Final answer:
Space maintainers are dental devices designed to keep the space open when a primary tooth is lost prematurely, ensuring permanent teeth can erupt properly and maintain alignment.
Step-by-step explanation:
The correct option for devices designed to hold open space when a primary tooth has been lost prematurely is a) Space maintainers. Space maintainers are dental devices used specifically for this purpose. They come in different forms, but all are designed to maintain the space where a tooth has been lost, allowing the permanent tooth to erupt properly in its place. This is important because losing a primary (baby) tooth too early without a space maintainer can lead to space loss and subsequent misalignment of the permanent teeth. This is particularly critical for maintaining proper alignment for permanent molars, which, along with incisors, canines, and premolars, are part of the 32 permanent teeth that replace deciduous teeth.