This was probably done without any kind of pain killing anything, besides (just guessing) alcohol. It must have been absolutely excruciating for weeks, before the jaw healed. Unbelievable.
Apparently (from the summary of one of the articles) opium has been used as a pain killer for a very long time, and the Byzantines used laudanum.
https://rhm.sums.ac.ir/article_45640.html
Maybe they knocked the guy out with laudanum before the procedure, which would have made the whole thing much easier and far less unpleasant for the patient.