My son is 3.5 years old and hasn't yet been to the dentist - we're going next month as a family and the dentist will try and do a cleaning if DS is cooperating (I'm doubtful he will....but he may surprise me!) :-)
While it's not the same thing, DS still can't sit still for eye exams (he needs to have these on a regular basis due to an eye condition he was born with) - so his ophthalmologist must sedate him in order to do her examinations. I've heard of dentists doing this as well to be able to do dental work on children. It's not ideal, but you may want to ask about this.....keeping in mind that all children are different, and good (or bad) humour will vary day by day, so she must may cooperate after all.
The problem is the bonding stuff they have to put on the teeth isn't as strong as real teeth. And because it is an area where it takes a beating, so to speak, they are fearful that it would break off and could cause injury or just wouldn't stay anyway. I know in our town the normal family dentist did not "put the kid out" only the pediatric dentist would (they have to have some certification or something). I would suggest you see if maybe there is an office that does sedation on kids if it's that bothersome to you. As far as sitting still long enough for them to fill a tooth. Maybe 5 years? They hate all the noises and the invasiveness. It's terrifying for them.