I had a case a few years ago of a baby who chomped at the breast and caused the mom tremendous pain and nipple laceration.  This was an extremely motivated mother, her 5th child, who had breastfed at least 2-3 years each child before. She nursed through it all, feeling there were no other options.  We used warm compresses, massage and chiropractic care and there was great improvement after about 6 weeks.

The important part of this case is that it turned out that the baby was Down's.  He didn't have the classic appearance, so both I and the ped missed it for a while. My point in all this is to alert all of you that this MIGHT be the cause or other neurological problems.  When I have a baby now that really chomps, I do make sure to contact the ped to alert them to do a thorough neurologic screening. This has proven to be an important signal twice after this case.