The gradient of structural alteration and molecular exchange across CO(2) laser-irradiated areas in dental enamel was analyzed by Raman and attenuated total reflectance infrared microspectroscopy. The type and the degree of structural changes in morphologically distinguishable zones within the laser spot vary depending on the laser-irradiation parameters--power (1 and 3 W), treatment time (5 and 10 s), and operational mode (super pulse and continuous wave). Using higher power, irrespective of the operation mode, the enamel tissue ablates and a crater is formed. The prevalent phase at the bottom of the crater is dehydrated O(2) (2-)-bearing apatite, that is, the fundamental framework topology is preserved. Additional nonapatite calcium phosphate phases are located mainly at the slope of the laser crater. No structural transformation of mineral component was detected aside the crater rim, only a CO(3)-CO(2) exchange, which decays with the radial distance. A lower-power laser irradiation slightly roughens the enamel surface and the structural modification of enamel apatite is considerably weaker for continuous wave than for super pulse mode. Prolonged low-power laser treatment results in recrystallization, and thus structural recovering of apatite might be of clinical relevance for enamel surface treatments.
