I think the OP was talking about Post-graduate Education, not necessarily obtaining licenses in the respective countries that he/she had mentioned.
USA: You basically need to check each institution's program and find out what their requirements for entry are like for foreign dental graduates. Of course, this may mean that you would need to have completed GRE, TOEFL, and maybe NBDE Parts 1 and/or 2. They all have different views on things involving international applicants so it is better to contact each institution rather than relying on second-hand info.
UK: This is probably similar to US. You need to prove your English competency. TOEFL may be accepted but they may prefer IELTS. GRE may or may not be required. Nowadays, it is mandatory to have MFDS if you are aiming for a clinical specialty. You may not need to have MFDS if you are only going for research-only programme.
AUSTRALIA: Similar to the US requirements. You need TOEFL or IELTS for English language. Some may prefer you to have a Fellowship in one of the Royal Colleges of dentistry (e.g. MFDS or FDSRCS) or have completed Part 1 of the FRACDS.
You must also take into account of the immigration laws/student visa regulations and the tuition fees for international students. It can all add up to quite a bit. None of these post-graduate programs gurantee that you will find a job and the necessary immigration papers in the end. So if you want to work and live in any of the countries mentioned above, you must consider the immigration factor as well as where you would like to establish your permanent place of residence.