| Many studies proved the caries preventive effect of laser irradiation on enamel surfaces. Laser types investigated include: Nd:YAG, argon, and CO2, used alone or together with topical fluoride application. However, certain issues still need to be investigated such as comparing these laser types to determine the most effective system, and the best sequence of topical fluoride application (APF): before or after laser irradiation. The purpose of this study was to compare the effects of three commercial laser types (Nd:YAG, argon, and CO2) used alone or with APF on sound (phase 1) and demineralized (phase 2) enamel surfaces. In phase 1, 132 human molars were ground on axial surfaces to prepare 3 x 3 mm enamel windows which were divided into 11 treatment groups: each laser alone, each laser with APF gel (before or after irradiation), a positive control (APF), and a negative control (no treatment). After treatment, specimens were demineralized for 96 hours in a lactic acid/carbopol solution at 37°C. In phase 2, 3 x 4 mm enamel windows were prepared on 120 human molars, as in phase 1, after grinding enamel surfaces. Specimens were demineralized for 96 hours. One third of the window was covered with acid resistant varnish and served as a baseline lesion, and the remaining exposed window received different treatments: each laser alone, each laser with APF gel (before or after irradiation), or APF as a positive control group. Half of the treated window was then covered by acid-resistant varnish, and the remaining half was further demineralized for 96 hours. Fluoride biopsies were performed in both phases to determine fluoride levels in specimens. Specimens were sectioned and analyzed for lesion severity using confocal laser scanning microscopy. All three lasers tested alone or combined with APF, significantly enhanced enamel resistance to chemical dissolution. In phase 1, laser fluoride combination totally prevented lesion development. In phase 2, laser fluoride combination prevented further demineralization of incipient lesions. However, the use of Nd:YAG laser for caries prevention should not be recommended since it undermined the tooth structure by producing numerous fissures, cavities and areas of enamel exfoliation as seen by scanning electron microscopy. |
