Aim of the study: To evaluate 3-Dimensionally the effects of myofunctional trainers in treatment of Class II malocclusion with anterior open bite in a sample of Egyptian children during mixed dentition stage.Materials and methods: 10 growing female patients with an age range of 8-11 years having skeletal Class II malocclusion with anterior open bite used the myofunctional trainer for a 6- months evaluation period. Cone beam computed tomography scan (CBCT) images were taken before and after the evaluation period to assess the skeletal and dental changes in the 3 planes of space.Results: After the 6-months evaluation period, the results showed a significant increase in mandibular length post-treatment in the sagittal plane. While in the coronal plane, there was a significant increase in maxillary width and mandibular width post-treatment. In axial plane, significant increase in the mandibular arch depth post-treatment was reported.Conclusion: Myobrace®, a prefabricated functional appliance, could be used in treatment of patients with skeletal Class II deficient mandible not associated with anterior open bite.