What does it look like if the crestie doesn't have sufficient calcium reserves?

I've been able to see the two white "pouches" in each of my cresties' mouths, but I'm just curious as to what it looks like if they don't have enough calcium in their diet. Are they smaller in size? Not there? When's the time to worry? I know that my cresties are getting calcium in their diet, but I would just like to know before breeding.