universities between uk and usa

It depends on which university you've specifically chosen. There are still some renowned universities in US. However, as a whole in general, I think and I prefer those in UK for dentistry.

You can find some questions and answers in the following web site regarding your queries in studying dentistry.

http://forum.rocsaut.org/topic_show.cgi?id=10709&h=1&bpg=1&age=30

Of course, UK is wellknown for such course, many big universities offer the 4 years programme. You can find more details in this site:

http://www.britishcouncil.org/learning-infosheets-dentistry.pdf

It's a very competitive programme, the entry requirements is also very high (generally 3 straight A grade in Science related A level examinations), plus written and oral interviews. Good luck!