Let me explain how teeth work. Your tooth has three layers. The outer layer-- the part that you see-- that's your enamel. That's the white part. It's very hard and it rarely wears away, except it can wear away by mechanical abrasion, or sometimes foods with acids can do it. The layer underneath your enamel is called dentin. It's a very yellow layer, and that will show through when the enamel wears away over time. Inside your tooth is your nerve. That's the pulp where the blood vessel also exists.
Now your root is covered by something called the cementum. It has no protection against sensitivity, so any time a fork or a piece of tinfoil touches your root surface, it's extremely sensitive. Again, anything that is not covered by enamel is sensitive. And that's what causes tooth sensitivity.
So if you have a cavity, it's sensitive because your enamel is gone. If you wear away your tooth by brushing too hard, that causes sensitivity. Now there is a problem today because many mouth washes are extremely acidic. And you can search the internet to find many studies which show the acid level of many mouthwashes. That's measured by pH, a very low pHs are acidic.
Now it turns out, one brand is not acidic at all. And that happens to be TheraBreath. And TheraBreath now has something called Soothing Oral Rinse which continues the antacid line of formulas, but this one contains chamomile, oatmeal extract, xylitol, which not only acts as an antacid to keep your mouth healthy, but it helps to rebuild tooth enamel and keep your mouth in its very healthy state.