A posterior open bite is when the upper & lower anterior teeth are touching when the patient bites down, but the posterior teeth are not in occlusion.
There are many possible causes for a posterior open bite and it is fairly common with clear aligners. Usually it's temporary. It can be caused by the “hinging” action of the jaw.
Imagine placing a 1 mm sheet of flat plastic over the occlusal & incisal surfaces of the lower teeth. As the jaw closes, the posterior teeth will contact first. The patient would have to bite down firmly to get the anterior teeth to touch completely.
The same thing can happen when the teeth are covered by clear aligners. When the patient first starts wearing them, the posterior teeth are the first to contact. After wearing the aligners for a while, the teeth adjust to compensate, and before long, the patient can bite evenly with the aligners on.
The posterior teeth will intrude slightly to accommodate for the thickness of the aligners as occlusal forces are applied. Once the teeth have adjusted to the aligners, if the patient removes the aligners and bites down, the anterior teeth will make contact first and the posterior teeth probably won't quite touch.
Here are some common approaches for a posterior open bite.
For posterior open bites present during clear aligner treatment:
- Remember to check the occlusion during treatment visits and look for signs of posterior open-bite. Request a revision to slightly intrude the anterior teeth by ~0.5mm - 1.0mm on both arches, depending on the amount of open-bite. This relative intrusion will allow the posterior teeth to extrude, thereby closing the posterior open-bite.
- To assist with re-establishing posterior contact, an open tray approach can be taken. Cutting off the aligner at the terminal molar to establish contact and gradually working your way forward until a canine to canine tooth aligner is left and posterior contact is established.
For posterior open bites present after clear aligner treatment:
- After the patient has worn the final retainer for 3-6 months and the teeth are stable, the patient can switch to wearing the retainer on alternate days to give the posterior teeth freedom to move back into their normal position.
- Or you can have the patient try the combination of wearing the upper retainer one night and lower the next and so on.
- A Hawley retainer could be prescribed, which won't interfere with occlusion, allowing the posterior teeth to super-erupt freely.
- A fixed retainer is also another option.
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Until next time...