This snake I found/rescued has some scales missing on his head. Do they ever grow back when they shed their skin or anything?

Also I have noticed a lot of the time when I am sitting by the tank watching him he will come closest to me and open his mouth. It almost seems like he is struggling too or yawning. The left side of his mouth opens faster then the right. The right side is also the side with the damaged eye. I can not see any teeth either. I don't know much about garters but I thought I should be able to see some teeth?