Yeah, a power float definately is a weapon of mass destruction in the hands of an inexperienced user. You can grind off WAY too much tooth if you don't know what you're doing, or can't SEE what you're doing.
This equine dentist I use also puts a special halter on them and ties it up to the top bar of the stancheon so that it that supports their head at the right height after the speculum is in their mouth so he has both hands free to work. It looks a HELL of a lot easier than having a 300lb horse head hanging on one arm, or on your assistant's shoulder while you try to hunker over and see up into his mouth. I just don't get it why my vet doesn't do that. I know that part of the reason is that he's nearly been brained by a horse with a speculum in it mouth, but I'd think that he just needed to be sedated a little more first. He also says that he can be done by the time he gets all that contraption on, but I keep thinking "yeah, and how good a job are you doing by getting done that quick?". So I guess he has valid reasons, to him, but I'd just rather use somebody else for that particular service, even if it means I gotta trailer an hour.
The horse, NOT the vet! ;o)