Multiple-pulse irradiation of dental hard tissues at CO 2 laser wavelengths

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Abstract
Surface temperatures were monitored using pulsed photothermal radiometry (PPTR) during multiple pulse carbon dioxide laser irradiation ((lambda) equals 9.3, 9.6, 10.3 and 10.6 micrometers ). Permanent changes in the optical properties (reflectance and absorption) were observed at fluences greater than 2 J/cm2 for dentin and 5 J/cm2 for enamel. The laser irradiation changes the thermal and the optical properties of these tissues, substantially changing the energy deposition for subsequent laser pulses. The temperature response of enamel and dentin and the reflectance of dentin changed considerably with successive laser pulses. After 10 to 50 pulses the surface stabilized and no further changes were noted. Scanning electron micrographs of the laser conditioned surfaces showed large crystals of modified hydroxyapatite (approximately equals 500 nm) devoid of the organic matrix. Presumably, the water and the interwoven biopolymer matrix had been carbonized nd vaporized. Caries inhibition measurements after multiple pulse irradiation of enamel indicate that the stable laser conditioned surface is more resistant to acid dissolution than untreated enamel.

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