Fixed orthodontic appliances are characterized by which type of action?

• A. Functional action
• B. Combined action
• C. Mechanical action
• D. Apparatus with the occlusal overlap

Answer: (C)

Fixed orthodontic appliances move teeth through mechanical forces generated by the bracket–wire–ligation system. Brackets bonded to teeth hold an archwire in slots; when the wire is bent, adjusted, or ligated, it exerts controlled forces and moments on each tooth. Those forces drive tooth movement through the surrounding bone, producing tipping, translation, rotation, or root movement as bone remodeling occurs over time. This reliance on physical force transmission and controlled moments is what defines their action as mechanical, not functional jaw muscle activity or growth modification. Functional action would describe appliances that alter jaw function or growth, while the option about occlusal overlap doesn’t address how the appliance works.