In this research 22 subjects of 8–12 years old, who had posterior cross bite relationships accompanied by high-arched palate, were choosen and they were divided in two groups. In the investigation group, while rapid maxillary expansion has been applied with Haas appliance modified with occlusal bite planes to 12 subjects, in the control group Haas appliance has been used only. Dental and skeletal changes resulting from the rapid maxillary expansion, are evaluated in a comparative study of the frontal and lateral cephalometric x-ray films and dental casts. It has been found that while rapid maxillary expansion produces dental and skeletal expansion, the bite planes added to the appliance prevents the open-bite in a great measure. In addition, it caused less vestibular inclination of the first upper molars.

Keywords: Occlusal bite plane, Haas appliance, Rapid Maxillary expansion