The public health importance of root surface caries has increased due to increased longevity of life and retention of teeth. The restoration of root surface caries continues to be problematic, with few published clinical studies and few guidelines having been established. Although topical fluorides are clearly effective in the control of coronal caries, their efficacy in the management of root caries has not yet been well elucidated. Few clinical studies have investigated the use of topical fluorides in the prevention and treatment of root caries. No randomized clinical trials have been reported on the treatment of incipient root caries with topical fluoride vs. placebo. The purpose of this study is to develop and pilot the methodology to be used in a subsequent, larger, randomized, clinical trial to evaluate the efficacy of 0.05% NaF mouthrinse in the arresting and reversal of incipient root caries lesions. Aspects to be piloted include the methodologies for lesion classification and measurement of lesion dimensions. Billings' Root Caries Severity Index will be used and reliability assessed. The height, width and area of incipient lesions will be measured clinically. Lesions will be photographed with a standard circle coronal to the lesion. The area of the lesion will then be calculated from the photograph using a digitizer after normalizing using the standard circle of premeasured area. Estimates of the efficacy of the fluoride mouthrinse will be essential for the calculation of sample size and power in the subsequent larger study. Forty individuals with incipient root caries will be randomly assigned to two treatment groups: 0.05% NaF mouthrinse and placebo mouthrinse. Subjects will be recalled at 3, 6, and 9 months and evaluated blindly. The findings will be invaluable in the planning of the subsequent larger clinical trial which will permit NaF mouthrinse to be recommended or not recommended for root caries reversal based on scientific evidence. If effective, these agents will greatly reduce the need for invasive, and often unsuccessful, restoration of root surface caries.