What does the dentist do for a gum infection?

Many options: Really depends on what is causing the "infection" it may involve better hygiene or more involved hygiene by the professional, rinses, antibiotics or even surgery. It all depends on the cause and severity. See a dentist or even a periodontist if it is severe. The dentist will also make sure the infection is truly gum related or possibly due to an abscess from a dead tooth. Then see an endodontist.

Varies with severity: If the infection is limited to the gums, instruction in home care along with a cleaning may be all that is necessary. If the infection affects the bone also, treatment can be more extensive. Use of antimicrobial, removal of plaque, tartar and bacterial toxins in the root may be necessary. A laser may be used to kill bacteria and get tissue regeneration. Nutritional supplements may be necessary.