The Bionator I is a removable functional appliance used to treat patients with a Class II malocclusion and a deep bite. While the appliance holds the mandible in a protruded position with acrylic, there is no coverage of the posterior teeth. Instead there are fluted channels angled facially cut into the acrylic that guide the eruption of posterior teeth. This allows for the correction of a deep bite while also expanding the arches dentally. An acrylic cap covers the mandibular incisors and the maxillary incisors contact this cap on a flat plane. This prevents the undesirable eruption of the anterior teeth while also controlling flaring of the mandibular incisors which can occur as a result of the forces exerted on the mandible. There is no acrylic in the palatal vault to allow the proper positioning of the tongue. An omega loop coffin spring joins the two halves across the palate for rigidity and can be activated for lateral expansion of the appliance if an optional expansion screw located on the midline lingual to the lower anteriors is utilized.