The investigators will perform a prospective, non-randomized observational study. The aim of this study is to evaluate stability of tooth-borne, bone-borne and hybrid expansion following SARPE by using data collected according to the existing SARPE follow-up protocol. The insights of this study might elucidate the preferred expansion technique and improve surgical technique.

Maxillary transverse discrepancy (MTD) is a difficult deformity to correct. In skeletal immature patients, an orthopedic-orthodontic expansion is the preferred treatment strategy. In case of a skeletal mature patient, a surgical treatment should be considered. A Surgically assisted Rapid Palatal Expansion (SARPE) procedure is a common surgical treatment for MTD in skeletal mature patients. In this procedure the skeletally mature, maxillary sutures are surgically reopened. One week postoperatively, the patient will activate the expander appliance. There are three widely-used expander appliances: tooth-borne, bone-borne and hybrid expanders. The use of the expander appliance is based on surgeon and referring orthodontist's common practice and preference. A tooth-borne expander is an appliance which is supported by the teeth and bridges the palate. A bone-borne expander is surgically placed at the level of the palate during SARPE surgery. Hybrid expansion is a combination of tooth-borne and bone-borne expansion. These appliances progressively widen the maxilla by daily activation of the distractor. The activation is stopped when the surgeon and/or referring orthodontist judge that the maxilla is sufficiently expanded. However, historical research with the use of cast model's and 2D posteroanterior cephalograms suggest that this expansion is not stable. With the emergence of 3D Cone-Beam Computed Tomography (CBCT) and its appliance as standard of care for pre-operative diagnosis and postoperative follow-up, stability and complications can be assessed more accurately. The goal of this study is to prospectively evaluate stability following SARPE, by analyzing the clinical and radiological data collected according to the existing clinical SARPE follow-up protocol. The secondary outcome is to evaluate complications following the three distractors.

Inclusion Criteria:

• Maxillary transverse discrepancy
• Skeletal mature patients
• SARPE treatment is indicated

Exclusion Criteria:

• Patients with a syndrome with an influence on head-and-neck morphology (such as Apert, Crouzon syndrome)
• Cleft patients

Patients undergoing SARPE surgery due to maxillary transverse discrepancy

On request