omg yes! The dentist's going to stick their face right in his! after having stuck their face right into a bunch of other patients! and then they'll stick their face into a few more patients! It sounds like the perfect breeding ground. Even if I wasn't sick, I'd want to cancel for that alone!

Yeah but they use protections like masks, gloves. I think it's reasonable to assume that a dentist's office likely know better than you about how to minimize the risk. They have motivation in not ruining their business by being a source of local outbreak.