Managing Complex Cases in Orthodontics. Kleber Meireles and Andre Machado

Join me for a summary of a dynamic conversation between Kleber and Andre, It was a lecture full of biomechanics and the podcast will focus on specific examples with fixed appliances and aligners.

Fixed appliance mechanics

1. Canine retraction in extraction case with buccal canine: sectional mechanics

o Conventional sliding mechanics retract canine but also distally tip and rotate distal in

o Loop mechanics

§ Mechanics = canine retraction – line of force buccal

§ Side effects = no distal in rotation due to line of the force buccal

§ Mechanics = sectional mechanics allows counter moment to increase as canine retracts = bodily retraction

§ Side effect = no distal tipping of the canine

2. Retraction of upper anterior teeth in extraction cases

o Loss of anterior torque on retraction,

o Torque mechanics:

§ Stop active space closure

§ Apply anterior buccal crown torque

§ When recovered, continue final space closure

Aligner biomechanics

Comment:  Physics is physics & there is nothing magical appliance

Distalisation with aligners

· Not effective with aligners

· Mechanics: Distal tip

· Side effects: No root movement

Solution

· Attachments for molar distalisation:

o 6mm:  horizontal requires 120g, 10mm from the CoR = 1200gm force required for counter moment, however no aligner material can deliver this force or provide retention to the force, therefore not effective tooth movement

o 4mm attachment requires greater force, 1200/4 = 300g

Issues with aligners

· Rely more on companies to do the treatment planning

o AI does not have knowledge of the roots and its angulation – which is difficult to correct even with conventional braces

· Lack of stiffness in the aligners make it difficult to apply counter moment

o For example incisor retraction in extraction cases

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I hope to see you Porto for the Simply Ortho congress on the 9-11 of June