Indications and application of minimum anchorage mechanics Vishnu Raj

orthodontics In summary

Indications and application of minimum anchorage mechanics Vishnu Raj

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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

o 75% or greater posterior movement into the extraction space

o 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

2nd 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 3rd molars

· Mesial movement of 1st 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 :

o Growth of mandible

o 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

o Large root surface area upper 2-2

o 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 2nd order 2-2

· Increase 3rd order 2-2

· Elastics

2nd 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:

o Increases anterior anchorage

o Root parallelism

Increase 3rd order

· Increase stiffness SS,

· Torsional stiffness SS:TMA:NitI 10:3:1

· increase cross section 21x25

Decrease wire slot engagement angle

3rd order bend

Conclusion

· Posterior crowding to be considered

· Mesial movement 1st molre more predicable to resolve posterior crowding

· Anterior anchorage

· Control of incisor and lip position