Skeletal and Dentoalveolar Effects of Functional Clear Aligner Therapy in Growing Patient With Skeletal Class III Malocclusion

. Fifteen patients with mild skeletal class III were selected according to specific inclusion criteria and included in the study, these patients were treated with Functional Clear Aligner to evaluate its skeletal, dentoalveolar & soft tissue effects.

Bite registration: The patient intraoral scan will be performed according to the constructor's instructions. The software interface of the intra-oral scanner allows the registration of two different maxillo-mandibular relationships (MMRs).The first MMR scan will be registered in maximum intercuspation occlusion. The second scan will be registered in planned mandibular retrusion for Aesthetic functional appliance design. Bite registration will be done with the mandible in the most retruded position with an inter- incisal clearance of 2 mm and a clearance of 6 mm in the posterior segment.

To obtain an optimal and reproducible MMR scan in mandibular retrusion, curable resin will be used as a bite registration material. Two pieces of resin will be used as bite registration material, placing them (one piece per each side of the dentition) onto the occlusal surface of the posterior dentition. Then mandible will be guided in the most retruded position, this will be performed with a brief preliminary patient training. When the mandible reaches the desired backward position, the occlusal resin will be cured on both sides. Then the two registration pieces of resin will be fully cured outside of the mouth.

Once fully polymerized they will be checked for integrity, and they will be placed in occlusion to check that final mandibular retrusion is adequate and conforms to planned retrusion. Subsequently, patient maxillo-mandibular relationship in mandibular retrusion will be scanned.

During MMR scan acquisition on the right side, only the left piece of resin will be used to maintain mandibular retrusion. Conversely, during MMR scan acquisition on the left side, only the right piece of resin will be used. At the end of the MMR acquisition process, the software will be able to reorient the maxillary and mandibular scan according to the MMR.

Appliance construction: The steps of appliance construction are as follows:

• Import of Digital Scans Digital intraoral scans of the maxillary and mandibular arches are imported into the orthodontic planning software.
• Software Planning and Treatment Setup All software planning steps are performed, including model alignment, occlusal setup, and registration of the construction bite.
• Placement of Attachments Optimized attachments are digitally placed on selected teeth to enhance aligner retention and control tooth movement.
• Design of Mandibular Advancement Blocks A second design phase is performed to incorporate the mandibular advancement blocks. A total of four blocks are digitally designed, with two blocks placed in the maxillary aligner in the anterior region and two blocks placed in the mandibular aligner in the posterior region. The blocks are designed as inclined planes to guide mandibular repositioning, simulating the reverse twin block mechanism. The upper and lower bite blocks are designed to interact with each other through coherent, specifically designed 70° inclined planes, allowing controlled mandibular repositioning during occlusal contact.

After the design process, the generated three-dimensional models are exported as files with STL extension and produced using different procedures according to their specific purposes.

• 3D Printing of Aligner Models The finalized digital files are used for three-dimensional printing of the aligner models.
• Thermoforming of Clear Aligners Clear aligners are fabricated by thermoforming thermoplastic sheets over the printed models.

The appliance construction workflow, including digital scanning, virtual treatment planning, attachment design, mandibular advancement block construction, STL file export, three-dimensional printing, and thermoforming of clear aligners, was performed according to previously described digital orthodontic and clear aligner protocols.

Clinical application:

• Bonding of Attachments

Composite attachments are bonded on the facial surface of upper and lower central incisors and the upper and lower first permanent molars according to the digitally planned attachment design:

Intra-oral bonding procedure will be started with the etching of the facial surface of the maxillary and mandibular central incisors and first permanent molars with (Meta Etchant) for 15-20 seconds. Etched dental surfaces will be washed and dried with chair air-flow and light-cured dental bonding agent (ORTHOSOLO from Ormco) will be applied to the conditioned dental surfaces and then polymerized for 5 seconds.

The Attachments Template is loaded with the bonding material (SimpliShade TM Bulk Fill Flow composite from KERR TM) and positioned over the planned teeth to ensure precise placement of the attachments.

Then the bonding material will be polymerized for 60 seconds for each attachment, and the template will be carefully removed and then the excess composite will be removed with Tungsten carbide orthodontic bur.

Proper positioning and adaptation of the attachments are clinically verified to ensure optimal aligner retention and effective force delivery.

• Appliance Delivery The maxillary and mandibular clear aligners incorporating the reverse twin block design are inserted intraorally. The fit and proper seating of both aligners are carefully checked.
• Occlusal Verification The interaction between the upper and lower bite blocks is evaluated to confirm correct engagement of the inclined planes during mandibular closure. The mandible is guided into the predetermined therapeutic position upon occlusal contact.
• Patient Instructions Patients are instructed to wear the clear aligners for 20-22 hours per day, removing them only during meals and oral hygiene procedures. Detailed instructions regarding insertion, removal, cleaning, and storage of the aligners are provided.

The clinical procedures, including bonding of attachments using a template, appliance delivery, occlusal verification, and patient instructions, were performed according to established protocols for clear aligner therapy.

Inclusion criteria

• Patients' age (8-11) years (CVM stages 2-3)
• Mild class III skeletal pattern (Wits appraisal = 0 to -8)
• Mild to moderate reverse overjet (-1 to -4)
• Overbite (1-5)
• Growing patients
• Average or below average maxillary-mandibular plane angle and lower facial height
• Mild incisors compensations

Exclusion criteria

• Severe class III skeletal pattern
• Long facial height
• Bad oral hygiene
• Systemic condition that may interfere with treatment