The tooth is made up of two basic parts: the crown and the root. The crown is the part that is visible when you smile, and this part is covered by a hard protective material called enamel. The root houses the nerves of the tooth and is hidden deep within gum tissue and bone. It is not covered by enamel; instead, it is made up of dentin, a yellow bone-like material that contains thousands of tubules that lead to the root’s nerve centre.

Tooth sensitivity occurs when the protective layer of gum tissue and enamel is worn away, exposing the dentin underneath. As such, when cold, hot or sweet materials are ingested, the food can easily come into contact with the nerves through the tubules in the dentin, causing pain.
There are many common practices that can lead to sensitive teeth, and these include:

1. Vigorous brushing. While it may seem like brushing your teeth hard or using a hard-bristled brush will make them cleaner, doing so can actually result in sensitivity. This practice can wear out the enamel layer of the teeth or cause gums to pull away from the root, exposing the sensitive dentin layer below. It’s important to maintain oral hygiene, but try to avoid aggressive brushing. To prevent sensitivity, brush gently and use toothbrushes with softer bristles.
2. Mouthwash use. Over-the-counter mouthwash solutions may indeed help freshen your breath and kill bacteria in the mouth. However, some solutions contain acids which can erode enamel and further expose the sensitive dentin layer of teeth. These acids can also wear away the dentin itself, worsening the condition of your teeth. If you need to use mouthwash regularly, a good alternative is a neutral and acid-free fluoride solution.
3. Teeth whitening. Products that whiten the teeth contain hydrogen peroxide, which can erode the protective enamel layer of the tooth. Other whitening substances, such as baking soda, may be abrasive and also wear away the top layers. Excessive use of tooth whiteners can actually be counterproductive — removing the enamel will expose the naturally yellow dentin underneath.
4. Consumption of acidic food. As mentioned earlier, acid can wear away protective layers. Commonly consumed acidic foods include citrus fruits, pickles, tomatoes, tea and soda. To balance the acidity in these foods, try eating a small piece of cheese or drinking milk after consuming them.
5. Cracked teeth and tooth grinding. Cracks in teeth are prone to plaque and bacteria build-up, which can cause cavities. This exposes the pulp and nerve roots to ingested substances, resulting in pain. Grinding and clenching on teeth, on the other hand, wears away enamel. It’s best to use mouth guards to prevent damage from tooth grinding, while proper hygiene and fillings may be necessary to address chipped or broken teeth.