Ice, because it is so hard, can overload the teeth's ability to withstand the force of chewing it. It can cause small micro fractures in the teeth. Micro fractures are thin cracks that can run from the chewing surfaces all the way down to the root surfaces. Micro fractures can weaken the teeth and make them more likely to break. They can also cause the teeth to be extremely sensitive.
Please don't risk it. Try sucking on the ice cubes instead of chewing them.
- from Susan B. (Dental Hygienist)