What kinds of food should you eat to have strong and healthy teeth?

Crunchy foods which are low in sugar and not too acidic. E.g, carrot sticks and most salad ingredients. Things which you have to chew (e.g crusty bread). Dairy foods are also useful for overall bone health, particularly if you're young and your adult teeth are still forming.

(Clearly, if you just ate those things it would not constitute a healthy diet. You should, of course, eat a healthy diet including protein and carbohydrates, however most proteins/carbohydrates are not beneficial to teeth, so I did not list them. )

However, the thing which makes the biggest difference to dental health is good dental hygiene. Brush regularly, with an electric toothbrush if you can. (Even cheap electric toothbrushes are better at cleaning then manual). Make sure you brush before going to sleep. Mouthwash is also useful; bear in mind that you do not need to use one of the slightly disgusting tasting mouthwashes for it to be effective.