The Herbst appliance is specifically designed to aid in correcting Class II malocclusions, and it is effective in restricting maxillary growth mainly by advancing the mandible. Its fixed nature allows it to apply continuous and unidirectional force to the teeth and jaws, which influences growth patterns.
In its functioning, the Herbst works by causing the lower jaw to move forward, which has a direct effect on the position of the maxilla (the upper jaw). The anterior positioning of the mandible creates a functional shift that may lead to restraining maxillary growth as the soft tissue and muscle activities are reoriented based on the new jaw positioning.
The other appliances mentioned, such as the Twin Block, Bionator, and MARA, can also influence jaw relationships, but they typically do not have the same level of significant restriction on maxillary growth as the Herbst appliance. The Twin Block, for instance, allows for some freedom of movement and promotes growth in both jaws, while the Bionator and MARA are more geared towards encouraging the natural growth of the mandible without strong restrictions on maxillary development.
This clear differentiation in mechanism and outcome illustrates why the Herbst appliance is associated with the most restriction of maxillary growth compared to the others