If the patient fulfill the inclusion criteria, they will be asked to participate in the study. After being informed about the study and the planned treatment, participants and their guardians will give their written consent to participate in the study.~Therafter they will be consecutively randomized into one of two groups with different control intervals, Group 1 (every 4th week) and Group 2 (every 6th week). They will recieve a clinical and radiological examination and then start treatment with a Twin Block appliance.~The Twin Block appliance will be fitted with a digital timer module to measure the wear time of the appliance objectively.
To compare the effect of two control intervals (once every 4th week or once every 6th week) on the wear time of a Twin Block removable appliance.