Maxillary transverse deficiency is an orthodontic anomaly characterized by the upper and lower dental arches being incompatible due to insufficient width of the maxilla. This condition typically manifests with clinical symptoms such as crossbite, crowding of teeth, and impaired respiratory function. Genetic factors, early primary tooth loss, mouth breathing, thumb sucking, and abnormal swallowing are among the causes of maxillary narrowing. Treatment options vary depending on the patient's age and the degree of suture closure. In pediatric and adolescent patients, rapid (RPE) or slow (SPE) orthodontic expansion can be achieved with palatal expansion appliances. However, in adult patients, due to the less flexible bone structure of the maxilla, methods such as surgically assisted expansion (SARME) or mini-screw-assisted expansion (MARPE) are preferred. Recent studies have shown that MARPE can be effective as a non-surgical alternative in young adults and can provide direct skeletal expansion without damaging the teeth.

Thirty patients with maxillary transverse narrowing will be divided into two groups, MARPE and SARME, based on the amount of expansion required and suture ossification. Hybrid appliances will be custom-made for 15 patients undergoing mini-screw-supported rapid maxillary expansion. The position and number of screws will be determined individually for each patient. The screws to be used will have a diameter of 2 mm and a length of 14 mm. The screws will be placed under local anesthesia. A minimum of 2 and a maximum of 4 screws will be applied to patients. In the group undergoing surgical-assisted rapid maxillary expansion, expansion will be applied using an acrylic cap splint. In the SARME group, patients will undergo a standard Le Fort 1 osteotomy under general anesthesia. The appliances in both groups will be removed after a 6-month retention period. Cone beam computed tomography (90 kVp; 10 mA; 200 mm Voxel Size) will be taken from patients in both groups before starting the expansion treatment (T0) and after the 6-month retention period. Measurements will be performed on these radiological images using the Planmeca Romexis program. The volume, anteroposterior diameter, transverse diameter, length, and angle of the nasolacrimal canal and nasopalatine canal will be measured before and after treatment. The volume of the maxillary sinus and the diameter of the ostium openings will be measured. The nasal breathing volume and septal deviation will be measured on CBCT before treatment (T0) and at the end of the retention period (T1), and the results will be compared.

Inclusion Criteria:

• Diagnosis of maxillary transverse deficiency.
• Patients aged 15 years and older.
• Presence of unilateral or bilateral crossbite.

Exclusion Criteria:

• Severe facial deformities or craniofacial syndromes.
• History of previous orthodontic treatment.
• Existing pathology or history of surgery related to the paranasal sinuses, nasolacrimal system, or orbital cavity.
• Inadequate patient cooperation.
• History of trauma, or previous maxillofacial/plastic surgery procedures.
• Clinical signs or symptoms of maxillary sinus pathology (e.g., maxillary sinus cysts, sinusitis).