OP, I would ask around the special needs community in your area to find a dentist who is special needs friendly. This is how I found my dd's wonderful dentist, after we were 'exit-ed' from another dentist. I drive an hour to this dentist and it's totally worth it.
We have gone from the dentist/hygenists working on dd with her standing (and squawking), to me laying in the chair and dd laying on me (like the papoose board, except I'm the board), to dd calmly walking in and getting into the chair!
When we first started there, she had work needed and we sedated for that. Haven't needed any since so I'm not sure how we'd handle that, I assume we'd try gas first.