How fast can a tooth infection come back after 10 days of penicillin?

Variable: Depends upon the location, type of infection and the causative organisms. Could be very rapid if there is an abscess.

1-2 days: Sometimes the infection is contained, but sometimes it can return overnight.

If a tooth is infected, antibiotics will not permanently cure. They may reduce the extent of the infection and slow spread to other organ systems, but will not remove infected tooth material. For that the infected tooth material has to be removed, either by root canal treatment or extraction.