Please keep an eye on your dog for the next couple of months!!
Our lab was bit by a Copperhead in the mouth area. His head swelled up and he eventually was fine. About a month after the bite, we noticed his bark was hoarse sounding. Then he started losing weight and was not eating. I took him into the vet and they thought it was a rotten tooth. We put him on antibiotics, and a week later, he still was not back to normal. I noticed he would try to eat, and the food would drop out of his mouth and he would be salivating alot (which did seem like a painful tooth).
We took him back to the vet thinking the antibiotic did not work and they put a camera down his throat. Turns out the snake venom deteriorated the nerves and muscles in his throat and head area and he was not able to eat or swallow even though he wanted to. We had to put him to sleep. I don't want to scare you or anything, but it was a shock for us. I don't know if there is anything that can be done if the situation is caught early or not.
Vet said it does not happen to often - but they have seen it once in a while.