When it comes to clear aligners, keeping treatment on track can be a challenge.
There are a number of variables that can affect clear aligner treatment and prevent aligners from tracking the way you intended.
These variables include:
- Tooth shape
- Type of tooth movement (some are more predictable than others)
- Patient compliance
- Lack of available space (tight contacts)
- Insufficient pressure
A 2013 study conducted by Chisari et al. and published in the AJODO followed orthodontic tooth movement over time and documented factors affecting tooth movement including age, sex, root length, bone levels, and bone density. Difficult movements such as rotations, intrusions and extrusions were particularly unpredictable.
In the study, clear aligners were programmed to move 1 central incisor 1 mm over the course of 8 weeks. At the end of the study, the mean tooth movement was only 57% of the planned goal.
Figure derived from "Variables affecting orthodontic tooth movement with clear aligners; Chisari et al, 2014". The plotted tooth movement is an average of 3 study groups.
Because of these variables (and others), clear aligner therapy can be somewhat unpredictable. Some clinicians will notice discrepancies right away, but a lack of tracking can also accumulate over time.
So, what's the solution?
If you can anticipate potential tracking issues and adjust your treatment goals and techniques accordingly when submitting the case, you can help the required tooth movements track better throughout treatment.
The next logical question then is; "How do I anticipate and manage potential tracking issues?"
Another thing to look for is the discrepancy between the tooth size (mesial incisal edge to distal incisal edge) and the size of the space that the tooth is attempting to move into. If the space is not big enough, then the tooth will not move adequately into this space and could cause additional tight contacts.
While you and your patient prefer to avoid revisions they are sometimes necessary in order to achieve desired treatment outcomes—especially to acheive difficult movements.
When you request a revision, you can request additional IPR (as was necessary in the example above), engagers, or overcorrection in order to get treatment back on track towards the original treatment goal.
Depending on the variables affecting your treatment, you may be able to get the teeth back on track without a revision. Here are some articles covering possible solutions:
Overcorrection is especially likely to be needed for these types of movement:
- Rotations (particularly single-rooted teeth with roots that have a circular cross-section)
- Labial-lingual alignment (particularly of incisors)
- Extrusion (because the PDL tends to pull the tooth back into the socket)
If your case involves any of these movements, requesting overcorrection when you submit the case can help you acheive your desired treatment goals.
For example, on a case requiring rotations, the doctor could add a note to the case submission form asking for the rotations to be corrected towards the beginning of treatment, and requesting overcorrection to further assist with the rotations.
We hope this information helps you to account for the inevitable variables that can affect clear aligner treatment to achieve the treatment outcomes you and your patients desire.