The goal of this randomized clinical trial is to compare distalization of maxillary first and second molars achieved with a device supported with mini screw implants in the palate (Advanced Molar Distalization Appliance, AMDA®) with distalization of maxillary first and second molars achieved with clear aligners (Spark®) supported by Class II elastics.

The main questions it aims to answer are:

Is there any difference in achieving upper molar distalization with the Advanced Molar Distalization Appliance (AMDA®) supported by miniscrew implants and with clear aligners (Spark®) supported by Class II elastics at the end of active distalization phase?

Is there any difference between the two groups in the anchorage loss at the end of total treatment?

Additionally, the differences in the movements of premolars, canines and incisors will be analyzed in all three planes of space (sagittal, transverse, vertical), as well as the duration of treatment between the two groups and subgroup comparisons will be performed regarding age, gender, presence of maxillary third molars and severity of malocclusion.

Participants will be randomly assigned to the AMDA® or Spark® group. Treatment will take place at the Department of Orthodontics and participants will have to visit the clinic every 4-6 weeks for regular check ups. Intraoral scans, photographs and x-rays (panoramic x-ray, cephalometric x-rays) will be taken before treatment, at the end of active distalization phase and at the end of treatment.

The aim of the study is to compare distalization of maxillary first and second molars achieved with the Advanced Molar Distalization Appliance (AMDA®) supported by miniscrew implants with distalization of maxillary first and second molars achieved with clear aligners (Spark®) supported by Class II elastics. All patients will be randomly assigned into two groups:

• Group I (AMDA®) consisting of patients that will be treated initially for molar distalization with a miniscrew implant supported device (AMDA®) and for anterior teeth retraction (after molar distalization) with the same device and fixed appliances. The miniscrew implants will be inserted in the anterior region of the palate, especially 6-9 mm posterior to the incisive foramen and 3-6 mm paramedian.
• Group II (Spark®) consisting of patients that will be treated with clear aligners for both molar distalization and anterior teeth retraction.

Lateral cephalometric radiographs of the patients' heads and three-dimensional (3D) intraoral scans of the maxillary and mandibular arches will be taken:

• before treatment (T1),
• at the end of active distalization (T2), (active distalization will be completed, when first and second molars will achieve a full Class I molar relationship (not a super-Class I), and
• at the end of treatment (T3).

Cone Beam Computed Tomography (CBCT) dental scans will be taken in patients assigned to the AMDA group:

• before treatment (T1),
• after miniscrew implant insertion (Tm) CBCT dental scans in T1 will be taken for the 3D evaluation of the anterior palate and the fabrication of a surgical guide for miniscrew implant placement. CBCT dental scans in Tm will verify accuracy of miniscrew implant placement, as well as the existence of enough clearance between miniscrew implants and the roots of upper anterior teeth to ensure a safe retraction of these teeth without the risk of contacting the miniscrew implants and the resulting root resorptions. All CBCT dental scans will be taken in a certified private dental x-ray laboratory.

Completion of orthodontic treatment of all patients will be accomplished when Class I molar and canine relationships, normal overjet and overbite, a good leveling and alignment of the teeth, and a tight occlusion of the posterior teeth will be achieved.

In all these three time points the corresponding 2D and 3D analysis will include:

• angular and linear measurements of the cephalometric analysis,
• angular and linear measurements of the virtual dental casts analysis,
• two-dimensional (2D) superimpositions of the cephalometric tracings, as well as
• 3D superimpositions of the intraoral scans of the maxillary and mandibular arches.
• superimposition of CBCT scans

All patients will be treated in the Postgraduate Clinic of the Department of Orthodontics at the Aristotle University of Thessaloniki by the applicant (Mrs. Samandara) under the supervision of Professor Papadopoulos. Assistance will be provided by the postgraduate students after insertion of the appliance, during the follow up appointments for checking and re-activating the appliances.

Inclusion Criteria:

• Patients with at least half cusp bilateral Class II malocclusion between upper and lower first molars due to maxillary excess or maxillary protrusion or forward movement of the maxillary posterior teeth, where maxillary molar distalization is indicated.
• Patients in the permanent dentition period of less than 30 years of age with second molars erupted at least one half.
• Patients with good general health and healthy periodontium.

Exclusion Criteria:

• Patients with Class II malocclusion between upper and lower first molars due to mandibular deficiency or mandibular retrusion.
• Patients with less than half cusp bilateral Class II malocclusion between upper and lower first molars.
• Patients with unilateral Class II malocclusion between upper and lower first molars.
• Patients with cleft lip and palate or with other craniofacial syndromes.
• Patients with missing, or congenital missing or supernumerary teeth.
• Patients with full coverage molar restorations.
• Patients with previous orthodontic treatment.

All collected IPD (Study Protocol, Statistical Analysis Plan (SAP), Informed Consent Form (ICF), Clinical Study Report (CSR), Analytic Code will be shared.

IPD and supporting information will be available 1 month after publication with no end date.

IPD and supporting information will be shared upon request after contacting the primary investigator of the study.