best dentist I've found is diagonally opposite Chao Paya Inn / Jomsurang post office and between an optometrist and English language school on Mukhmontri Rd. Very professional, clean and if you require it, there are one or two staff members who speak pretty good English. Go early though as it is always busy.
Polish and stain removal (coffee and nicotine) 400baht last time I went there.