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 Orthodontist, 87(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 Orthodontist, 89(5), pp.679-687.