I'm wondering how long does it take to get numb for an extraction?

Immediate ~ 20min: Upper teeth tend to be easier and faster to get numb. Lower teeth, depending on where your nerves are running--high, or low, or average middle--it may take a while to get numb. If a dentist can give you a very slow, painless injection (will take 2 minutes or so per cartridge) you may notice you are already numb---it all depends on many things. I hope i answered your question, if not, try again plz.