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
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 :
- 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
- Cortical bone more resistance to tooth movement Devlin 1998
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:
- Increases anterior anchorage
- Root parallelism
Increase 3rd order
- Increase stiffness SS,
- Torsional stiffness SS:TMA:NitI 10:3:1
- increase cross section 21×25
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
Conclusion
Posterior crowding to be considered
Mesial movement 1st more more predicable to resolve posterior crowding
Anterior anchorage
Control of incisor and lip position
Very interesting and informative from a historical perspective and vital to understand at the initial stages of ones career.
However ,in my view,long superceded by more other techniques that better lend themselves to a busy practice.
EG.Damon style mechanics,NOT necessarily Damon brackets.
Full disclosure,I have absolutely no ties ,of any kind,with Ormco or any other dentl/ortho .company.