I’m living in East Asia. A few weeks ago I noticed a brown patch on the side of my very back upper molar on the left. I went to the dentist in a complete panic expecting to need a filling, but although she found the tooth decay (at least that’s what I assume it is) she seemed at a loss to know what to do. She put a tiny camera in and got this picture which I’ll attempt to attach. I was horrified as it looks horrendous to me
but she first tried to say it was just the colour of the tooth and they can clean it, and then that it was “just some tooth decay” 
She did an x-ray as well and it looked clear to me (obviously I’m not an expert!).
She gave me the number of one of their dentists who speaks English so that I can go back and see him, but so wanted to be armed with some advice beforehand!!
So my question is, if it’s surface decay, how does a dentist usually treat that?