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

The Twin Block functional appliance typically exhibits the least favorable proclination control of the lower incisors compared to the other options. This appliance is designed to encourage forward growth of the mandible by harnessing the natural bite forces during function. Due to its design, the Twin Block often leads to more significant proclination of the lower incisors, especially as the patient interacts with the appliance during normal functioning.

In contrast, appliances like the Herbst and MARA are primarily fixed functional appliances that do not allow for as much anterior movement of the lower incisors. They engage the molars effectively and help maintain a more neutral position of the anterior teeth. The Bionator, while more flexible than the Herbst or MARA, still tends to provide better control over the proclination of the lower incisors compared to the effects seen with the Twin Block.

Thus, the nature of the Twin Block's function in promoting forward jaw positioning while allowing greater freedom of movement tends to lead to less control over the anterior inclination of the lower incisors. This makes it the least favorable option for proclination control in this scenario.