@Dreamnghrt: Societal holdover from when dentists were considered to be (and not infrequently were) quacks long ago, as in the Old West and up around the turn of the previous century. Also, dental insurance is a mint-maker (no pun intended), and so some of the lesser-known but hugely profitable dental/specialty-only insurers don't want dental to be primary. Others don't want it to either because dental problems are as common as the cold, which they like not because premiums would have to be...
@Dreamnghrt: ...higher and not for profit-making or dividends but for payouts. Also, there's likely be even more stringent regulation, *and* at least half of Congress and one entire political party don't want dentistry or orthodontics included in Medicare. It would truly be phenomenally expensive when you consider its primary demographic. Medicaid covers dental, however, and nearly always has, if I recall rightly.