Teeth are porous and will stain over time no matter how well you look after them. Even crowns and veneers will stain on the surface. There are a few substances that stain white teeth considerably over time. Regular teeth whitening sessions will help and also it would be best to avoid the following:
1) Coffee does have a bad effect on white teeth. Considering the amount of coffee that is consumed on a daily basis there is no doubt that over time coffee will help to diminish the white shade you once had. Coffee will get into the dentine tubes of the teeth and stain intrinsically and extrinsically.
2) Tea: The tannins and acidity of tea will stain white teeth. Constantly drinking these two heavily coloured hot beverages are most peoples downfall.
3) Tomato Sauce: Essentially any substance with a heavy colour can stain your white teeth. Tomato sauce is no exception. Again over time the staining will occur and your white shade will diminish.
4) Red Wine: red wine will stain heavily and it is very acidic too.
5) White Wine: is as acidic as red wine which will affect the enamel of your teeth.
6) Fizzy Drinks: phosphoric and citric aides will destroy the enamel.
It is statistically proven that people with whiter teeth are more confident and smile regularly. It is important to maintain your white shade, avoiding the above foods and drinks will help greatly in maintaining your shade.