optimization of pulse duration, wavelength and repetition rate should allow for effective clinical caries inhibition with short treatment times and minimal change to surface topography of enamel.