If you speak to your GP (if over 18) or mental health team (regardless of age) they can sometimes give you a short course of anxiety medication, it seems to help me a lot, if you're in a bind, you can always ask if the dentist themselves offers anything that could help.

Yes. Maybe something extra to relax you as the above comment suggests. Perhaps a trust friend or family member could come with you? Or, ask if they could have a therapy dog come in to keep you company?

I have this too. Only my dentist uses laughing gas through a thingy over my nose. It makes me more relaxed and a little out of it. That plus my audiobook through headphones and I shut my eyes. I do everything I can to relax and keep my mouth open wide (this means they can finish faster). I also have hand signals with the dentist. Ie waving hands means stop right now. When asked how I'm doing I do thumbs up for good, thumbs down for bad and in between for I'm struggling. We also take little breaks when I need it to help me cope. What country are you in?

If it's legal Where You Are, try CBD ahead of time. I wouldn't recommend THC obviously because of driving and also I don't know how old you are but if you are under 25 it can cause issues. Just double check that none of the medications you're using will negatively interact with it.