Why does salting a canker sore or wound numb the pain for awhile?

Not sure it does: Salt powder directly on a canker sore will hurt more and perhaps divert your awareness from the underlying issue as it fades over time. Dilute salt water will often promote healing but isn't very effective as an analgesic. There are far more effective ways of controlling pain than salt..

Placebo: Canker sores are the most common oral lesions. Individual ulcers typically last 1-2 weeks. The aphthous ulcers are usually self-limiting. Try to keep adequate oral hygiene as possible. If concerned see your dentist after 10 days or visit today for laser immediate amelioration. Salt can not help canker sores heal faster.