I have been trying out this tooth brushing powder. One of the ingredients is ground bone so eggshells might offer something similar. I've been thinking about adding this powder to my homemade toothpaste recipe which is equal parts coconut oil and baking soda plus some olive oil (to create a more paste-like consistency) and some peppermint oil. I currently find it annoying to apply the powder to the brush seems to spill everywhere. I'm probably just doing it wrong though...