Hello, back as promised!
OK so first of all I just wanted to say again, well done for telling them! I promise I'm not just saying this, you really are doing amazingly well - you've already taken the first steps by coming on here and then by telling your parents, and despite encountering obstacles you're still going, taking the initiative and doing something good for yourself. So give yourself some credit here! You are much stronger than you think x
It sounds so much like a lot of what you need is confidence. Remember, you're scared but you're still here, still doing it - ultimately it's what you manage to
do that matters, not how scared you felt doing it. Don't beat yourself up over that.
Re your parents - I do still wonder if there is anybody else you could ask to come with you for moral support? A friend, or another relative? It may be that your parents are just not best placed to support you with this. If they did come, would the support they gave be helpful to you?
Also remember what I said before - when you get there, the staff and the dentist will be able to support you - you won't be doing this alone! They are there to help. And there will be plenty of people here rooting for you!
So, you're 21 (I think?), and you've already taken the first steps towards taking control of your own healthcare/dental care. Remember, your parents are not in control of your dental care...
you are. It's your own choice to do this, and you're making the right choice for yourself. You are so much stronger than you think, and you are doing so much better than you think! I know it's scary stepping out into the unknown, but you've got this, and you have help from us here. The dentist will treat you like an adult too, it's not like it was when you were a kid - when you are in there, you are in control, always.
Finally, if you still feel your parents are your best bet (only you can know this), then maybe the way in is to show understanding that you have this shared fear, that you know where they are coming from. Find some common ground and then work on it together. There's room for mutual support and understanding there, if they're up for it!
Do give some thought to whether you could ask a friend instead though!