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:
4. Incisor intrusion
5. Deep bites
The details below describe how to resolve the reduced predictability of aligners.
· 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.
· 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.
· 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.
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.