That’s Denture-Tainment
This Reddit member took her daughter to the beach to look for shark teeth and made a finding that will make your teeth clatter and is, well, pretty awful. She certainly wasn’t expecting to hear her daughter exclaim, “I found teeth!”
Perhaps Grandpa brought them to the beach and abandoned them there. Maybe a ship carrying artificial teeth sank and the cargo was dispersed?! Sand between the teeth is a creepy thought either way.