The level of tooth sensitivity I have can fluctuate rather quickly depending on changes I make. The first was lowering the amount of sugar I consume, big improvement. The second was supplementing with 5,000-10,000 vitamin D daily, big improvement.
But even after these, if I ate a few too many apples in a day, my teeth got a little sensitive. Not as bad as before, but still enough to be annoying.
I started supplementing with magnesium a couple weeks ago, and my teeth are not sensitive at all. I'm unsure if this is the main cause. I've been trying to up my iodine levels recently by consuming more kelp, and I think this has increase my saliva production. And our saliva naturally improves our bacteria levels in our mouths, and it is needed for re-mineralization of enamel.
I can feel that my teeth aren't as sensitive when I'm brushing, it's like I can't "feel" the bristles as much. Take this for what it's worth. I thought I'd throw this out there, because I know some of you have problems with sensitive teeth. The type of magnesium I'm taking is called magnesium glycinate.