Dentist: Molly, do you know what a dental dam is?
Molly: Yes.
Dentist: Have you ever used one?
Molly: Er, yes?
Dentist: Well, we’re going to be using something slightly different. It’s a lot better because it provides more suction, and it’s got this area where you can rest your jaw.

The other device was indeed much nicer to have stuffed in my mouth for two hours than a dental dam would have been.