Dental "slide" film is certainly still made. Some dentists have converted to digital X-rays, but this is still very uncommon. Many dental specialists and doctors I have talked to have said they have no plans on converting. Dental film is not made in 35mm cassettes though. It is exposed in a light-tight cassette by an x-ray source. I'm not sure how you could adapt this to artistic imaging purposes. It is also made in sheets, I believe, but not for dental x-rays. You'd have to visit a local hospital and ask if you could buy a small quantity or have some of their old or left-over film.
Regards.
Karl Borowski