@ZipLine-- Actually, I have heard that oral numbing medications can be dangerous for babies. I believe the FDA even released a statement on this at some point. So I don't think it's a good idea to use them on a teething baby either.
Have you had any luck with teethers? I do recommend those that have water in them and can be frozen. They did wonders for my daughter when she was fussy while teething. A baby that cries a lot while teething is probably dealing with a lot of inflammation and pain. Cold helps relieve both issues.
Also, make sure that your baby is healthy otherwise. Sometimes teething can cause a mild fever and some parents ignore fevers for this reason. But a constant fever or fever higher than 101 degrees is not normal. So rule out any other possible problems.