I'm surprised this remedy isn't up already on the tooth abscess section: Red onion. Actually, any onion will do, but red onion seems to work the fastest. Slice up a raw red onion, bit by bit. Hold a slice in your mouth and chew slowly for about 15-30 minutes. Repeat as necessary. The pus and phlegm should drain right out, and the inflammation should go way down. It worked like magic for me. I was experiencing severe pain to the point of shooting pains into my skull and through my jaw, even starting to go down my neck. (eek!) This stopped the infection and the symptoms dead in its tracks.
Onion skin takes away pain and swelling on tooth abcesses. I used a peeled piece of onion enough to cover the abcess.