Space maintainers help "hold space" for permanent teeth. This is done with a combination of bands and wires designed to hold the remaining teeth in a position that will allow for future permanent teeth to erupt in the proper location.
Your child may need one if he or she loses a baby tooth prematurely, before the permanent tooth is ready to erupt. If a primary tooth is lost too early, adult teeth can erupt into the empty space instead of where they should be. When more adult teeth are ready to come into the mouth, there may not be enough room for them because of the lost space. To prevent this from happening, the dentist may recommend a space maintainer to hold open the space left by the missing tooth.
The advantage to using a space maintainer is it will minimize orthodontic problems caused by premature loss of a baby tooth and the need for orthodontic remedies.
The disadvantage is your child will need to wear the appliance until the permanent tooth erupts. If not kept clean, decay can occur under the bands.