Teeth, dental bridges, fillings, etc... like this , that are found on beaches, are coming from people who scatter their loved one's ashes in the surf .
My dad did a lot of volunteer work , at his church, assisting in funerals (pallbearer, receptions, usher, etc...). And it was not uncommon for the details, in the will, to stipulate "scattered at sea".
And a lot of times, they would just take the ashes to the beach , and scatter them in the surf. Another way is you can hire a private pilot, who offers the service of flying them out over the ocean, to deeper waters. But that costs $$ , and the pilot will wait till he's got multiple baggies waiting to go, etc...
The entire remains of a human body, after cremation, fits into a small baggie, that can fit in the palms of your hands. And dental metal will survive the cremation (albeit often distorted and semi-melted).
The reason I suspect that this is where the teeth on beaches comes from, is also because it's not uncommon for us md'rs to find "toe tags" on the beach. That would be the little dog-tag type thing that's added in , to the ashes, after the cremation I guess.