Search

Biomechanics and Force Delivery Systems- Wires to Screws to Plastic Ravi Nanda 2021 Edward H. Angle Award Lecture. AAO June 2021. Episode 87

Play episode
Hosted by
Farooq Ahmed

Biomechanics and Force Delivery Systems: Wires to Screws to Plastic  Ravi Nanda

2021 Edward H. Angle Award Lecture

 

Edward Angle textbook

Some innovations today relate to Edward’s appliances

·      Expansion arch

·      Single tie bracket

·      Headgear

·      Biomechanics

o   Pushing, pulling and rotational forces

·      Bakers anchorage = class 2 elastics

 

 

Brackets

·      Significant number of studies, however relate little to the outcome

 

Archwires

·      Significant change to biomechanics with NitI

·      Properties of NiTi wire, show larger wire requires greater deflection to achieve superelastic plateau, delivers higher force  Pesce 2011

o   Ravi recommended using larger wires to give greater control

·      Location of the bend can result in variation in moment depending on location

·      Example of class 2 and moments

o   Molar correction: using a simple lever arm through the molar and premolars to distalise molar, followed by class 2 elastics to retract

 

Force Vs moment

·      Ravi says moment is more important than the amount of force, for example headgear, 500g is less important than the direction of moment from the outerbow

 

TADs and biomechanics

·      Learning from experience: Direct retraction on TADs in class 2 cases results in increase in overbite  Davoody 2012

·      Directing moment at different points of the cenre of rotation changes the type of tooth movement – Ravi 2014 JO

·      Infrazygmatic TAD can be applied to retract the upper incisors and passivng the moment through the centre of rotation of the anterior teeth = retract and no increase in overbite

·      Buccal shelf TAD: in class 3 case with AOB, powerchain results in retraction for AP as well as counterclockwise rotation which closes AOB

 

Aligners

·      Started with clinicians depending on the company on how to move the teeth

·      Advances in aligners and engagement with biomechanics = force delivery through deformation of plastic

o   Pressure area, attachments, auxillaries

·      Force from different levels of activation of aligners Li 2016 KJO

o   Varied of activation 0.2-0.6 and force loss

§  0.2mm activation with time results in loss of force up to 40% at 7 hours

§  Initial force 8 Newtons at 7 days 2 Newtons

 

·      AOB cases and aligners Harris 2020

o   Most correction occurs through retraction and IPR, relative extrusion of upper and lower incisors, not molar intrusion

 

Aligner Attachment

·       Different attachment design for canine teeth Ojima in press paper

o   Conclusion:

§  Did not matter shape of attachment, the moment was key

§  Without attachment uncontrolled tipping

 

Author

Join the discussion

More from this show

Your subscription could not be saved. Please try again.
Your subscription has been successful.

Never miss an episode or blog!

Subscribe now