Ive had similar issues with different types of toothpaste and the type of toothbrush to use.
I tend to gag if the toothbaste is not minty enough or too sweet, some toothpaste can also be a problem if it produces a thick texture in the back of the mouth or paste that has a habit of changing its flavour.
The toothbrush can be a problem as well, it hast to be a soft bristle and electronic to avoid the sound and feeling of brushing a manual toothbrush makes. The toothbrush must also be time programmed to seek how long to brush where and when.
All I could do is experiment with different toothpastes and toothbrushes until I can find something more tolerable. I often rinse with water or a non-alcoholic burn free and flavour weak mouthwash.
Otherwise there's days I can't brush at all and have so far managed every other day at most to twice a weak at the very least as before I could barely manage once weekly, to a similar affect with basic general hygiene.
A Dentist may be able to give some advice on toothpaste, toothbrush, mouthwash and alternative techniques. Mine does often advice on flossing, but I can't for the life of me do that as the feeling of teeth being pushed away and discomfort feelings I get with that.
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"When you begin to realize your own existence and break out of the social norm, then others know you have completely lost your mind." -PerfectlyDarkTails
AS 168/200, NT: 20/ 200, AQ=45 EQ=15, SQ=78, IQ=135