No. Fluorides, such as those used in community water, toothpaste, gels, varnish, and mouthrinse also help to prevent decay. Fluoride works best on the smooth surfaces of teeth. The chewing surfaces on the back teeth, however, have tiny grooves where decay often begins. Sealants keep cavity-causing bacteria out of the grooves by covering them with a safe plastic coating. Sealants and fluorides work together to prevent tooth decay.