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Sometimes the dentist is able to reattach the portion of tooth that broke off, so you should save it if you can. Take the shard and put it in a container with milk or saliva to keep it from rotting. Then bring it with you when you visit the dentist. You should never try to reattach the portion of tooth yourself. Not only will this not work without proper equipment, but you'll cause severe pain for yourself if you poke an exposed nerve. Your mouth is full of bacteria, and any injuries can get infected easily. To help stave off infection, rinse your mouth with a salt water solution when you know you've broken a tooth.  Mix 1 tsp of salt into 1 cup of warm water. Swish the mixture around your mouth for 30 to 60 seconds.Concentrate on the injured area. Be sure not to swallow any of the mixture. Repeat this rinse after meals. If you've damaged your tooth badly, the pain can be severe. You can treat it with OTC pain relievers until you go to the dentist and get it fixed. Ibuprofen products like Motrin and Advil are usually preferred over acetaminophen because ibuprofen also reduces swelling in addition to treating pain. But if ibuprofen isn't available, take an acetaminophen product like Tylenol. Sometimes a chip in the tooth will produce a jagged edge that could cut your tongue or gums. To prevent damage to your mouth, cover the edge with dental wax. You an purchase this in the oral care aisle of most pharmacies. Alternatively, you could also cover the edge with a piece of sugar-free chewing gum. It's possible that you won't be able to see your dentist for several days after you crack your tooth. In this case, you'll have to eat before your appointment. Take the following measures to reduce pain and prevent further damage when eating.  Stick with soft foods. The cracked tooth is weakened and susceptible to further damage. Hard foods could make the crack worse and cause pain. Opt for soft foods like pudding, soup, and oatmeal until your doctor performs the necessary work. Don't eat anything especially hot or cold. The cracked tooth will be sensitive to extreme temperatures, and very cold or hot foods can cause pain. Serve food at room temperature to avoid any problems. Try to eat on the unaffected side of your mouth. Any chewing can cause pain and further damage, so if possible you should avoid chewing with the cracked tooth.

Summary:
Save the shard of tooth if you have it. Rinse your mouth with salt water. Take over the counter pain relievers to help with the pain. Cover sharp edges with dental wax. Be careful when eating until you see your dentist.