This study investigated the utility of using OCT to monitor SDF application over time. Twenty dentin blocks each with 5 windows were exposed to a demineralization solution to produce carious lesions. Treatment windows included sound, sound+SDF, lesion, lesion+SDF, lesion+SDF+SDF. Lesion depth, mean reflectivity over the lesion depth and optical penetration through the lesions were monitored with OCT for 12 weeks. OCT was able to show changes in the reflectivity and optical penetration in demineralized and sound dentin after SDF application over time. Such changes can potentially be monitored to determine if and when re-application of SDF is needed.