Is sulfamethoxazole good for tooth infection?

Not especially: Augmentin (amoxicillin and clavulanate) or Clindamycin would be better choices.

No: Usually penicillin or Erythromycin family of antibiotics are best.

Tooth infection: In my opinion Amoxicillin would be the first drug of choice. There are good alternatives for patients with allergies to this antibiotic. I hesitate to also list these alternatives in case you are trying to self-medicate yourself. The treating dentist know best how to treat and what to prescribe based upon the medical and dental history and the specific circumstances. Antibiotics do not cure!

No: There are more effective antibiotics for tooth infections, the choice of which is determined by the dentist based upon dental and medical condition of the patient. But antibiotics only confine and contain the infection. A dentist must be consulted to determine the cause of the infection and direct treatment toward the source to resolve the infection safely and efficiently. Call your dentist.