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.
Don't stress - enjoy!