日記156 : Tooth Decay

This condition is common, but I wasn't sure how to describe it in English.
The last time I went to the dentist for a regular check-up, they said there was no problem and my brushing was fine. However, when I got home and checked my mouth, I noticed that the backmost tooth looked decayed.
Of course, I’m not a trained dental health expert, so it might not be a cavity; it could just be stained. But I regretted not checking more thoroughly before going to the dentist.