Summarize:

If you crack your tooth severely enough, you'll probably feel significant pain right after the injury. If you experience this, examine the tooth that hurts and see if there is a piece missing. If so, you've indeed cracked a tooth. Also keep in mind that you may still have a shard of tooth in your mouth. This can cut you if swallowed, so try to spit it out if it's still in your mouth. Save the shard if you have it. If your crack is less severe, you may not feel immediate pain. Instead, you'll probably experience a more dull pain that comes and goes. Often your tooth will hurt when you're chewing or when you eat very hot or cold foods. If you experience this kind of pain, it would be a good idea to investigate further. If you suspect that you may have cracked a tooth, a visible inspection should help confirm your suspicions. Look for a visible crack or missing section of your tooth. You might also be able to feel the cracked tooth if you can't see far enough into your mouth. Try carefully rubbing your tongue around your teeth. If you encounter a rough or pointy section, this would indicate a crack. If you have trouble finding the crack, you can also look at your gums. The gum line around a cracked tooth may swell and turn red. Look for this symptom to help locate your cracked tooth. Whether you know for sure you cracked your tooth, or are just having pain and can't locate it, visit your dentist as soon as possible. Cracked teeth are treatable, but it is important to visit the dentist as soon as possible to prevent further damage. In the meantime, there are a number of steps you can take to protect your mouth and alleviate your pain.
Look for a sudden pain right after impact or chewing something hard. Note erratic pain in your tooth. Examine your tooth for visible cracks or damage. Look for swelling or inflammation around the cracked tooth. Schedule an appointment with a dentist.