Posterior Open Bite

For information regarding posterior open bite, refer to the following:

• Definition
• Causes
• Solution

Definition

A posterior open bite occurs when the patient bites down and only the anterior teeth come into contact although the posterior teeth are not in occlusion.

Causes

There are many possible causes for a posterior open bite, and accordingly, different methods of resolving this undesirable phenomenon. In this article, we will only discuss open bites associated with aligner treatment.

By far, the most common etiology for a posterior open bite concurrent with aligner treatment is when the mandible advances bringing the lower anterior teeth into premature contact with the upper anterior teeth. The advancement results from the "relaxation" or "re-posturing" of the musculature as the aligner treatment corrects the deep bite that has forced the mandible into a strained, distally displaced position. The reduction of the interdigitation of the occlusal surfaces of the upper and lower teeth due to the aligners, in conjunction with the reduction of the restricting deep bite, eliminate the factors holding the mandible back, so the mandible comes forward.

A less probable etiology comes when some clinicians have hypothesized that the ≈1.5 mm (the approximate thickness of 2 layers of aligner material) between the teeth when the aligners are worn will cause the posterior teeth to intrude under the biting forces, resulting in the posterior open bite. This model does not appear to withstand scrutiny, however, when one considers that the "biting forces" actually only come into play a fraction of time during a 24-hour period, unless the patient is a heavy bruxer. Additionally, there have been no studies documenting intrusion of the molars by aligners that have no intrusion staged in them.

Solutions

It is very important to monitor cases very carefully to observe if a posterior open bite develops during an orthodontic correction with clear aligners. Check before using the last few aligners, so if a revision is necessary to close the posterior open bite, it can be done expeditiously.

If the clinician believes a slight open bite is caused by molar intrusion and there is not heavy contact between the anterior teeth:

• Remove the aligner material covering the “intruded” molar(s). This may allow the intruded teeth to settle back down into occlusion with the opposing teeth without requiring a revision.
• The settling can be expedited by bonding buttons or brackets on the buccal of the offending teeth and stretching elastics between the upper and lower teeth to pull the open bite closed.

Most likely, heavy, premature contact between the anterior teeth has resulted from the advanced re-positioning of the mandible causing the posterior open bite. In these circumstances:

• Request a revision asking for upper incisor intrusion and proclination, and lower incisor intrusion in order to eliminate the heavy, premature contact so the posterior teeth can come together
• Remember to re-impress or re-scan to replicate the posterior open bite as it currently exists so the technician can see how much they have to re-position the anterior teeth.