I had to have an emergency crown replacement which involved some trimming of my gums (yick!) during this pregnancy. My OB and my dentist agreed on the following guidelines:
- Injectable anesthetics ending in "-caine" were all OKed (novocaine, lidocaine, etc).
- NO NITROUS OXIDE
- No systemic sedatives (no sedative pills)
- No pain killers afterwards stronger than tylenol without checking with the OB first before taking them
- NO XRAYS
In general, everything I read suggested to defer until the second trimester if possible, but agreed that emergencies need to be dealt with.
The dentist did not think I needed antibiotics, but the OB said that if he had thought I needed antibiotics, penicillin, amoxicillin, and erythromicin were OK, but NO TETRACYCLINE because it can have bad effects on the development of the baby's teeth in utero.
Obviously your situation may be more severe than mine was, and you should go by what your own OB says, but I ended up doing fine with some local lidocaine in the gums for the work I had done, and it wasn't something that I could have deferred (I threw a crown and so had a bloody naked stump in my mouth, it couldn't wait until after the baby came :)