Sealants can dramatically reduce the number of cavities a child might develop throughout their childhood. On the chewing surface of molars, deep grooves run into the center of the teeth. Under a microscope, these crevices might look like a deep canyon. In reality, most of them are narrower than a single toothbrush bristle but that is still wide enough for bacteria to hide. If the grooves in permanent molars are sealed at a young age, the risk of decay decreases dramatically.