Actually, an almost identical question appeared on usenet a while back, so I'll just copy and paste (answer was by Gordon, I'm sure he won't mind
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>Can anyone help? I had a local anaesthetic at the dentist on Friday morning. The injection hurt a lot more than it had in the past and almost immediately my jaw joint felt stiff so that opening my mouth felt odd."
"Most likely the dentist managed to deposit some of the injected solution under the periosteum, it's a thin membrane covering bone. It tends to tear the membrane a little and produces some swelling and pain. Alternatively, if you felt a little electric shock at the time then the solution was a bit too close to the nerve, similar result.
> Is this a usual side effect or an unusual complication? Is it something that can always happen or did he not do the injection well? And please tell me what I should do now? Should I rest the jaw or move it a lot? Which will be best in the long run?
"It's a relatively uncommon consequence of getting a local anaesthetic injection. It can happen at any time to any dentist, it's absolutely nothing to worry about unduly and it will get better in time.
Treat the joint sympathetically, move it about gently and apply an ice pack to the area outside the joint. Try to take lady like small bites of food, and nibble instead of gulping. (Of course, I'm sure you always eat in a ladylike fashion anyway!).
Ibuprofen will help a lot if you can take it, Paracetamol will do instead if you can't.
HTH
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Gordon
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Don't really know if there's anything to add to that... it sounds pretty similar to me
