The aim of the study is to compare the skeletal and dental maxillary expansion obtained with an Hyrax tooth-borne expander anchored either on the 2nd deciduous molars (V) or on the 1st permanent molars (6).~The main objective is to compare at the skeletal level the distance between the cephalometric points, right jugal (RJ) and left jugal (JR) (maxillary base).~The secondaries objectives are performed at the dental level by measuring the distance between the maxillary first molars mesio-palatal cusp and the cuspids cups. Molar derotation is also assessed
The aim of the study is to compare the skeletal and dental maxillary expansion obtained with an Hyrax tooth-borne expander anchored either on the 2nd deciduous molars (V) or on the 1st permanent molars (6)