Current designs of activators impede eruption of the upper posterior teeth while allowing the lower incisors to erupt.

• A. Upper posterior teeth; lower incisors
• B. Lower posterior teeth; upper incisors
• C. Both; None
• D. Neither

Answer: (A)

Functional activators modify eruption patterns by controlling how the bite is set and how the jaws relate when the appliance is worn. In current activator designs, an upper bite plane or ramps create a vertical stop that interacts with the lower teeth as the mandible is advanced forward. This arrangement discludes the upper posterior teeth from seating fully into their occlusal surfaces, which tends to slow or impede their eruption. At the same time, the forward posture and the way the appliance guides the anterior teeth allow the lower incisors to erupt and adapt to the new position, maintaining space and incisal contact. So, the design favors eruption of the lower incisors while restraining eruption of the upper posterior teeth.