The barber surgeon would have carried out the dual function of being both a barber in the traditional sense, including a offering shaving services and that of a surgeon or field doctor.
Medical theory and practice were crude in comparison to modern modern. A number manuals were produced to provide instruction to “Chirgurians” which offered weird and wonderful solutions to practical problems. For toothache the cure was to pull the tooth and roots from the patients jaw, with minimal anaesthetic (sack or brandy where available!).
The barber surgeon would also have been able to remove musket or pistol balls from his patients.