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 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

Inclusion Criteria:

• Patient coming to the dental clinic for a first orthodontic consultation in mixed dentition
• Patient aged 6 to 12 years
• Patient with a transverse maxillary deficiency requiring rapid maxillary expansion
• Presence of 1st permanent molars "6" and 2nd deciduous "V" molars with sufficient root length

Exclusion Criteria:

• Syndromic patients (all syndromes combined: cleft lip, etc.)
• Patient with V or 6 with decays (or with major root resorption)
• Patient with oral hygiene non compatible with orthodontic treatment
• Failure to obtain informed written consent
• No affiliation to a French national medical health system
• Patient with a legal protection measure