Bumrungrad clininc is still one of the best/safest, but their prices are almost western-like (depending on where you're from). My advice would be to look at a official lists of dentists recommended by governments and embassies, so while you may end up paying a bit more, the risk factor should go down as well. For example, Canada's list is here: http://www.canadainternational.gc.ca/thailand-thailande/consular_services_consulaires/dental-dentaires.aspx?lang=eng