Cracked Tooth Syndrome
Teeth with large fillings (and/or root fillings) are weak, and can break when you bite. They sometimes can have hidden cracks which make them tender to bite on or sensitive to hot or cold. The molar and premolar teeth are most commonly the teeth affected.
The reason it hurts to bite when you have a cracked tooth is that your tooth is flexing which stimulates the nerve in the tooth. Bacteria and toxins can enter the pulp (nerve) through the crack. This causes the pulp to become inflamed and sensitive.
Early detection and treatment is important as developing cracks can be slowed down or stopped, increasing the chances that the tooth can be saved. The treatment required depends on the extent and position of the crack.