Contemporary Ortho Appliances Practice Test

Twin block is a functional appliance designed to posture the mandible forward in growing patients with class II malocclusion. When the patient bites, the upper and lower bite blocks interlock and guide the lower jaw forward, creating anterior-directed forces through the dentition. This forward push makes the mandible translate toward the front, which is the primary way the appliance corrects the skeletal relationship. Vertical components of contact can occur as the bite closes, but they are not the main mechanism; the essential effect is forward displacement of the jaw. That’s why the correct direction is forward.