Young children with backward positioned lower jaw/chin will be recruited to have an upper jaw expansion appliance. Previous research showed that the use of similar appliances can lead to lower jaw forward growth. 60 young children aged 9-11 will be recruited to have either active or non-active Wilson type upper arch expansion appliance. Patients will have special x-ray (Cone Beam computed tomography) before and after treatment (after 9 months) of starting the treatment. After participation, routine orthodontic treatment will be continued.

Previous research showed that the use of upper jaw expansion appliances can lead to lower jaw forward growth (1). 60 young children aged 9-11 with backward positioned lower jaw/chin will be recruited to have either active or non-active Wilson type upper arch expansion appliance. Patients will have special x-ray (Cone Beam computed tomography) before and after treatment (after 9 months) of starting the treatment. After participation, routine orthodontic treatment will be continued.

Inclusion Criteria:

1. Class II skeletal due to lower jaw backward projection
2. Class II malocclusion
3. Early mixed dentition (all first permanent molars erupted, as well as all erupting upper and lower permanent incisors)

Exclusion Criteria:

1. Other orthodontic treatment provided
2. Growth problems (craniofacial syndromes, etc.)