When tooth decay infects deeper into a tooth, it can reach the pulp of the tooth. The pulp is the center of the tooth and it contains nerves and blood, which provide nutrition and sensory feeling for the tooth. Decay reaching the pulp leaves an open channel to the nerve. So when food, drinks, and even air hit the tooth, the nerve is being directly stimulated. This is why deep cavities can hurt so much.
Once bacteria reach the pulp of a tooth, there's no way of cleaning it out and patching up the tooth leaving the pulp intact. A pulpotomy is the process of cleaning out the contents of the pulp and replacing it with a filling. So a pulpotomy is like a root canal for baby teeth. The tooth should then have a cap (hyperlink) placed on it and after a day or two, that tooth will have lost all sensation but will act and function like a normal tooth.
Teeth that require a pulpotomy can be diagnosed either by looking in the child's mouth or by looking at the X-rays. A diagnosis is usually confirmed by doing both. If your child is complaining of persistent and lingering pain, a pulpotomy may be the preferred treatment method. Sometimes antibiotics are prescribed in addition to clear up any infection.