A child may loose a baby tooth prematurely (i.e. before it was supposed to fall out naturally). The reason for this is usually the dentist removes it because it is decayed or there is an abscess.
This early loss of a baby tooth may cause problems with the development of the permanent dentition.
The space in the dental arch for the successive permanent tooth may be lost causing a permanent tooth to become impacted.
The centreline of the permanent teeth may shift to the left or right side depending on which side the baby tooth was lost early.
To prevent the development of these problems sometimes a space-maintainer is fitted. There are a number of different designs of space maintainers to suit different situations. They may be fixed or removable.