New2This: Just returned from Holland America's Maasdam for 2 weeks and had occasion to visit the infimary for the headcold from hell (probably from the plane). There was a sign that said, "Dentist available by appointment", with a phone number.
On a Princess cruise a few years ago, a friend lost a filling at dinner and told the head waiter. Within minutes, a dentist appeared at our table and made arrangement for an appointment the next morning. Didn't appear as if he was employed as a permanent part of the staff, but perhaps a vacationing dentist who made arrangements with the line to be on duty in exchange for a free cruise - not sure how it worked, but he fixed up my friend in a jiffy. The equipment was adequate, probably not state of the art, but it worked.
With between 700 and 1,000 crew members with long contracts, there must be someone on board at all times to deal with dental problems.
I think there are because my dentist told me that he was offered a job on a cruise ship. He turned it down because he found out that a dental plan is part of the crew's benefits, and a majority of his time would have been spent working on the crew's teeth..
My family and I went on the Radiance a few months ago and my mom got a horrible toothache and they did not have a dentist on board. The regular doc told my mom to go see a dentist at the next port. Just a word of advice I would only go to the doctor on board only if you have an extreme emergency, because it costs us $250 for 8 pain pills.