Which of the following is an example of an orthodontic force generator?

An orthodontic force generator is a device designed to apply specific forces on the teeth to achieve desired movement and alignment during orthodontic treatment. Headgear is a crucial example of an orthodontic force generator because it is specifically engineered to exert controlled forces on the teeth and jaws, facilitating correction of dental and skeletal discrepancies. This device typically consists of a framework that attaches to the child's head or neck and is connected to the braces on the teeth. By providing anchorage away from the teeth, headgear can target specific areas, allowing for effective molar retraction or maintaining a proper bite relationship.

Other options, while related to orthodontic treatment, do not serve as active force generators. A retainer's primary role is to stabilize teeth post-treatment, providing passive holding rather than generating forces. Invisalign is a form of clear aligners that exerts gentle pressure on teeth to promote movement, but it does so through a different mechanism than traditional force generators like headgear. A bonding agent is used in the process of adhesion for brackets and other orthodontic appliances but does not generate any forces itself. The unique capability of headgear to create the necessary forces for orthodontic adjustments makes it the most suitable example of an orthodontic force generator.