Why is my lip swollen and blistered inside after a dental procedure?

Lip swelling: It sounds like you may have accidentally chewed your lip while you were still numb. This is fairly common. Sometimes people chew their cheeks or tongue.

Most Likely a Bite: Most of the time when you have a sore or blister after dental work it's because you accidentally bit yourself while you were numb. This is quite common. It can happen while you're at the dentist or afterwards. Some people's oral tissues are quite delicate, so it's also possible that you're having a reaction to where the dentist was holding your lip/cheek, or pressing on an area, or gave a shot.