How long would it take 800 mg amoxicillin twice a day to take affect for a abscessed tooth? i have some swelling in my face but its minor. i have a dentist appointment but its awhile from now?

Antibiotics control the infection but the symptoms may not immediately resolve. The source of the infection needs to be addressed. This tooth will probably need root canal therapy or extraction. The sooner the better.

Your appropriate antibiotic dosage will help control spread of infection but will not cure the cause, the abscess. Treatment will probably require either root canal/crown or extraction/implant/crown. Antibiotics should take full effect in 48-72 hours. Make sure to take the entire prescription, don't quit early. Sounds like your Dentist has your problem well in hand.