I wasn't able to see a dentist until I was about 16, at which point I required
a lot of fillings. I lost count. It wasn't that I had terrible oral hygiene or something, I don't know why I needed so many.
I can sympathize with choking on the tools. After having a lot of teeth pulled, a lot of fillings, and three years of braces, I can say that all the tools in my mouth set off my gag reflexes more than once and there were countless times I felt like I was
about to gag. The best thing I can recommend is to keep your tongue far back in your mouth, take deep breaths, relax, and try to think about something else. The more you focus on what's going on in your mouth, the more that "aaaah too much stuff in my mouth" panic goes off. If there's music playing, focus on that. Try to recite another song in your head, mentally write a story, make a to-do list, just try to focus on something else. If there's no music, bring your MP3 player and some earbuds and ask if you can listen to it during the procedure. Just be sure to keep the volume low enough that you'll still be able to hear any instructions from the dentist, and keep your finger on the volume control in case you can't.