You certainly could use a straw if you choose. I have never had any one tell me that their teeth felt rough after drinking the Ortho Phos and Apple Juice combination, but it possible.
Ortho Phosphoric acid is a bone softener, so you should use caution with it. In the dilution and amounts recommended for the Liver & Gall Bladder flush, we have never had any kind of a problem. In fact, Food Grade (in soda ect.) Ortho Phosphoric Acid is an 85% dilution, that is almost triple the amount in the Ortho Phos product.
If you use a very natural unprocessed Apple Juice with the Ortho Phos, you will be getting a lot of natural sugars and pectin from the quart of Apple Juice. The sugars can sometimes cause teeth to feel “furry” or “rough” as well.
You should do what you feel best about, you know your body better than anyone.
