Tooth enamel laser irradiated under certain conditions previously has been shown to have reduced subsurface demineralization rates. Identification of these laser-induced changes has bearing on understanding the dissolution rate reduction mechanism; some of these changes, ones that occur in high temperature regions, were studied in this report. X-ray diffraction and infrared spectroscopy were used to identify changes in enamel of extracted intact human teeth subjected to high energy density (∼10,000 J/cm) 10.6 µm wavelength carbon dioxide laser irradiance. The laser irradiance melted the enamel apatite; this solidified melt was composed of minor phases of α-tricalcium phosphate, α-Ca(PO), and tetracalcium phosphate, Ca(PO)O, and a major phase of modified apatite. The apatite modifications, as compared with the original were (1) reductions in contents of water, protein, carbonate, and chloride (or chloride rearrangement); (2) essentially no change in apatite hydroxide content; (3) possible incorporation of oxide replacing some hydroxide ions; and (4) an uptake of traces of carbon dioxide and cyanate. An infrared band at 434 cm that appears in spectra of hydroxyapatite partially dehydroxylated by thermal treatment was assigned to oxide translation. This band was utilized to search for oxide formation in the laser-irradiated tooth enamel. [ABSTRACT FROM AUTHOR]