This appliance was the first rapid maxillary expander and was popularized by Hass in the 60's. It is constituted by:
1. Cemented bands on the first upper premolars and molars.
2. Palatine connection wires that are soldered to the bands, which can also be extended through the buccal aspects of the premolars and molars, in order to provide stiffness to the appliance.
3. Two acrylic components assented on the palatine vault in contact with the palatal mucosa.
4. An expansion screw imbedded in the acrylic components on the midline of the palate.
Dr. Hass, in his studies, sustains that this appliance produces a bodily movement of the teeth due to the acrylic
support of the appliance, because these forces are not only applied on the teeth, but also on the soft and hard tissues
of the palate.