Dr. Campbell-McBride says: 
"Your teeth are sensitive because the enamel on them is too thin and is poorly nourished. So, I recommend that you stop using all toothpaste and replace it with olive oil: dip your toothbrush into good quality cold-pressed olive oil and brush as usual; rinse with water. This is based on an Aurvedic procedure called 'oil pull' which has a good ability to detoxify the mouth and initiate healing in your teeth and gums. Brush with olive oil twice a day. To nourish your teeth you need plenty of animal fats in diet and vitamins A, D and K. The animal fats will provide large amounts of those vitamins, but to add more you can take a good quality cod liver oil (preferably fermented). Sour cream made at home from raw organic cream will heal your enamel quite quickly.
While you are healing your teeth, reduce the amounts of fermented vegetables in your meals and drink their juice instead (added to soups and meat stock).", GAPS FAQS