Today's visit to the dentist only left me with about three and a half hours of numbness. Explained to him what happened last time, and he had me massage the place he injected for about a minute after he injected it. Last time, I guess the stuff basically didn't circulate over to the liver to be taken care of very quickly, so it stayed numb for quite a while (three and a half hours is still a bit longer than expected, but much more in line with what it should be).
Time for a nap.