A space maintainer is an appliance that is custom-made by a dentist or orthodontist in acrylic or metal material. It can be either removable or cemented in a child's mouth. Its purpose is to keep the space open to allow the permanent tooth to erupt and come into place. When should space maintainer be removed? A dental space maintainer should be removed when the permanent tooth is ready to erupt. Your dentist will know when this is about to happen because he or she will be taking regular x-rays of your child's mouth after installing the space maintainer.