Many sports – especially high-contact sports such as football, basketball and wrestling – pose a serious risk for mouth injuries, from biting the lip or tongue to broken or chipped teeth.

Dentists strongly encourage athletes, from casual players to three-sport high school athletes, to use mouth guards, which protect their teeth and mouth. Unfortunately, a large majority of children – more than four of every five – participating in organized youth sports skip wearing a mouth guard, largely because many organizations don’t require them, according to the American Association of Orthodontists.

It’s a big mistake, and a huge risk. About 25 million children participate in competitive sports in the U.S., and many of those children suffer injuries on the court or field. About 15% of those injuries are to the mouth, according to the American Dental Association.

A bone-crushing tackle, a comebacker in baseball or softball, an elbow in the mouth while going up for a rebound. Each can turn a bright smile – and a happy day – into an unexpected, emergency trip to the dentist to fix a broken or knocked-out tooth.

And those athletes without a mouth guard have a greater chance, as much as six times more likely, of an injury to their mouth, according to the National Youth Sports Foundation. Another study, which only looked at contact sports, found athletes without mouth guards were twice as likely to suffer an injury to their mouths or teeth. Regardless, skipping a mouth guard is more likely to cost you.

But perhaps the biggest reason to use a mouthguard is when accidents happen, and they certainly will, the often-overlooked sports equipment can be a teeth-saver, according to Dental Traumatology. Mouth guard users were at least 80% less likely to suffer dental injuries compared to those without a mouth guard.

So, as you can see, a mouth guard should definitely be on an athlete’s must-have sports equipment shopping list, and in their mouth before the game starts.