The correct answer is Space gainer because it is a corrective, not preventive, orthodontic procedure. Preventive orthodontics aims to preserve existing space and guide proper eruption to avoid malocclusion, as seen with space maintainers, oral hygiene instructions, and fluoride application. In contrast, space gainers are used to regain lost space after premature tooth loss or crowding has occurred, thus functioning as an interceptive or corrective measure rather than purely preventive.

Reference: Contemporary Orthodontics, 6th Edition.