A pulpotomy, also known as a baby tooth root canal, is the removal of a portion of the pulp, due to decay that has reached the nerve/pulp of the baby tooth.
Like adult root canals, the dentist will access the nerve chamber of the tooth, and remove some of the nerve/pulp of the tooth. Unlike adult root canals, this is a very short procedure, as only part of the pulp needs to be removed, and does not require the time consuming filing of adult root canals.
Advantages of a pulpotomy are if the tooth has been symptomatic, this procedure will likely alleviate the pain, in addition to allowing for the tooth to be preserved until it is ready to fall out naturally.
There is little disadvantage to a pulpotomy. Pulpotomies have a 90% success rate. Occasionally, the nerve of the tooth is so badly damaged that it does not respond to pulp therapy, resulting in the need for extraction of the offending tooth. Certain circumstances increase the likelihood of failure with pulpotomies, your dentist will discuss your child's situation with you during diagnosis.
The only alternative to a pulpotomy is extraction, and placement of a space maintainer. However, if it is possible to save the baby tooth, this is the best alternative because it preserves the appropriate spacing for the adult dentition.