Background Approximately 15% of children have a Class II malocclusion, where the maxilla is positioned anterior to the mandible, and around 90% of these children also present with an increased overjet. Increased overjet is associated with a higher risk of dental trauma and psychosocial consequences such as bullying and reduced oral health-related quality of life (OHRQoL).

Functional orthodontic appliances (e.g., headgear-activator and Twin-block) have long been used to reduce overjet through dentoalveolar effects and by influencing mandibular position and growth. More recently, digital solutions such as Invisalign's mandibular advancement appliance have been introduced, with potential advantages including improved wear time and simultaneous tooth alignment. However, there is currently limited evidence regarding treatment outcomes, patient experience, and cost-effectiveness of these newer appliances compared with established functional appliances.

Aim The primary aim is to compare treatment outcomes, patient experience, and cost-effectiveness of interceptive orthodontic treatment using three different appliances. The overall aim is to determine whether interceptive treatment of Class II malocclusion with large overjet is effective, and if so, which interceptive modality should be preferred.

Study design and setting

A total of 144 patients aged 9-13 years with Class II malocclusion and large overjet will be randomized into four groups:

• Headgear-activator
• Twin-block
• Aligner Mandibular advancement
• Control

Participants will be treated at four Orthodontic Specialist Clinics within the National Health Service in Region Halland and Västra Götaland, Sweden. Treatments will be provided by two experienced orthodontic specialists.

Follow-up and data collection

Clinical examinations will be performed at:

• Baseline (T0)
• 9 months into treatment (T1)
• End of treatment (T2) Appliance checks will occur every 8 weeks. Digital scans of the occlusion will be collected at T0, T1, and T2. Lateral cephalometric radiographs will be taken at T0 and T2.

Outcomes and planned analyses

The trial will generate three studies with distinct outcomes:

1. Treatment outcomes Primary outcome: dental treatment effectiveness measured as overjet reduction. Secondary outcomes: other dental variables, skeletal outcomes, and extraoral outcomes.

2. Patient-reported outcomes

   All treated patients will complete two digital questionnaires:

   • Child Perception Questionnaire (CPQ): assesses the child's perception of their teeth before and after treatment.
   • Orthodontic Treatment Impact Questionnaire (OTIQ): assesses the child's experience of orthodontic treatment and the appliance.

   These outcomes will be used to evaluate changes in OHRQoL from pre- to post-treatment and to compare experiences across treatment modalities.

3. Cost-effectiveness analysis The economic evaluation will include direct, indirect, and societal costs. Treatment duration, number and length of appointments, and cancellations/no-shows will be recorded.

   • Direct costs: premises, staff salaries, materials, and laboratory costs.
   • Indirect costs: parental loss of income due to absence from work.
   • Societal costs: direct + indirect costs. Costs will be related to treatment outcomes to estimate cost-effectiveness across the treatment arms.

Additional comparison: early vs late treatment Furthermore, after completing 18 months the control group, and half of the functional appliance patients will receive treatment with fixed appliances. This enables an additional comparison of early interceptive treatment versus later treatment using the same outcomes: treatment effectiveness, patient-reported outcomes, and cost-effectiveness.

Inclusion Criteria:

• Children age 9-13 years at the start of the trial
• Mixed dentition, DS3M1
• Excessive overjet ≥6 mm
• First permanent molars in at least half cusp Cl II relation bilaterally
• Incomplete lip closure

Exclusion Criteria:

• Treatment needing extractions due to severe crowding
• Earlier orthodontic treatment
• Mouth breathing
• Ongoing sucking habits
• Syndromic patients

Charing individual patient data is not approved in the ethical approval.