The objectives of this study were first, to compare the effects of CPP-ACP fluoride varnish and CO2 laser in preventing enamel demineralization, then to determine for how long the varnish prevents enamel demineralization, and finally to determine how often should it be reapplied to maintain the preventive effect. Human molars and premolars were halved. First experiment, teeth sections were randomly assigned to fluoride, laser, or control group. After pH-cycling enamel demineralization and mechanical properties were evaluated using the FluoreCam and CSMH, respectively. For the second experiment, teeth sections were randomly assigned to either fluoride or control groups, varnish was applied to one group, the specimens were placed in a tooth-brushing simulator, thermocycled, and subjected to pH cycling. Using the same procedures the third experiment compared one fluoride application, to multiple applications, either every 4 or 6-weeks. In the first experiment, the FluoreCam results significantly greater effects in the fluoride group than in the control and laser groups. Enamel microhardness was significantly greater in the fluoride than laser group, which was in turn harder than the control group. The second experiment showed significant and progressive demineralization in the control group at 2, 4, 8, and 12 weeks (p<0.001). The experimental group revealed no demineralization during the first 4 weeks and only limited demineralization after 12 weeks. PLM revealed typical WSLs in the control and more limited demineralization in the treated group. The third experiment showed significantly larger areas of demineralization in the control than the 6-week and 4-week groups. There were no statistically significant differences between 4- and 6-week groups. In conclusion, CPP-ACP fluoride varnish is more effective in preventing enamel demineralization than CO2 laser. It prevents demineralization completely for at least 4 weeks. Because the preventive effect starts to decline after 6 weeks, the varnish should be reapplied at least every 4 weeks.
