Chewing ice:

It’s natural and sugar free, so you might think ice is harmless. But munching on hard, frozen cubes can chip or even crack your teeth. And if your mindless chomping irritates the soft tissue inside a tooth, regular toothaches may follow. Hot foods and cold foods may trigger quick, sharp jabs of pain or a lingering toothache. Next time you get the urge for ice, chew some sugarless gum instead.

Researchers have found that a single toothbrush can be loaded with as many as 10 million germs and bacteria. In fact, recent studies even found that your toothbrush could be a breeding ground for tiny microorganisms.