Rinse with baking soda and water on Shabbos?

Question

Are you allowed to mix a pinch of baking soda with water and rinse your mouth with it instead of using mouthwash?

Also there are two way to mix it: place some baking soda on your finger/hand and drop it in your mouth, followed by as sip of some water; the other way is to mix it in a cup with a spoon. Is there a halachic difference in regards how this "mixture" is created?

The possible melachos/gezeiros involved are: making medicine, kneading, changing the form of an object, and possibly adding the final touches.

Answer 1

R Yisroel Pinchos Bodner (Halachos of refuah on Shabbos, p. 32) writes

One may rinse out his mouth on Shabbos with non-medicated mouthwash to freshen hhis breath and teeth. He may also use breath-freshening drops or strips, because removing an odor is not an act of healing.

Note this would not be permitted for a medical use (see e.g., here under July 13, 2015 and here under February 3, 2019).

Making soda itself on Shabbat is permitted, see here or here.

Of course, consult your rabbi before implementing anything you learn here.