As a hospital nurse, we used to use halcion a lot as a sleeping aid, but honestly we haven't used it in a number of years. I would be concerned about driving to and from the dentists office under the effects of halcion since it is a sleeping pill.
Here is an article I found for you - they seem to be calling this "oral conscious sedation" which is very concerning in a dentist's office and not in the controlled setting of a hospital (if you needed to be intubated or resuscitated for an adverse reaction). According to the article, they haven't seen any problems with adults before, but I certainly wouldn't want to be the first.
http://www.msnbc.msn.com/id/5446489/
I sympathize with your fear of dentists. But personally, I'd try to find a safer route to effective dentistry. Off the top of my head, I don't know what other options you have. But maybe someone here might know. Is there somewhere like a hosptial setting that does dentistry under anasthesia or intravenous conscious sedation? What about gas - is that still being used? I remember having that myself as a kid.
Good luck in whatever you decide.