Hyperdivergency Treated with Aligners

Posterior Intrusion with TAD’s and Aligners

by Dr. Daby Robert, DMD

For years now, it’s been known that fixed orthodontics tends to open the vertical dimension, especially when treating in permanent dentition. Since the coming of clear aligners, studies shows that vertical dimension is more easily controlled with aligners than fixed brackets.

It’s been widely advocated that aligners can cause posterior open bites, which is not always a good thing depending on our treatment needs. It must be kept in mind that aligners can cause posteriors open bites (POB) in known clenching or bruxing patients. For this to happens in non-clenching patients, some studies suggest that the thickness of the materials should exceed the posterior freeway space, which should be approximately 3-4mm to create a sustained bite block effect.

Spark aligners as recently developed bite turbos which have a thickness between 0.5 and 1.7mm, which combined with clenching exercises can lead to slight posterior intrusion. One must be careful to ensure TMJ are healthy and asymptomatic before using this technique.

Furthermore, we should consider the use of temporary anchorage device (TAD’s) if we expect more predictability and more intrusion.

Dr Chris Chang is a widely know user of those TAD’s for multiples movements. There are different ways to perform posterior intrusion. One of them is to place buccal and palatal TAD’s and have the patient run an elastic from the buccal to the palatal over the aligners. Precautions must be taken not to interfere with roots while TAD’s insertion. This technique is useful for “en masse” intrusion of posterior segments and may prevent unwanted torque compared to only placing TAD on buccal or on palatal. It is not necessary to program intrusion in the aligners as it is impossible to know the exact intrusion rate that will express. The TAD’s and elastics themselves will produce intrusion. Studies suggest that you can expect intrusion somewhere between 0.3 and 1mm a month depending on root anatomy.

Another way of using TAD’s for ‘’en masse’’ intrusion has been developed by Dr. Aldo Giancotti and al. which use an 18x22SS wire with a hook bonded on the posteriors. Cut-outs are planned in the aligners to leave room for bonding the wire/hook. The TAD’s are then inserted buccally then an elastomeric chain is runned from the TAD to the hook. They advise to not plan any intrusion in the aligners cause it’s impossible to predict the rate of the intrusion that will happen. I would recommend placement of horizontal attachments on posterior teeth to assure the aligners will follow the intrusion movement so that you keep control.

A method useful especially in the mandible cause lingual TAD placement is almost impossible is to have either a button or elastics cut-outs on the lingual of the 6’s and TAD’s placed on the buccal aspect of the arches. Patient then places elastics from the TAD’s to the buttons or cut-outs over the aligners. This way, we have all the buccal portion of the tooth for attachments placement to control the torque while intruding. We then need to add buccal root torque to control the dumping of the crown that can occur buccally by the force’s vectors given by the elastics.

Finally, bonding buttons directly on the aligners with one TAD on each side is, beside having buccal and palatal implant, the best way to have maximum control of the teeth being intruded. Only matter with this option is that you have to bond buttons on every single aligners while the intrusion takes place.

If you’re preferred method is to bond buttons directly on the buccal of to teeth with buccal TAD’s, my advice would be not to plan big movements on the teeth intruding cause even with big attachments, the intruding teeth may outrun the aligners so keep a good eye on the tooth movement table.