In this 4-year follow-up in vivo controlled study, 112 human permanent first molars from children between 6 and 11 years old were used to investigate the viability of the carbon dioxide (CO2) laser in promoting caries-free occlusal surfaces in permanent molars as an isolated form of treatment or associated with conventional fissure sealants. The findings suggest that occlusal caries prevention only by means of CO2 laser irradiation is not effective; that the utilization of photoactivated sealants, as well as its association with CO2 laser, applied over the occlusal fissures, are effective means of preventing occlusal caries, and that the application of CO2 laser over occlusal fissures prior to the application of a photoactivated fissure sealant improves the retention of the sealant.