Thank you, Tyler and Rebecca, for your replies!
Tyler, I agree that I will need to double-check with a dental professional before making said tooth powder. Thankfully, I used to work for two dentists right here in town for a couple of years, and I know plenty more around these parts, so I'll be sure to double-check the abrasiveness factor of the ingredients.
Rebecca, thank you for your helpful response. Out here in Wyoming, I will need to be hauling water and will be using it sparingly, but as you said, it takes forever to get through even a tube of conventional toothpaste, so I'd imagine the minute amounts wouldn't do much to the soil. And, on second thought, I think you're right about bentonite clay and dolomite powder not actually containing much salt, but again, I will be sure to double-check that with local dentists.
I appreciate all of your help!
Ashley