Many of us have experienced tooth sensitivity at one time or another. Tooth sensitivity typically occurs when external stimuli (such as cold drinks or sugary snacks) create a response in the nerve of a tooth/teeth. It creates this response by travelling through the microscopic channels that lead from the outside to the inside of the teeth. The tooth’s outside layer is called the enamel, and the inside layers are called the dentin and pulp. There are various causes why teeth may become sensitive over time.