The enamel of the teeth was made long ago. It can be eroded away with acidic foods or chronic vomiting.
The most common calcium leaching occurs at the root, and those teeth will become loose if calcium is lacking for whatever reason.

The body will "rob" the bones if there is not enough serum calcium to run the heart and nervous system. I am not really aware of the teeth going to save the bones. But it is possible.

Steroids are major disruptors of bone metabolism.

I think people are generally aware (and so are doctors) about taking calcium now. It is added to common foods even.
But Vit K and B12 are still neglected. So is magnesium. And the mineral boron. We are just learning that almost 1/2 of US population is low in Vit D. I think the Vit D connection is the most critical link at this time.

On the links at PN there is a link to .gifs showing how the various osteoporosis occurs... let me see if I can find it quickly.....

........ok ...I found the link. This link shows animations of how bone is torn down and reformed, and how that process is affected by drugs and life conditions:

http://courses.washington.edu/bonephys/opmovies.html

It is interesting, and you should attempt to watch them...if it seems difficult do it more than once. You will see how bone is remodeled. (and not).

Common drugs I think are also serious culprits. The information about SSRIs is daunting and very new. Millions and millions take these drugs...and have no clue that their bones are suffering, as a result. Same with proton pump inhibitors like Nexium, Prilosec, Acifex and Protonix, and Prevacid. We are talking millions and millions of people!