Mouth rot: what do i look for?

I just tried to feed my BP Tu'. I thought he was hungry because this morning early he looked to be roaming and pacing the cage. So I opened the top and he came to my hand like normally and sat his head in my palm but he started hissing. He did this like three or four times in a row so I put him back inside! Then when i was trying to feed him I noticed he was missing a tooth in the front bottom left side. is it normal for them to lose teeth maybe from biting mice and getting them snagged or something and if they lose a tooth or two does that mean he will have problems with mouth rot? any input is appreciated