American Board of Orthodontics (ABO) Practice Exam 2025 - Free Orthodontics Practice Questions and Study Guide

The Twin Block functional appliance is known for exhibiting the worst control of lower incisor proclination among the options provided. Its design primarily serves to advance the mandible and create a more favorable skeletal relationship in patients with Class II malocclusions. However, this appliance often does not adequately restrict the proclination of the lower incisors during treatment.

The Twin Block's mechanism relies on the patient’s bite and muscular function to position the mandible forward, which can inadvertently lead to the tipping of the lower incisors. This proclination effect results from the appliance's design and the forces exerted during function, making it less effective at maintaining the position of the lower incisors compared to other appliances, such as the Herbst, Bionator, or MARA, which generally provide better control over lower incisor positioning due to their structural or functional design.

Other appliances in the options typically incorporate features that counteract lower incisor proclination more effectively. For instance, the Herbst appliance is fixed and functions to maintain mandibular positioning while minimizing movement of the incisors. The Bionator, while also functional, has a different mechanism that can provide better control over the teeth compared to the Twin Block. The MARA device, similar to the Herbst, is