Indications and application of minimum anchorage mechanics Vishnu Raj. Episode 142. November 23rd 2021

Indications and application of minimum anchorage mechanics Vishnu Raj

Join me for a summary of Vishnu Raj’s lecture looking at minimum anchorage mechanics, with a focus on utilising Burstone’s Geometries for a simple and effective way to manage anchorage, a well explained lecture with useful tips.

Indications

Classification

• Group C minimum anchorage
  • 75% or greater posterior movement into the extraction space
  • Incisor movement minimal

Indications

• Mild anterior crowding
• Posterior crowding, ectopic 2n molars
• Missing 5s

Aetiology of crowding

• Compared to pre-historic man = 30% increase = greater likelihood of impaction of 8s and 7s

2^nd molar eruption – posterior crowding associated with Hwang 2017

• Wider teeth and crowding
• Maintenance of E space

Premolar extraction and posterior crowding Turkos 2013

• Increase space for 3^rd molars
• Mesial movement of 1^st and 2nd molars
• Mesial movement molars = 3.2-4.6mm

Biology and mechanical considerations

Anchorage considerations

• Upper molars move more mesial then mandibular molars due to :
  • Growth of mandible
  • Bone type and density
    • Cortical bone more resistance to tooth movement Devlin 1998
      • Posterior maxilla = 0.31gcm2
      • Anterior maxilla 0.55 gcm2
      • Mandible 1.11gcm2
    • Upper incisors tend t retract less then lower incisors Gu 2017
      • Large root surface area upper 2-2
      • Prescription torque upper high – anchorage loss

Preparing anterior anchorage

• Allow working archwires to be passive for 4-6 weeks
• Start space closure 1-2 weeks after extractions
• Curve in archwire to accentuate inclination to resist over retraction
•  
• Increase 2^nd order 2-2
• Increase 3^rd order 2-2
• Elastics

2^nd order bend what is it

• Gable bend or V bend 15-25 degrees
• Bend closer to anterior segment
• 6 geometries between slots Burstone 1988
• Effects:
  • Increases anterior anchorage
  • Root parallelism

Increase 3^rd order

• Increase stiffness SS,
• Torsional stiffness SS:TMA:NitI 10:3:1
• increase cross section 21×25

Decrease wire slot engagement angle

3^rd order bend

Conclusion

• Posterior crowding to be considered
• Mesial movement 1^st molre more predicable to resolve posterior crowding
• Anterior anchorage
• Control of incisor and lip position

Conclusion

Posterior crowding to be considered

Mesial movement 1^st more more predicable to resolve posterior crowding

Anterior anchorage

Control of incisor and lip position