Tech tip: Why aren't the posterior teeth in occlusion?

Question:

As my patient’s treatment nears its end, I’m noticing that the upper & lower anterior teeth are touching when the patient bites down, but the posterior teeth are not in occlusion. What’s going on?

Answer:

There are many possible causes of this situation. This phenomenon is fairly common with clear aligners, and it’s usually 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 usually intrude slightly to make room for the aligner, as the patient clinches his or her jaw throughout the day. 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.

This is not typically a big concern, however, because the posterior teeth will usually super-erupt back into normal occlusion as soon as they get a chance. 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. Another option is to prescribe a Hawley retainer which won't interfere with occlusion, allowing the posterior teeth to super-erupt freely.

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