A root dentin single-section model was developed to compare the efficacy of different fluoride treatments on the remineralization of lesions. Shallow (∼170 μm) and deep (∼400 μm) lesions were produced in acetic acid buffer solutions (pH 5.0) with 0.1- and 0.5-ppm fluoride for 3 days and 2 weeks, respectively. Next, the sections were pH-cycled for 4 weeks. Following the pH cycling, all sections were first remineralized for 5 weeks, then subjected to 10 days of demineralization. The treatments were (1) no treatment (control), (2) daily 1,450-ppm NaF toothpaste, (3) weekly 4,000-ppm fluoride solution, (4) a combination of treatments 2 and 3. In the shallow lesions, the 4,000-ppm fluoride solution and the combination treatment enhanced mineral deposition at the lesion front, producing a second, slightly hyperremineralized layer. Similarly, in the deep lesions a second remineralized layer was detected. In all lesions, the fluoride solution treatment showed significantly more remineralization compared to the control and the toothpaste treatment (p<0.05), most of which was formed during the pH cycling. In the demineralization period, the control showed significantly higher mineral loss than all other treatments. These results indicate that a 4,000-ppm fluoride solution might be effective for remineralization of root dentin lesions even over 400 μm depth.