Right after it happens
Rinse your mouth gently with warm water to clear any debris, and if you can find the broken piece, keep it moist (in milk or wrapped in a damp cloth) — a dentist can sometimes reattach it. Apply a cold compress to the outside of your cheek if there's swelling, and use gauze to control any bleeding.
How urgent is it, really?
A small chip with no pain can usually wait for the next available appointment. A break that exposes the inner (sensitive) part of the tooth, causes ongoing pain, or leaves a sharp edge cutting your tongue or cheek is worth same-day attention.
What repair typically looks like
Minor chips are often fixed the same visit with bonding — a tooth-colored resin shaped and hardened in place. Larger breaks may need a crown, and if the tooth's nerve is affected, a root canal first. The dentist will confirm the right approach after an exam, sometimes with an X-ray.
In the meantime
Stick to soft foods, chew on the other side, and avoid very hot or cold food and drinks on the affected tooth until you're seen.