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Aligners with TADs Chris Chang. Episode 25. September 9th 2020

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Hosted by
Farooq Ahmed

Chris Chang describes the use of aligners (Invisalign), and how to resolve common aligner issues and incorporate TADs to achieve predictable outcomes.

Aligners work as a pushing appliance:

·      Pushing surface (active surface) should be at 90 degrees to the direction of tooth movement.

·      Pulling movements can be achieved through combining with TADs.

Reduced aligner predictability:

1.     Distalisation

2.     Expansion

3.     Extraction

4.     Incisor intrusion

5.     Deep bites

The details below describe how to resolve the reduced predictability of aligners.

1.     Distalisation

·      Aligners cannot distalise teeth en-mass, and require sequential distalisation but with incorporating TADs it is possible, for example:

o   Distalisation in the lower arch:

§  Buccal shelf TAD in the lower arch (vertically placed, lateral/ buccal to the lower molars).

§  Intra-arch elastic wear  (4.5 ounces) from the lower canine to terminal molar.

2.     Expansion

·      Aligners result in tipping (buccal flaring) with expansion, this can be resolved through attachment placement:

o   Long horizontal attachment placed buccally with a gingival bevel.

§  Stage 1 of expansion = Buccal flaring.

§  Stage 2 of expansion = Attachment aligner interaction results in pushes force palatally, the balancing of moment results in –

Buccal root torque = uprights tooth = bodily expansion

 

3.     Premolar / bicuspid extractions & 4. Incisor intrusion

·      Aligners result in tipping of teeth into the extraction site, this can be resolved through creating a counter moment through attachments

o   G6 optimised attachments have their pushing surface / active surface positioned to counter the tipping movement and bodily translate the tooth

o   G6 attachments are located at different heights to generate a force in the direction desired and creating a counter moment.

o   Kenji formula: change G6 attachments to  long vertical attachments

 

·      Aligners and extractions can also result in (Fan-fan Dai 2019):

o   Incisor extrusion and torque loss.

o   3mm of posterior anchorage loss and intrusion of molars.

Correction

·      TAD placed in upper incisor region, and elastic wear:

o   2 anterior labial TADs – intrude anterior teeth

§  Elastic from palatal cut out of aligner over occlusal surface to labial TAD.

o   2 posterior buccal TADs preserve anchorage

§  Elastic wear from canines to TAD for retraction

5.     Deep bite

·      Aligners under correct deep bites due to the bite plane affect, this can be resolved with a 3 stage approach

1.     Overcorrection of Deep bite in planning.

2.     Chewies – on the anterior teeth.

3.     Incisor screw – incisor intrusion with elastics.

Anterior Crossbite tips

1.     Occlusal attachment – to open the bite.

References

Grünheid, T., Loh, C. and Larson, B.E., 2017. How accurate is Invisalign in nonextraction cases? Are predicted tooth positions achieved?. The Angle Orthodontist87(6), pp.809-815.

Dai, F.F., Xu, T.M. and Shu, G., 2019. Comparison of achieved and predicted tooth movement of maxillary first molars and central incisors: First premolar extraction treatment with Invisalign. The Angle Orthodontist89(5), pp.679-687.

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