Join me as I summarise the 1st day of the Saudi Orthodontic Clear Aligner meeting, where Mazyar Moshiri delivered a masterclass on biomechanics with aligners.

Conclusions:

· Attachment design: perpendicular to resultant force

· Rotations: Place oblique attachment to counter intrusive force of aligner

· Overcorrect torque, add mesial crown tip due to wagon wheel effect

· Deep bite: synergistic movements: proclinatiion and extrusion

· AOB: synergistic movements: retroclination and extrusion

Concepts

Intrusion attachment

1. Intrusion on aligners

a. No intrusion attachment

o Require attachments on adjacent teeth

o If loss of tracking = occurs on adjacent teeth, with the aligner extruded off the teeth

Rotation and intrusion

· Force labial face and palatal face to create rotation moment.

· ‘Squeeze force’ occurs =  vertical force = intrusion force.

· Solution

o Optimised attachment = Extrusive vector, usually gingival bevel and oblique

o Resolve resultant force, horizontal and vertical = oblique attachment

Torque

· Wagon wheel effect, for every 4 degrees of lingual crown torque there is distal crown tipping / mesial root tipping.

o Solution: OFFSET with 1 degree of mesial crown tip

· Torque lags behind, takes longer , like rectangular NiTi archwire

· Buccal root torque: Upper molar buccal attachment to provide extrusive buccal force to create moment.

Design of attachment

· KEY CONCENT: Attachment perpendicular to the force

· Perpendicular force to rotation = Long vertical attachment

· But rotational force has intrusive force the ‘squeeze force’

o Therefore horizontal and vertical force = attachment perpendicular to the force = oblique attachment

Root tip

· Open space 0.2mm interproximal =  so more plastic wrap around tooth

· Then start root movement in staged way.

Deep bite

Concept:

Synergistic movements, procline = relative intrusion

Staging AP movements

o Proclination 1st to open the bite

o Then IPR

§ Not at the same time as IPR = retroclination, therefore should not procline and iPR at the same time as bite will  not open

§ Does round trip – procline and intrude, then IPR and align

Staging deep bite

· Staging of OB, canines intrude 1st, then 2-2

· Likely loose tracking on lower incisors or 4s – anchorage horizontal G5/G7 attachments

Curve of Spee

· If COS not corrected, then AP also difficult to correct

· If not correct COS:

o Posterior openbite – caused by anterior interferences

§ Caused by inadequate attachment

§ Lack of over correction

OGN case deep bite

· Order 10 passive aligners near end stage pre surgery = minimum 2 months to make up for ‘lag’ or vivera retainer / essix – thicker, greater expression of torque

· TAD – intermaxillary elastics x 2

o TAD maxilla:

§ Buttons lower premolars

§ Intermaxillary elastics to guide lower premolar teeth into the tray

Openbites

Concept

Synergistic movement: Retrocline and extrude

· Aligners do not extrude along the long access

· Aligner pushes tooth lingually and extrudes in the process, retroclines

Posterior intrusion is unpredictable, anterior extrusion is more likely

Thank you to the Saudi Orthodontic Society for facilitating this podcast