R.J.
My husband's family is like this. ALL the kids on his side of the family essentially have to have their baby teeth pulled as they come in. If not, within 6 months they have massive systemic infections from abscesses (they used to have a really high rate of infant mortality... more than half the babies in his family tree died by 18mo). My neice and nephew got off the "lightest" in that side of the family. The only had to have about half their teeth pulled, and the other half they got caps on.
Looks like my BILs genetics "helped" with some of the dentin production. They all have fairly healthy adult teeth, but are very prone to cavities. They all have *excellent* oral hygeine. It's just bad genes.