Increased sensitivity can be the result of trauma to the teeth or gum disease. When a hot or cold sensation comes in contact with the dentin that is connected to the root of the tooth it causes pain. The dentin is exposed to this contact if its outer coverings the enamel and the cementum are invaded by tooth decay.
Gum disease causes the gum tissue to pull away from the teeth. When this happens the dentin is exposed to cavity causing plaque.
Acid reflux and bulimia are both conditions that can allow stomach acids to get into the mouth and begin to erode the outer layers of the teeth.
Broken teeth or gum disease can both cause sensitivity which will cause pain when the teeth are exposed to hot food or drinks or even a rush of cold air.
Your dentist will want to discuss your symptoms and follow that up with an examination of your teeth and gums. He will take xrays for further evaluation.
Treatments vary from prescription toothpastes and fluoride treatment to fillings and crowns.
Using a toothpaste that is advertised to help relieve sensitivity is a good preventative measure.