Adding a little bit to Ship's reply, your exposed roots can be sensitive because they are porous. If you brush with a toothpaste for sensative teeth that contains potassium nitrate, it fills in the tiny holes in your roots and make your teeth less sensitive. There's also a kind of coating that the dentist apply to the exposed root that seals it. That seems to work pretty good.
After my wisdom teeth were surgically removed, (I think with a chain saw) I had permanently exposed roots. It took awhile, but the discomfort did go away.