摘要： Objective: This study aimed to assess the efficacy of erbium?doped yttrium aluminum garnet (Er:YAG) laser, pastes containing casein phosphopeptide amorphous calcium phosphate (CPP?ACP) with and without fluoride and their combination for prevention of white spot lesions in the enamel. Materials and Methods: This in vitro experimental study was conducted on 90 extracted sound premolars. The teeth were then randomly divided into six groups of 15: (1) Control, (2) laser, (3) CPP?ACP with fluoride (GC MI Paste, Recaldent? 900 ppm as NaF), (4) CPP?ACP without fluoride (GC Tooth Mousse Recaldent?), (5) laser + CPP?ACP with fluoride, and (6) laser + CPP?ACP without fluoride. In each group, enamel surface was exposed to the remineralizing agent. The teeth were then subjected to pH cycling for 14 days. The teeth were then sectioned, polished, and underwent cross?sectional microhardness testing at 20–160 μ depth quantitatively. Using the Simpson’s rule, the amount of mineral loss was calculated in each group. Statistical Analysis Used: ANOVA was used for the comparisons, and Tukey’s test was applied for pairwise comparisons. Results: The highest mean volume percentage of microhardness at 20–60 μ depth belonged to the group laser + CPP?ACP with fluoride and the lowest belonged to the control group (P = 0.001). The differences were not significant at 80?120 μ depth (P > 0.05). These finding are confirmed according to ?Z (mineral loss). Conclusion: Based on these results, Er: YAG laser was able to decrease demineralization and was a potential alternative to preventive dentistry and was more effective when combined with CPP?ACP products.