Do you always need antibiotics for a teeth/gum infection or sometimes do they go away on their own (self limiting)?

Infections in the mouth caused by not brushing and flossing and rinsing properly do not ususally need antibiotic cover, in fact they are discouraged. Antibiotics can temporarly cause an imbalance to the normal compliment of bacteria in the mouth, and you can get oportunistic infections which can be hard to treat like fungus and yeast infections.

Oral infections don't go away unless they are treated properly .An infection is a disease that must be treated by the dentist whether it is a gum or nerve infection. Many times antibiotics are used depending on the severity of the infection or if the teeth or tooth is extracted and are there any medical problems. This is considered the standard of care.