For the longest time, I have wondered why it's impossible to get a dental appointment on a weekend. My only answer is that if all dentists worked on the weekends, it would increase the supply and lower the price they can charge.
I thought dentists took an oath to serve the public. It seems to me that a dentist who really cared about the dental hygiene of a community would try to serve as many wants and needs as possible.
Here's a Yahoo! answer:
A lot of dentists work 10-12 hours per day. The office I'm at is open from 6:45 AM - 5 PM Monday through Thursday. That is over 10 hours per day. While there is no law about how much a dentist can work, or what days the office can be open, working 12 hours a day can tend to be rough. Most metropolitan areas have emergency dental clinics that are open 7 days a week. Try looking for one of them.
It also isn't about money and not having to work because you make so much of it. It's about busting your hump and allowing your staff to have a break.