I think the parent comment was referencing that, at least in the US, dentistry is treated differently in many ways. For example, it’s a different health insurance with its separe premiums and limits, and you’ll never find a dentist in a hospital; instead they have their own offices.

In the US, dentistry isn't a specialization of medicine. Medical specializations have to go to medical school then residency first before specializing. Dentists just go to dental school. Dentists in the US aren't medical doctors any more than JDs or PhDs are.