Below the threshold for
laser ablation, the
mineral phase of enamel is converted into a purer phase
hydroxyapatite with increased
acid resistance. Studies suggest the possibility of achieving the conversion without visible surface alteration. In this study, changes in the surface morphology, reflectivity, and
acid resistance were monitored with varying irradiation intensity. Bovine enamel specimens were irradiated using a CO 2
laser operating at 9.4 ?? ? m with a Gaussian spatial beam profile—1.6 to 3.1 mm in diameter. After
laser treatment, samples were subjected to demineralization to simulate the acidic intraoral conditions of
dental decay. The resulting demineralization and erosion were assessed using polarization-sensitive optical coherence tomography, three-dimensional digital microscopy, and polarized light microscopy. Distinct changes in the surface morphology and the degree of inhibition were found within the
laser-treated area in accordance with the
laser intensity profile. Subtle visual changes were noted below the melting point for enamel that appear to correspond to thresholds for denaturation of the organic phase and thermal decomposition of the
mineral phase. There was significant protection from
laser irradiation in areas in which the reflectivity was not increased significantly, suggesting that aesthetically sensitive areas of the tooth can be treated for caries prevention.