Using your teeth as tools is tempting sometimes, but it causes damage that you can’t see right away. When you chew on ice, you are causing extreme temperature and pressure changes, thus creating micro-cracks in your tooth enamel. It can chip your teeth, as well as cause gum injury, too. If you have sensitive teeth, chewing ice will most likely worsen the pain rather than numb it.
If you are tempted to chew ice, try chewing sugarless gum instead. If you want the crunch, you could try carrot sticks, celery, or apples. Your teeth will thank you later.