A sure sign. If there are particular times when you bite into a tooth and their is an instant sharp pain upon biting or letting go, and then the pain is gone just that quickly as well, then you have a cracked tooth pretty much for sure. It can be sensitive to sweets and cold as well. But the biting thing is the important finding here. These teeth are recommended for crowns. If a crown is present, a root canal.
Cracked tooth. Unlike teeth with obvious fractures, teeth with cracked tooth syndrome usually have fractures that are too small to be detected on X-rays and very difficult diagnose. Sometimes the fracture is below the gum line in the root area, making it even more difficult to identify. Your dentist may use special tools to test the tooth and diagnose cracked tooth syndrome.
Dental evaluation. See your dentist who can clinically examine you, check with x-rays or other diagnostic images such as 3d cbct technology if necessary, and perform other diagnostic tests.
Go to a dentist. Fractures and microfractures / craze lines may or may not be visible to the untrained human eye. Your eyes can not see what your mind can not think. Your dentist has a microillumiating devices and other techniques and test to check if the tooth is cracked or not.