Vaccinations aren't required to enter Thailand, but cholera, hepatitis A and B, Japanese encephalitis and tetanus shots are a good idea. The mosquito-borne illness dengue fever is a problem, even in Bangkok, and malaria is present, though not prevalent, in some outlying regions. It's best to drink bottled water. Hospitals and dentists in major cities are of a good standard. They may even accept your health insurance, so carry proof with you (and if you know your insurance doesn't cover you abroad, buy travel insurance before you go, just in case).