Any experience with breaking teeth?

[hmpf]

I haven't had a single cavity in my life yet, but I do seem to have unusually brittle teeth. The tip of one of my bottom front teeth just broke off - and the two teeth next to it have been broken for years, so now there's three broken teeth next to each other there. There's also a broken top front tooth (although I think that particular one was broken in a legitimate accident, years ago). I'm finding this a bit alarming (not to mention more and more unsightly)... especially as with today's tooth, it happened while I was neither eating nor gnashing my teeth or anything like that. I mean, if my teeth are so brittle they're breaking even without provocation now... o.O

Calcium deficiency?