An in vivo study evaluating the efficacy of the Tandem appliance in the treatment of maxillary deficiency in growing patients compared to the conventional facemask appliance treatment. Pre-treatment and post-treatment lateral cephalograms will be taken. Dentofacial, sagittal and vertical skeletal measurements will be taken at three assessment times. Changes within each group will be assessed. In addition, the changes between the two groups will be compared.