jaw pain after injection

The last 2 times I have received an injection to have dental work done I have had pain in that jaw and joint for MONTHS afterwards.  Both times were after having cracked a tooth and having it crowned. The first time on a bottom left molar and this time on a bottom right molar.  The first time the pain persisted for 10 months on my left side!  My dentist thought I had TMJ, but the mouth guard he made me did not help one bit, nor did antibiotics.  Finally the pain just went away.  

My second crown was done on my right side and now my right joint and jaw ache.  This time the pain has lasted 1 week so far.  The dentist did several injections and a few were painful while he was doing it.  Then after getting home I was numb for 4-5 hours.  Once the numbness wore off my jaw and joint have ached ever since.  It hurts every afternoon around 1:00pm and again around 11:00 pm.  After I take 3 Motrin the pain takes 30 minutes to 1/12 hours to go away.  The dentist ground the crown down and I do not feel it touchign the other teeth.  

Could I be having an allergic reaction to the anesthestic or did my dentist hit a nerve or bone both times he injected me?  I have had some pain in previous years after dental injections, but none that lasted more than a week or so.  Could it be possible for me to be allergic to the medicine and therefor each time it is used I have more problems?  Any advice would be appreciated!

[Jerome Tsang, DDS]

Its rare to have an allergic reaction to anesthetic.  If it was, it probably wouldn't be isolated as just pain.  

Its possible that the muscle was injured during the injection.  Nerve damage usually results in more of a numbness or tingling that won't go away.