To maintain the space of a second primary molar, the appliance used is?

The correct answer is a space maintainer. This device is specifically designed to preserve the space left by a primary tooth after it has been extracted or has fallen out prematurely. Maintaining the proper spacing is crucial because it prevents the adjacent teeth from drifting into the gap, which can lead to misalignment and complicate future orthodontic treatment.

Space maintainers can be either fixed or removable, with the fixed variety being more commonly used in pediatric dentistry for situations involving molars. They help ensure that the permanent teeth have adequate space to erupt properly, supporting overall dental arch development.

The other options do not fulfill the specific purpose of maintaining space after the loss of a primary molar. A retainer is primarily used after orthodontic treatment to keep teeth in their new positions. An orthodontic band is a component used in braces but does not function to maintain space on its own. A bridge is a restoration used to replace missing teeth in adults, requiring the presence of adjacent teeth for support, making it unsuitable as a space maintainer in the context of primary teeth.