That's pretty awesome for some folks - my uncle had three sets of teeth, so the last set was extremely brittle. I'm curious if calcium supplements and this drug could provide an alternative to dentures.
No, some people have a complete third set. Some people only have a partial third set, or even have third teeth in just a few positions within the mouth. A dentist who told me about this said it's a little rare, but not super rare.
Yes, they came in in his thirties, which was like 40-50 years ago. It hasn't happened to anyone else in the family thankfully, though he himself never had kids.