How many cavities is it possible to get filled at once?

Quite a few...: There is no absolute limit to the number of cavities that could theoretically be filled in one session. In the real world, though, most patients and most dentists are constrained by schedules, stamina, and convenience. It is customary to provide fillings in "quadrants"--i.e., doing all the fillings in one quarter-section of the mouth at a time, for the sake of efficiency and comfort.

Depends on anesth: The only limit to the number of cavities that can be filled it how long the patient can be there and open their mouth, as well as the amount of anesthetic that can be given.