1. Space maintainers are appliances used to maintain space created by premature tooth loss. They prevent crowding, impaction, and other issues by holding space open.
2. Common space maintainers include band and loop, crown and loop, lingual arch, Nance palatal arch, and removable appliances. The best option depends on factors like time since tooth loss and dental age.
3. Space maintainers are generally indicated when space is closing, future orthodontics may be simplified, or to prevent issues like supraeruption. They are contraindicated if space isn't closing or the succedaneous tooth is absent.