Rav Linzer, What are your thoughts about using “whitening toothpaste”on Shabbat? If whitening toothpaste is permitted what about a whitening gel that is not toothpaste but is applied for a few minutes and then washed off as part of a daily ongoing treatment to whiten teeth? What about general care of teeth like flossing? I am not asking about brushing teeth on Shabbat because I assume you follow those who permit it, but if I am wrong please correct me. Thank you.
Let’s bracket my own position re toothpaste. For those who use it on Shabbat, I don’t see a problem with whitening toothpaste. From what I can tell it doesn’t actually whiten, it just cleans them better. https://www.mayoclinic.org/healthy-lifestyle/adult-health/expert-answers/whitening-toothpaste/faq-20058411
Flossing. No problem if you precut the floss and it generally doesn’t lead to bleeding of the gums. Whitening gel – from what I see this contains bleach. As such, it would be forbidden as צובע.
Regarding the whitening toothpaste, even if the toothpaste does not actually whiten, does it matter if the person buys the whitening toothpaste thinking that it is actually whitening the teeth?
No. Does not matter. But you should explain why so that he understands the halakhic issue.