Clear aligner therapy. Empty promises or wishful thinking. Ki Beom Kim
Does it work well?
· Clincheck does not represent the patients final occlusal outcome Bruschang 2015
· Accuracy
o Horizontal: Predictable Charalampakis 2018
o Rotation and vertical movements: Unpredictable Charalampakis 2018
o Deep bite reduction:
§ 1.6mm Khosravi 2017
§ Lower incisor proclination 2.4 degrees
§ Overcorrection Vs no overcorrection = no differences
o Anterior openbite:
§ 3.27mm Harris 2020
§ Mostly through retroclined by 11 degrees, 1mm of posterior intrusion
§ AOB cases showed no molar intrusion Garnett
Biomechanics
· Torque
o To torque with aligner – greater force required at the cervical aspect
o Aligner does not seat with torque at cervical aspect, therefore no effective force for torque Hahn 2010
o Root discrepancy of planned and delivered = 2mm for root change = little root change
o Aligner strength
§ Strongest aspect of aligner – Incisal aspect
§ Weakest aspect of aligner – gingival aspect
§ = Invisalign tend to not adapt well to gingival margin and therefore torque movements not achieved
· Intrusion
o Proclination of teeth
o Buccal attachment = further proclination
o Lingual attachment – little counter moment
o Retrocline incisors during rotation – helps to achieve pure intrusion resultant force
Antagonistic and synergistic movement
· Incisors:
o Buccal tipping and extrusion Vs Buccal tipping and intrusion
o Lingual tipping and intrusion Vs Lingual tipping and extrusion
Attachments
· Rotations added to typodont, different attachments buccal, lingual and adjacent teeth Momtaz 2017
o 60% with no attachments
o more Attachments on adjacent teeth, reduce accuracy down to 27%
· We don’t truly know how attachments work
o What size, direction, active surface shape
Accuracy of aligner outcomes
· 77% accurate for tipping Wheeler 2017
o However tipping most accurate movement
· 50% overall movements 1ST set of aligner Haouili 2020
o 1st refinement 75% accuracy
· ABO 80% fail, fixed 50% fail Djeu 2005
Extraction of upper 1st premolars
o Finite model analysis, showed uncontrolled tipping upper incisors Jiang 2020
o Patients molar anchorage loss 2.3mm, mesial rotation 5 degrees, reduced retraction of incisors, only 2mm of retraction, Retroclination of upper incisors 5 degrees, Dai 2019
Ki study
o Observed adjacent teeth to moving teeth:
o Unpredictable movement of adjacent teeth = biomechanics more complex
o Occlusal forces change resultant forces?
Development
o Scrapy East Asia material – currently experimental
o Direct to printing, save costs
o No polishing
o Alter aligner thickness
superb