Distal Upper Molar Force Distribution With Clear Aligners Using Different Anterior Teeth Anchorage Setups: A Finite Element Study.

Abstract

<h4>Objective</h4>The notion that clear aligners alone can distalize upper molars without affecting anterior teeth is inaccurate. Although strategies such as Class II elastics, tooth-movement sequencing, and attachment variations have been investigated to mitigate unwanted side effects, temporary anchorage devices have demonstrated potential for maintaining anchorage during molar distalization. This study used Finite Element Analysis to evaluate different setups for distalizing one or both upper molars, comparing passive anchorage (ligature tie) and active anchorage (1.66 N), and assessing the presence of vertical attachments.<h4>Materials and methods</h4>Six models were generated with 0.2 mm distal activation for molar distalization. These models varied by premolar/M attachments and anchorage type-active (1.66 N) or passive-applied from extra-alveolar screws to canine buttons.<h4>Results</h4>All setups distalized the second molars, but passive anchorage demonstrated greater efficiency and fewer side effects. Passive systems achieved over 90% distalization-to-anchorage loss ratios, compared with 65% with active forces. Passive setups also minimised unintended anterior movement and enabled distal canine movement following molars-an advantageous outcome. Vertical attachments had minimal impact. X-axis (midline) movement predominantly affected canines, particularly with active anchorage. Anterior intrusion on the Z-axis was reduced with passive systems.<h4>Conclusion</h4>Active anchorage forces may deform aligners and compromise control, whereas passive anchorage-similar to a ligature wire applied to anterior teeth-supports planned movement without disrupting biomechanics.