I have good teeth, and am lucky to have had good dentists. My dentist, even though I dread going, is very nice, and calls me hunny bunny, even though he is an adult dentist and I am an adult. So I think often it can be a matter of finding the right match, definitely Ive tried dentists that I never went back to after once.
I had braces as a teen, and didnt really have a choice about it because I had four teeth removed because there was no room for them. The braces were awful, and after they were off I dreaded having the bottom retainer taken off, so I avoided having it done until it caused problems hurting my gums.
If someone I cared about couldnt brush their teeth I would suggest trying to use a mouthwash twice a day to avoid cavities. If mouthwash is out of the question (some burn more than others), I would suggest at the very least trying to find a sensitive toothpaste, and use your finger to get it on your teeth twice a day and rub it around and then rinse it out. Or they make those disposeable "brushes" on a stick that are a soft sponge that is round that you can use.
At the very very least, you could wash your mouth out with water after you eat or snack or drink a pop so that the food doesnt stay in there and erode the tooth.
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Your Aspie score: 165 of 200
Your neurotypical (non-autistic) score: 48 of 200
EQ 12 SQ 70 = Extreme Systemizer