I just got home 10 minutes ago from having my teeth cleaned, and the procedure, with full x-rays and a very quick check-up by the dentist took one hour (I'm in Southern California). If the hygienist had started talking about something I wasn't interested in hearing, either politics or how fabulous his kids were at underwater basketball, or really anything at all, I would have stopped the monologue right away and asked for quiet, please. It's tough enough being poked and prodded and keeping my mouth open for an hour without having to endure small talk that I don't appreciate. Even with a late start and your estimate that you spent the first 10 minutes replying, that is still half an hour longer than necessary and I agree with PP that I'd complain to the dentist and be clear that I didn't want that hygienist ever again.
You're the customer, you're paying for a service, and you shouldn't have to put up with unwelcome comments or similar 1-sided conversations you don't want to hear when you're a captive audience. That goes for when you're getting a massage, a haircut or nail appointment, or anything else. Just speak up as soon as you're bothered. You could say something like, "Please change the topic to something more relaxing instead of politics (or whatever), or it's fine with me if we don't converse at all as I'm trying to de-stress."