Yes, sweets and foods with acid, like candy and soda, could stick to teeth and lead to cavities. Smoking and chewing tobacco can cause oral cancer and gum disease.
While teeth are strong enough to chew ice and tear open packages, this can break them and stress your jaws. Gritting or grinding down on teeth when you're stressed may crack them.
Biting your nails is another bad habit. It pulls your jaw out of position and changes how your teeth fit together.