Hey,

I actually have this exact problem. I don't have a great gag reflex, but specifically when brushing my teeth it is absolutely atrocious. Like I will be brushing my front teeth and gagging, and then I will get sick brushing my tongue, and since I do that twice a day this is a very regular occurrence for me.

I have found a few things to help: certain toothpastes trigger this less than others, potentially something in them is part of the cause, like a sensitivity? (Though there is also a bit of a trauma element to it as well). So try different textures/types of toothpaste.

Another thing to try: when brushing your teeth, take the hand you are not using to brush and ball it tightly into a fist. This works a bit better if your thumb is actually inside of the fist, because what you want to do is focus on clenching and exerting pressure on your thumb (if this is painful or uncomfortable then just focus on clenching into your palm). You're not trying to hurt yourself, but to ground yourself by focusing on a very strong sensation other than the toothbrushing.

A calcium tablet taken before brushing your teeth can help reduce acid reflux caused by severe gagging.

Pick a tooth-brushing song. A song you can sing in your head/hum that takes about as long as you want to be brushing your teeth for. And then sing it in your head (or hum along depending how able you are to do that while brushing) to keep your mind off the sensation of brushing.

Whenever the gagging starts up, relax on whatever part of your mouth you are brushing and shift gears. If you were going soft and slow, move to different teeth and be vigorous (or vice versa). The point is to shift the sensation causing the gag to a different sensation.

Try to brush at least the front of your tongue. If you start getting intensely gagged, stop and then try again the next day. You want to be able to train yourself to be used to the sensation so you can more comfortably brush farther back.

Do not brush your teeth shortly after eating. If you are feeling bloated/very full, wait longer, or do some exercise or something. While bloated/very full your gag reflex will be worse and you are more likely to trigger reverse peristalsis (vomiting) from gagging.

None of this has made the problem go away, but I can successfully thoroughly brush my back teeth and even the back of my tongue multiple times daily, with only occasionally being sick, and with relatively minimal gagging (some days are worse than others of course).