This study evaluated the artificial caries resistance provided to white spot lesions by sealing with an unfilled resin. Twenty extracted molar teeth were coated with an acid-resistant varnish (ARV), except for two 5 mm x 2 mm enamel windows (mesial and distal), and immersed for 5 weeks in an acidified gel brought to a pH of 4.2 with lactic acid. White spot lesions (not frank caries) were created in each window. The teeth were removed from the gel, rinsed and dried. One window was divided into two equal parts; one half was covered with the ARV (Group 1); the other half was not covered (Group 2). The other window was treated with 37% phosphoric acid for 20 sec, rinsed with water for 20 sec, dried and sealed with Prisma Universal Bond 2 Adhesive (Group 3). The teeth were reimmersed in the acidified gel for 40 days until frank caries was induced in Group 2. Specimens were then removed from the gel, rinsed, and sectioned occlusogingivally. Sections were polished to approximately 100 microns, imbibed in water, and analyzed using polarized light microscopy. Depth of demineralization was evaluated in the varnished, sealed and frankly carious areas. The mean (SD) lesion depths were as follows: Group 1 (under ARV) 366 microns (103 microns); Group 2 (frank caries) 746 microns (219 microns); Group 3 (under sealed area) 298 microns (111 microns). ANOVA and Student-Newman-Keuls procedure were used to compare group means. The mean depths of demineralization under the ARV (Group 1) and the unfilled resin sealant (Group 2) were significantly less than for the unprotected enamel (Group 2) (p > 0.0001). Results indicate the potential effectiveness of sealing white spot lesions with an unfilled resin to prevent further demineralization.