Which of the following is an example of a fixed orthodontic appliance?

Braces are considered a fixed orthodontic appliance because they are permanently attached to the teeth for the duration of the treatment. This system involves brackets bonded to the teeth and connected by wires, which work together to gradually move the teeth into the desired position.

On the other hand, retainers, aligners, and space maintainers are not classified as fixed appliances. Retainers are typically removable devices used after orthodontic treatment to maintain the new position of teeth. Aligners, such as Invisalign, are also removable and rely on a series of clear trays created specifically to shift teeth gradually. Space maintainers, while they may be fixed to hold space for permanent teeth in children, do not serve the same function as braces, which focus on actively moving teeth into alignment.

Thus, braces are uniquely identified as a fixed appliance because of their attachment and role in actively adjusting teeth.