A passive removable or fixed appliance used to prevent closure of a space into which a tooth is expected to erupt, usually following the extraction or premature loss of a tooth. There are a number of designs of fixed space maintainers. See Nance appliance. The unilateral band and loop or crown and loop space maintainer has a band or crown cemented onto the tooth adjacent to the space; a stainless steel wire loop attached to the band or crown extends into the space and touches the tooth on the other side of the space to hold both teeth in place. The bilateral lingual or palatal arch space maintainer usually consists of metal bands cemented on to the molar teeth on both sides of the arch distal to the spaces connected by a stainless steel wire behind the incisors.