Treating complex aligner biomechanics. Willy Dayan. Episode 82. June 2nd 2021

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Hosted by
Farooq Ahmed


Join me as I summarise Willy Dayan’s lecture looking at biomechanics in AOB, class 2 and extraction cases




Question is not if we can do Invisalign, like asking a sports star do they do Nike, it may be the best equipment but it comes down to our skill as clinicians


  • Don’t think of clincheck as video, think of the clincheck as delivering force to teeth


Case selection

  • Do all fixed cases have the same number of wires / aligners
  • Biological limitations – software cannot plan, clinical decision


Cases where we shouldn’t idealise occlusion

  • Severe skeletal 3, bilateral crossbite, hypoplastic maxilla, accept discrepancy
  • Spacing cases: open up for 5th lower incisor, prevents over retraction
  • Avoid over expansion upper arch, exaggerate lower lingual crown torque


Vertical control

  • AOB: with aligners can close without elastics through staging:
    1. Molar intrusion with premolars anchorage
    2. Premolars intrusion, anterior teeth anchorage

= Lateral openbite in treatment but corrected when premolars intrude and autorotate



Sagittal correction

2 methods

  1. Sequential distalisation, utilising anterior anchorage for individual distalisation
  2. Bite jump
    • What is it: overjet increases in the clincheck, posterior teeth don’t move
    • However with class elastics the maxillary teeth distalised


Bicuspid / premolar extraction cases

Can have the following effects

  1. Loss of anterior torque
  2. Reverse curve of spee in the upper, and curve of spee lower
  3. Roots not parallel Gable


  • Increase anterior torque,
  • Lingual vertical attachments to achieve parallel roots
  • Excessive gable bends to compensate for unwanted tipping
  • Curve of spee upper, reverse curve of spee lower arch
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