> I have a dental hygienist friend who told me many people take their hypnotherapist with them to the dentist to calm them and that it works.
Much more common, though, is for people to receive hypnotherapy to remove their anxiousness about dentistry without the need for their hypnotherapist to go with them. Typically, this will involve implanting the suggestion into the patient's brain that going to the dentist is not an unpleasant experience and that there's really nothing to fear. This will be triggered either when the patient walks into the dentist's premises or by recitation of some sort of trigger phrase. Deep down, the patient knows that visiting the dentist is beneficial to health and, with very few exceptions these days, completely pain-free, so there is very little "leap of faith" required to remove the anxiety.
This is also why hypnotherapy for quitting smoking (which I had) has such a high success rate. Everybody knows that smoking is a health hazard so, by extension, stopping smoking is beneficial. Also, if you've made the conscious decision to visit a hypnotherapist you clearly WANT to stop smoking anyway...