Rocking is when one side of the aligner first but the other does not. The side that is tracking will fit nicely (flushed), but the side that is tracking poorly will not want to sit at all.
Trying to sit the aligner on either side yields the same results since the aligner will react like a rubber band when stretched beyond to elastic capabilities. If you try to sit the poorly tracking side first, when you then try to sit the aligner on the tracking side, the poorly tracking side will start to lift even more at the gingival of buccal side and cause extreme pressure.
Aligners rocking can be caused by any of the following:
- The impressions used contained minor distortions
- Molars have not distalized as expected
- The arch in question has not expanded as expected
- Lack of retention
Less common causes:
- In hot climates, the aligner may have distorted from exposure to high temperatures, particularly inside vehicles.
- The patient may have had a sealant or restoration placed on a tooth unbeknownst to the dentist providing aligner treatment.
Here are some suggestions of what you can do if your patient's aligners are rocking: