What can i do to to completely numb canker sore pain for a short time?

Anesthetic injection: If it is severely painful, a longer acting injected anesthetic like Marcaine can be used to relieve pain for 2-3 hours. If this is the first time you have a canker sore, you might want to have a dermatologist examine you and possibly do a viral culture to make sure it is not a cold sore (herpes simplex eruption). If not viral, a strong topical steroid may help heal it.