Space maintainers are preventive orthodontic appliances used to preserve the space left by premature loss of primary teeth. They help to prevent undesirable tooth movement, such as drifting or tipping of adjacent teeth, which could lead to crowding or malocclusion in the permanent dentition. By maintaining the arch length, they facilitate the proper eruption of permanent teeth and reduce the need for more complex orthodontic interventions later. Unlike other options, space maintainers do not actively move teeth but serve to prevent potential orthodontic problems.

Reference: Proffit, Contemporary Orthodontics, 6th Edition.