Parents, want to make your child’s mouth basically cavity-proof? Have them get dental sealants. That’s the latest message from the American Dental Association.

So, what exactly is a dental sealant? It’s a clear liquid gel that a dentist applies to the chewing surfaces of the back teeth that keep germs and food particles out. And it’s those back teeth where the most tooth decay tends to happen, because it’s harder to thoroughly clean them. Experts say that sealants are incredibly effective, studies show that dental sealants reduce cavities by 80-percent for about a decade.

But a new CDC study found that only 30-percent of children that need sealants get them. Which means their odds of developing a mouthful of costly and painful cavities spikes.

So, why aren’t kids getting the sealants they need? Experts say it’s because a lot of dentists didn’t learn how to apply sealants in dental school, so they flat out don’t offer that treatment, even though it’s relatively simple compared to other dental procedures, like a root canal.

But before you rush to the dentist demanding they seal your child’s teeth, keep in mind that not all children need them. If your kid is a master brusher and flosser, they should be okay sealant-free. But only a dentist can determine that, so ask if your child needs it at their next appointment.