Abstract: Several studies in our laboratories have demonstrated that CO$- 2$/ laser treatment of dental enamel can inhibit subsequent caries-like progression from 10 - 85% compared to controls. The reasons for these observed effects are still unclear. The aim of the present study was to combine and interpret results from in vitro caries experiments, single and multiple pulse temperature measurements, SEM observations, and crystallographic measurements, each following CO$-2$/ laser irradiation of dental enamel or synthetic carbonated apatite. Optimum caries inhibition in enamel appears to be achieved by pretreatments that produce surface temperatures in the range of 600 - 1000$DGR@C. For clinical application the surface enamel heating must not lead to consequent pulp chamber temperature rises of $GRT 4 $DGR@C. To meet these conditions a pulsed laser with a sufficiently high absorption coefficient ($lambda $EQ 9.3 or 9.6 $mu@m), pulse width near the thermal relaxation time of enamel (50 - 100 $mu@s), minimum useful number of pulses (approximately 25), low repetition rate (approximately 10 Hz), and low but effective fluence (approximately 1-5 J/cm$+2$//pulse), works well. !30
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