Why don't you teach him to drop his head? With a horse of that size, I feel that is pretty much a necessity for anything (haltering, bridling, trimming a bridle path, brushing the mane, etc). Do you know how to teach a horse to drop its head? If not, I can post details.
You *may* need to have his teeth checked again. Some horses need it done every 6 months; others only need it once a year.
What happens when you take the bridle OFF? Does the bit bang on his teeth as its coming out? Be very careful that it doesn't.
With both bridling and unbridling, be very careful you aren't bending his ears in weird ways or anything like that.
Anything that YOU do when bridling or unbridling that causes pain or discomfort (ex: bit hitting teeth on the way out) can cause him to not want to put that bit back in his mouth again. So just be careful of your actions too.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.