Here is what I was able to find out by doing a little searching
Most dentists start with earnings around $60,000 and go up quickly, especially if they work for themselves. In 2008 the U.S. Department of Labor estimated that, as a national average, general dentists earn over $120,000 a year, with the highest percentage going to those who work emergencies and take weekend patients. The lowest salaries are earned by those who work in state clinics and general medical centers, with annual median salaries of $68,810. In comparison, the American Dental Association puts specialists’ median salaries at $315,000 per year.
Complete an Undergraduate Education:
Before future dentists can begin their professional training, they need to earn a bachelor’s degree at an accredited college or university.* There’s no specific ‘pre-dentistry’ undergraduate major, but many students hoping to go on to dental school choose to major in biology, chemistry or another science.
Apply to Dental School:
Hopeful future dentists must achieve good scores on the Dental Admissions Test (DAT) and have an above-average undergraduate academic record in order to be accepted at one of the nation’s 56 accredited dental schools. Competition is fierce, so most applicants apply to several schools at the same time.
Attend Dental School:
Dental school lasts four years and includes instruction in biochemistry, anatomy, physiology and clinical science, as well as a lengthy clinical component in which students attend to patients under the supervision of licensed dentists. Upon completion of dental school, future dentists are awarded either a Doctor of Dental Surgery (DDS) or Doctor of Dental Medicine (DDM) degree.
Earn State Licensure:
Before beginning practice, all dentists must become licensed by the state in which they hope to work. Licensure exams comprise written and practical components; the written portion can be completed by achieving a passing score on the National Board Dental Examinations. In 17 states, dentists who choose to specialize must also become licensed in their specializations.
Establish a Practice:
Most dentists own their own private practices. In order to build a presence in a certain location, dentists who have completed their educational and licensing requirements need to either purchase an established practice from a retiring dentist or open a new one.
As far as your question about orthodontics being the cheapest people when paying there assitant and hygienist. I think that would depend the dentist and is probably not a fair conclusion. I have also listed a link below for how much it all cost for them to become a dentist.