I went through this about 3 months ago. It had to be done in 2 visits because they won't numb the whole of your mouth up so obviously do one side each visit. It's about 4-5 injections upper then same again lower, when they injected the front the first time it felt like the needle was going through my nose....certainly makes the eyes water. 2nd visit she put numbing cream on a pad and placed it behind upper lip for a few minutes, didn't feel the needle that time so ask if you can have that done prior to injection. Once numbed, the deep clean wasn't a problem, never felt any pain.
Hope that helps :)
Hope that helps :)