The mot recent survey of dental school tuition shows the average is about $21,000 per year for residents. For non-residents, the tuition rises to $32,000 per year. This data is from the ADA Survey Center 2004-05 Survey of Dental Education. I remember when I was in school there were costs other than tuition like a good bit of dental instrumentation and supplies you had to purchase. Private school programs can be quite high. The University of Pennsylavania tuition is over $48,000 per year! Most public university programs are less than the averages printed here:
Here is a link to the University of Alabama School of Dentistry web page on estimated tuition and fees.