The Haas appliance is a tooth-borne tissue-activated/acrylic alternative to the Hyrax appliance. Studies have indicated the Haas appliance with palatal acrylic will reduce the tipping effect on the teeth and provide a larger sutural displacement when used as a rapid expander, compared to the Hyrax. Optional acrylic is used on the occlusal with banded versions (shown below) to provide easy checks for leakage.