This isn't necessarily true right, but it's a good place to start.

When I was shopping around for new dental insurance, none of the ones on the Marketplace showed my dentist. I made a short list and called my dentist and asked if they covered any of them. For some, the receptionist wasn't even sure if they took them, which was frustrating. She flat-out said "sometimes we won't know until we run the card" which was annoying. At any rate, found one from the Exchange she recognized/knew they took, and that was that.

I've intentionally avoided health insurance that's bundled with dental (even though it's a bit more cost effective,) because I like my dentist and would rather stick with them.