Simplified Mechanics for Aligners in Treating Complex Cases Dr. Chris Chang AAO June 2021. Episode 85

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Hosted by
Farooq Ahmed

Simplified Mechanics for Aligners in Treating Complex Cases Dr. Chris Chang



Focus of lecture: pre aligner treatment, extrusion, space closure, crossbite, rotation


Chris spends 5-6 months prior to aligner treatment


TADs = pulling mechanics

Aligner = pushing mechanics


Papers on predictability of aligner movement: poorly delivered movements


·      Extraction cases:  Incisors torque loss and extrusion, molar anchorage loss and intrusion Dai 2019

·      Expansion:  Bodily movement for expansion 36% Zhou 2019

·      Incisor intrusion Charalampakis 2018

·      Second molar movement Grunheld 2017

·      Rotation of canines / round teeth Charalampakis 2018, Grunheld 2017



·      TADs

·      Power ridges

·      Attachment design

·      Over-correction

·      Pre aligner orthodontics


Pre aligner orthodontic scenarios

·      Extrusion

o   Fixed appliances to upright a molar

·      Large space closure

o   Sectional mechanics with bucco-lingual space closure

·      Deep bite cases

o   Class 3 with deep bite

o   Anterior bite turbo with flowable composite lower 3-3

·      Class 3

o   Anterior bite turbo lower arch

o   Early light short elastics 2 Oz, L2-U4

o   Open coil posteriorly to advance incisors

·      Scissor bite posterior with over eruption

o   Posterior bite block on unaffected side

o   Buccal shelf TAD on effected side

§  Intrusion and labial movement

§  Failure rate 7% Chang 2015

·      Ramus TAD

o   Rotated 7

o   14 mm

o   Horizontal insertion

o   Failure rate 5% Chang 2016

o   Nerve is lingual


Impacted canine

·      3d lever arm, 19×25 ss auxillary arm

o   U -loop to attach to elastic

o   Flowable composite to lock to

·      Infrazygmatic TAD

·      Extrude, retract and buccal movement



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