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How to extrude, intrude and expand with aligners reliably. 8 MINUTE SUMMARY

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Farooq Ahmed

How to extrude, intrude and expand with aligners reliably | Bill Layman. Click here for video podcast

Join me for a summary looking into difficult movements with aligners, why they are difficult, and a protocol derived from research on how to manage tooth movements with aligners. This lecture was given by Bill Layman at this year’s AAO, where he describes maxillary incisor extrusion, posterior intrusion, and controlled expansion.

Introduction

  • Rate of refinement: 2.5 per patient Kravitz 2022
  • 41% of aligner cases 3 refinements +
  • Switch to fixed appliances from aligners 1 in 6 Kravitz 2022

Staging and synergistic movements can reduce refinement rates

Incisor extrusion

Why is Incisor extrusion difficult?

  • Lack of undercut
  • Sqeeze teeth to engage, creating opposite effect due to V shape of a tooth – leading to loss of retention of the aligner
  • Interproximal binding through vertical contact point overlap or slipped contact points and a closed system of aligners

Incisor extrusion staging steps:

  1. Create undercut: Horizontal attachments are most effective, regardless of design Groody 2023
  2. Create 0.1mm between teeth to relieve interproximal binding
  3. First procline the incisors to increase surface contact
  4. Then Extrude and retract

Posterior intrusion

Why is it difficult?

  • Multiple teeth and lack of anchorage, through anterior teeth
  • Crowns tip mesially during intrusion as an unwanted effect
  • What happens when we intrude:
    • Mesial tipping of posterior teeth Fan 2022 Finite element
    • Buccal and palatal attachments = less tipping buccal or lingual

How to improve posterior intrusion

  • Sequential intrusion – 1st premolars
  • Tip posterior teeth 5-10 degrees distally
  • Horizontal attachment buccal / palatal
  • Consider attachment lingual Upper molars
  • Sequential intrusion
  • TADs not always needed, 5200 times bite on hard surface, enables posterior intrusion through masticatory forces

 

Controlled expansion

Why is it difficult

  • Aligners tip teeth buccally = creates occlusal interferences
  • Lack of rigidity of tray to exert forces = straight finish trays increase rigidity
  • Attempting to correct skeletal problems with dental solution
  • Greatest expansion in the premolar region
  • Expansion from the research showed progressive less posterior expansion
    • Molars expand less due to anchorage loss
  • Expansion through tipping

How to improve posterior intrusion

  • Plan around premolar expansion
  • Expect 70% in premolar region, 55% molar and 46% canine
  • Overcorrection of canines 1.7mm (premolar region 3.4mm) Zhou 2020
  • Maximum expansion seen is 4mm

Conclusion:

  • Incisor extrusion: procline teeth with attachment, then extrude and retract
    • Include iPR
  • Posterior intrusion: Start with premolars and sequentially intrude posterior teeth
    • Add distal tip
  • Controlled expansion: Effective in premolar region
    • Plan with overcorrection

Jay Bowman

  • “If you don’t build-in overcorrections you can’t get corrections”
  • “there many things that need improvement at the end that aren’t hard to do if start treatment with the overcorrections in mind”

Contributions

Contents: Shanyah Kapour

Edited and produced: Farooq Ahmed

 

 

 

 

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