This is the final and probably most effective advancement on the numerous double plates. In principle, these are offset activators split into two parts for the upper jaw and two parts for the lower jaw. Just like the double plate braces, they bring the lower jaw as far forward as possible in order to treat an Angle-Class 2 distoclusion. In order to do this, the double plates are conveniently joined together by a mechanical element. These are usually rigid metal lugs like on the Müller-Dornen or the more recent forward-pressure double plates. Whereas on the Twinblock there are plastic strips located between the teeth. The advantage of the forward-acting double plates is that they do not impede speech quite so much because they take up less space and they can also hold the lower jaw forward, even when the mouth is slightly open With mono-blocks such as the Activator and Bionator, etc the lower jaw quickly sags backwards when the mouth is slightly open which means that it loses its effect.

In the case of the Twinblock, the interlocking elements that form part of the plastic body of the appliance are positioned between the rows of teeth where they create a jagged line. The Twinblock is essentially an appliance that is designed to be worn all day – apart from when eating and cleaning the teeth – and can often be worn for several weeks at a time. When a child needing treatment actually wears the appliance, the Twinblock is almost as effective as the Herbst-Scharnier. Unfortunately, 30% – 50% of children do not wear this appliance as directed so, in everyday life, the Twinblock is not nearly as effective as the fixed Herbst–type appliances. In spite of this, the Twinblock belongs to a small number of removable braces that can be used with a clear conscience today.