from a dentist point of view, which always takes forever and doesn't work for me anyway.
Do you have red hair? My husband found dental anesthetic worked so badly for him that unless it's a very bad cavity (or wisdom tooth removal), he asks it to be without anesthetic. He'd get the shot, and the shot would hurt; then he'd have the drilling, and that would hurt; and then the pain from the drilling would stop, but the shot site would bother him all day.

We have heard within the past few years that apparently redheads have a very different reaction to anesthetic from most people: many need a significantly higher dosage for the stuff to work!

(Then there was my wisdom tooth removal, where the doctor was like seven feet tall, and I'm short, and he remarked on how tiny I was, gave me anesthetic, told me to wave if it wasn't enough, and then kept telling me to hold my hands still while I was frantically signaling that it wasn't enough. He did fix that, but then prescribed half a pill of painkiller every X hours for after the removal. I needed a whole pill. I just looked so small to him that he wouldn't give me enough!)