Wouldn't it be more convenient for the oral surgeons to collect one big jar of teeth for a school rather than having 5 or 6 different jars sitting around and students calling in all the time asking for teeth? Oh, and how come if a person dies and isn't listed as an organ donor, noone can have the kidneys... but if someone gets a tooth extracted, it's no problem to use it for study?
Anyhow... to answer your question, I would start now because they don't usually keep stockpiles lying around. You'll take in a jar and they'll collect them as the extractions are done. I'm going to 3 oral surgeons tomorrow with name-labeled jars containing 1-4 dilutions of bleach.
Happy hunting,
Dan