Twin block braces are commonly used to correct an overjet (the space between your top and bottom teeth when your mouth is closed) A twin block brace would promote the closure of this gap. Working on similar prinicples to the removable appliance, the twin block appliance works by preventing your mouth from closing unless your jaw is in the correct position. Once your mouth is closed in the correct position, the blocks which are located at the back of the mouth, prevent you from returning to the previous incorrect position.
Twin block braces can only be worn at a certain age. The growth of the jaw bone is manipulated by the appliance to correct the bite. Twin blocks correct the wearers bite and also the facial profile. Twin block braces can be quite uncomfortable, and the wearer may experience aching the the jaw joint.