How many companies of any type hire in-house dentists? Precious few, I suspect, even when they have thousands of people in a single complex. Now factor in how airline employees are based at airports all over the place, and often travel for work. It might be an interesting fringe benefit - "get your x-rays while you overnight at DFW, then get the cavity filled on your next trip!" - but I'd say the chances of that, in today's economic climate, are pretty small.

Also, they can't just hire a dentist. They'd have to allocate space for and equip a dental office, hire one or two hygienists, set up a procedure for booking appointments, put someone in charge of doing that ... It becomes a major investment. It also could, in theory, expose them to a new kind of liability. As a minimum, they'd have to take out some form of malpractice insurance.

Bottom line is that an airline would probably hire a dentist only if he/she were willing to train for a new career as a flight attendant, desk agent or baggage handler (or just happened to have a commercial pilot's license with a multi-engine rating and a few thousand flight hours). These are, unfortunately, exactly the same circumstances under which they'd hire anyone else.