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:

o  
Mesial tipping of posterior
teeth Fan 2022 Finite element

o  
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

o  
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

o  
Include iPR

·      
Posterior intrusion: Start with
premolars and sequentially intrude posterior teeth

o  
Add distal tip

·      
Controlled expansion: Effective
in premolar region

o  
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