Thanks for the information about baking soda. I didn't realize it was harsh on the enamel. Actually, what I just read, is that the baking soda is harsh by itself (relatively speaking), but when combined with water in solution it's not as harsh - maybe considered even actually mild as an alkali solution. Possibly that's why I haven't had any problems with it. I mix a small amount of water with the baking soda. It doesn't take much to draw it into a solution.
I've had other toothpaste that made my teeth quite sore. The baking soda solution I use seems to be OK, but I'll read more about it, and switch to something else if it seems to be harmful. If it's harmful in the long term, then maybe using baking soda solution for a short time only might be recommended as a whitener and cleaner.
It's interesting to read about tooth enamel. Some people will say that the enamel won't repair itself, yet other people will say that it will. Over and over again, I've heard that even small cavities that don't break the surface of the enamel into the dentin can be encouraged to heal itself without any fillings. There's so much conflicting information out there, so it's hard to know who to believe.
But anyway, there seems to be a general consensus, that when baking soda is used by itself, that it can be too harsh for the teeth. That's nice to know...so I'll make sure that I continue to mix it in water, if I want to remain using it. I only mixed it with water by chance...seemed like a good thing to do at the time. So, I guess I was lucky.