AbstractThe present study compares visible‐light Delton with Duraphat fluoride varnish for the prevention of occlusal caries in permanent first molars. A clinical trial was carried out in three groups of 6–8‐yr‐old schoolchildren: a sealant group (100 children), in which Delton light‐polymerized fissure sealant was applied to permanent first molars; a varnish group (98 children), in which Duraphat was applied to permanent first molars; and a control group (116 children). Replacement (sealant) and reapplication (varnish) was carried out every 6 months. Percent effectiveness at 24 months (percentage of saving from caries taking molars as analysis unit) for those molars initially healthy and with complete occlusal eruption was analyzed. 272, 252 and 238 molars met the inclusion criteria in the control, varnish and sealant groups, respectively. Of these, 45.2%, 28.2% and 10.5% developed caries after 24 months. The effectiveness was greater in the sealed molars than in the varnished molars