How long before an abcessed tooth heals while taking an antibiotic?

As an Oral Surgeon's Assistant, I can tell you that the previous answer given is completely wrong! It does not take several weeks or a month before an abscessed tooth heals while on antibiotics. It only takes 2-5 days for healing to begin depending on the antibiotic you are on. On a strong dose pack of 3, it may only take 2 days. If it is a 7 day or more pack, you may not start to see healing for 3-5 days. You will start to notice the healing when the swelling starts to lessen and any pus or leakage begins to disappear. NEVER stop taking the antibiotics early! Always take the full prescription until they are completely gone! Many people quit taking them before they finish the whole dosage because they start to feel better or healed up. However, if you quit early, not only can the infection come back but could come back worse than before.
Many times, you may still experience pain after you completely finish your antibiotics because the pain is not from the infection but usually a large cavity in the tooth. You will want to get the tooth repaired as soon as possible after you are completely finished with the antibiotics.

That really depends on multiple variables but it can range from a couple weeks to several months.