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Distal Upper Molar Force Distribution With Clear Aligners Using Different Anterior Teeth Anchorage Setups: A Finite
Weber Jose da Silva Ursi1, Yamyle Claudia Velásquez Barragán2, Ki Beom Kim3
1Department of Social and Clinical Pediatric Dentistry, Dental School of São Paulo State University, São José dos Campos, São Paulo, Brazil.
Orthodontics & Craniofacial Research
|December 13, 2025
Summary
Passive anchorage is more effective for clear aligner molar distalization, minimizing side effects like anterior tooth movement. Active anchorage forces can compromise aligner control and treatment outcomes.
Area of Science:
- Orthodontics
- Biomaterials Engineering
- Dental Mechanics
Background:
- Clear aligners are increasingly used for orthodontic treatment, but achieving controlled molar distalization without affecting other teeth remains a challenge.
- Various strategies, including Class II elastics and attachments, have been explored to improve molar distalization with clear aligners.
- Temporary anchorage devices (TADs) offer potential for enhanced anchorage during clear aligner therapy.
Purpose of the Study:
- To evaluate the effectiveness of different clear aligner setups for distalizing upper molars using Finite Element Analysis (FEA).
- To compare passive anchorage (ligature tie) versus active anchorage (1.66 N force) for molar distalization.
- To assess the influence of vertical attachments on molar distalization outcomes.
Main Methods:
- Six FEA models were created to simulate molar distalization with 0.2 mm distal activation.
- Models differed in premolar/molar attachments and anchorage type: passive (ligature tie) or active (1.66 N force).
- Anchorage was applied using extra-alveolar screws or canine buttons.
Main Results:
- All tested setups successfully distalized second molars.
- Passive anchorage systems were more efficient (over 90% distalization-to-anchorage loss ratio) and had fewer side effects than active systems (65%).
- Passive anchorage minimized unintended anterior tooth movement and allowed for beneficial distal canine movement, unlike active anchorage which caused significant midline (X-axis) canine movement and anterior intrusion (Z-axis).
Conclusions:
- Passive anchorage, akin to a ligature wire, provides superior control for clear aligner molar distalization compared to active forces.
- Active anchorage forces may deform clear aligners, compromising treatment control and biomechanics.
- Passive anchorage supports planned tooth movements without disrupting the overall biomechanical system.
