This study was accomplished to determine the 'postural adaptations of the structures related to cervical vertebrae, after changing the functional conditions with the activator. For this reason 10 individuals with Angle class II / 1 malocclusion, who could be treated with an activator were chosen. Before and half an hour after the application of the activator, lateral cephalometric radiographs were obtained in natural head posture. According to the cephalometric evaluations we observed that with the extension of the head, the hyoid bone moved upwards. We also discussed the relationships between the head posture, hyoid bone position and pharingeal airway dimensions.

Keywords: Activator, Head posture, Extension, Hyoid bone position, Pharingeal air-way