Re: brown line on 2 teeth
Do you use tobacco? That will stain brown spots on your teeth. I had the same problem with my teeth from smoking cigarrettes, it could be another form of a stain if you don't use tobacco, and doesn't necessarily mean it's a cavity.
I had white fillings put in most of mine because the dental cleaning failed to remove the stains but they told me it wasn't cavities, that it was just the cigarrettes staining my teeth. But it just looked so bad, I went ahead and got the fillings.