"Tooth Sensitivity" is Caused by the Exposure of Dentine Tooth sensitivity is caused by the gradual exposure of the softer part of your tooth that lies under the tooth enamel, called "dentine". Dentine has tiny tubes ('tubules') that contain nerve endings and are filled with fluid. Eating or drinking foods and drinks that are hot, cold or sweet can cause this fluid to move.
When you crack your tooth you need to show it to a dentist. A crack can allow bacteria to penetrate through the protective enamel and dentin directly into the pulp cavity where an infection can begin and abscess. This can lead to the tooth needing a root canal (endodontic therapy) or removed (extracted).