Which of the following does not function as a space maintainer?

Lingual arch is the most effective appliance for space maintenance and minor tooth movement in lower arch. Stainless steel crown and class II restorations, maintain the space and prevent supra-eruption and tipping of adjacent teeth. Palatal expander is used for palatal expansion. It can increase the space in the arch, however, it cannot be used as a space maintainer. Textbook of orthodontics, Gowrishankar 2nd edition page 521