Did you know that 1 in every 8 Americans (including kids) has sensitive teeth?! Every tooth has nerves at its center. When the tooth is healthy, the nerve is protected by the outer layers. If the tooth enamel is damaged or erodes enough, it can expose the deeper porous dentin layer and subject the nerves to much more input than they are supposed to get. That tends to make temperature changes or even a sudden burst of sour or sweet flavor very uncomfortable or even painful.
Erosion is the main cause of tooth sensitivity but not the only one. Exposed roots can be very sensitive because roots rely on gum tissue to protect them, not enamel. Gum recession can leave roots exposed and vulnerable. Gum recession can be caused by brushing too hard, less than ideal dental bite (malocclusion), loss of bone or periodontal attachment or even the position of the tooth in the jaw bone. Damage to a tooth, whether through an accident or cavities, also leads to dental sensitivity.
There are several things to do for sensitive teeth. First, throw out the hard-bristled toothbrush and get a soft-bristled one. It doesn't take much pressure to clean away plaque when we brush, but too much can scrape away enamel and gum tissue. Switching to a toothpaste formulated for sensitive teeth should also help, and cut back on sugar intake and very acidic foods and drinks. You may also want to consult your dentist and orthodontist to find out if your bite may be contributing to your dental sensitivity.