Teeth can be sensitive due to a variety of reasons but most of the time it is usually due to an irritation to the nerve of the tooth. A tooth or teeth that are sensitive can alert you to a problem that is going on and it is important to have it checked at your dentist.
When teeth are or become sensitive it means that the pulp-the inner portion of the tooth where the nerve is-has been stimulated/excited by something.
In the case of dental decay, the nerve may become irritated or inflamed due to bacteria. When a cavity initially forms it usually starts in either the enamel, when it travels through the enamel it meets the dentin and ultimately the pulp. When the pulp has become irritated due to bacteria a person may be sensitive to cold, hot, sweet or biting force.
Teeth can also be sensitive due recession which exposes the root of the tooth. The root of the tooth is made of soft cementum and is not made to be exposed to the oral cavity. The root is much more susceptible to cavities; as well it contains small tubules which run perpendicular to the pulp of the tooth. Each time someone consumes something cold, occasionally hot or sweet this causes the tubule to constrict and it puts pressure on the pulp. This constriction makes the tooth sensitive.
In the case of dental decay, sometimes a sedative otherwise known as a temporary filling may work to calm the nerve and allow the dentist to apply a filling at a later date. If the nerve of the tooth becomes irreversibly irritated then a root canal to remove the pulp and nerve may be necessary.
If the root of the tooth is exposed due to recession, two options exist for coverage to protect the soft root surface. At times a white filling may be an option to cover an exposed root to prevent sensitivity though it is not an optimal one as long term stability on the tooth can be poor. The gold standard to cover an exposed root is gum grafting. Gum grafting can either be done with the patient’s own tissue which is taken from the palate or with a dermal matrix such as alloderm.