Here in the US, a dentist goes through at least 8 years of university before he can practice- 4 years of undergrad, most often as a pre-med, bio, or chem major, followed by four years of dental school, and a 1-6 year residency. Admission to dental school is cut-throat competitive- for example, in 2005 Stony Brook Dental School admitted less than 40 students, out of a pool of almost 900 applicants (although, to be fair to the American-educated M.D.'s out there, US Med schools are even tighter with their admissions, the same university's med school admitted 101 out of ~2600 applicants in that same year). The four years of dental school are extremely rigorous and comparable to US medical schools- indeed, some universities have their dental and medical students pooled together in the same classes for the first year or two, in courses shared between the disciplines such as anatomy and pharmacology, and later on during their education in shared disciplines such as radiology and anesthesiology. Dental school alone is a 200k-300k investment in the United States, without including the costs of your four years of undergrad. However, before you non-Americans start feeling sorry for the plight of the American dentists, please recall that they make a ton of money once they're finally through, and a good percentage are self-employed or work in small partnerships where they can essentially make their own hours.

In many other countries, dental school is a 4 year undergrad program that you go into right out of high school. Brush and floss, kids.

American dentists (along with the Canadians, who go through the same slog but never get the satisfaction of being associated with good teeth) are among the best trained in the world, with access to an enormous library of procedures and materials you'll be hard pressed to find elsewhere (though I've been told that Japan and S. Korea have exceedingly thorough and advanced dental education systems, comparable to what we've got here). It doesn't take 9 years to learn how to do a routine check-up, and routine check-ups will never pay off that 300,000 in college loans- thus American dentists offer a staggering array of cosmetic and lifestyle-improving procedures, that while not necessary for survival (my landlord has +/- 2 teeth and he's doing just fine, thank you very much), definitely become a quality of life issue, especially here in America where everyone looks at your teeth. This leads to some health problems, however, especially when you've got patients who waste their money on whitening and other cosmetic procedures, yet refuse to maintain basic hygiene and have seriously unhealthy gums and teeth that will fall out if they bite something harder than a chicken nugget.

Britain's NHS reports that 55% of British adults have some form of tooth decay, but didn't specify to what extent that was being treated. With that being said, an estimated 23% of American adults have untreated tooth decay going on in there. Medicare/medicaid doesn't necessarily provide adequate dental coverage, though there are a plethora of relatively low cost dental plans out there- however, getting some of them to pay is like getting water out of a stone, so someone with one of these discount dental plans might still have trouble getting complex and expensive procedures taken care of. Other plans exist only for kids, some offered by private companies and others public incentive programs. Thus, you have a pretty big disparity in the US between the teeth of those with private dental plans, and those without.