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.