Yellow and grey lines between 'old' teeth

[Black.bird]

Okay well-groomed folks, I have a tricky one for you:

How on earth do you get rid of the ugly yellow and grey lines between 'old' (natural) teeth?

- they are NOT dirty (this photo was taken post- a professional clean and polish).

... also, the photo has come out weird and fuzzy but the teeth are actually far whiter (have been professionally whitened) in reality. Haha - sounding very defensive, I know. Apparently putting extra whitening in between the teeth to deal with the marks is not an option.

 

[Snippysnips]

Teeth are naturally yellowish, it's the enamel that makes them appear white, I'd say try an find enamel repair an protect toothpaste but I don't think it's ever going give a brilliant white, it will just stop the enamel from wearing down as quickly