Tooth stuff, the "realm of the mouth" as it were, is where Gabriel's most primal horrors are situated. I don't have the particular problems he has, and has endeavored to resolve by resorting to the predations of unaccountable forest mystics. But that's only an index of how much he loathes Dentists as a profession.
I did have braces, as he does now, and I found it pretty fucking unpleasant. It wasn't as bad for my daughter, or maybe her chompers were just less fucked up, because the whole run was like a year. I had these things for four years, long enough for the feel of my regular human teeth to be completely disgusting. I can still feel them popping the caps off to remove them, and the wirecutters between the teeth.
I can also remember opening my locker at Dr. Jonas E. Salk Middle School not because I needed a book - I liked to carry them all in my backpack - but I so I could hide my face in the locker and cry there. This had to be the least convincing maneuver of all time, and then you just hauled your wet scrunchy face out of it and everybody knew anyway. All I can suggest in my defense is that the immediacy, urgency, and depth of this kind of pain confounds the mind; My wish for him is less pain, on an accelerated timeline.