Space maintenance is best achieved by preserving the primary molars until they are lost naturally. Sometimes, when a tooth is not able to be restored (have a filling placed) or is infected, the tooth must be extracted. At this point a space maintainer is placed. The purpose of a space maintainer is to hold the space for the permanent tooth to come in. If a space maintainer is not placed after a baby tooth is extracted the teeth beside the space will drift, blocking off the space for the permanent tooth to come in. Once the permanent tooth comes into the mouth the space maintainer will be removed.