Why does sugar cause pain when it comes in contact with a tooth cavity?

Dr. Sachin Seth, an associate professor in the Faculty of Dentistry at Dalhousie University in Halifax, says that the pain associated with sugar begins when the tooth's outer shell, the enamel, is worn thin. Sensitivity to sugar, or even hot and cold beverages, starts when the root surface no longer has an enamel covering.

Exposed nerves in the underlying part of the tooth, called the dentin, relay sensations into the nerve centre of the tooth, called the pulp. Sugars, hot and cold sensations, and even salt stimulates these nerve fibres and causes the sensation of tooth pain.

What sets sugar apart, though, is that it's a food source for the bacteria in our mouths. The bacteria metabolize the sugars and create acids, which adds to the pain in our cavities.