How much can we distalise with aligners?

We are all attracted to the concepts of "predictability" or "reliability". We want to offer the best guarantees to our patients in everything we do (and, incidentally, to sleep soundly), but, fortunately or unfortunately, biology is not as exact a science as mathematics.

As we have already discussed on other occasions, the development of aligners opened new doors for the correction of sagittal problems, one of them being the sequential distalisation.

Distalisation is not an easy movement to achieve. Traditionally, appliances such as pendulums or extraoral anchors were used to ensure that the forces applied were sufficiently effective to achieve distal movement of the molars, affecting the anterior teeth as little as possible. These appliances work very well, but they are uncomfortable and are not as easily affordable for today's patient profile. This is why the alternative of aligners is so attractive.

But before we start distalising, it is important to understand how the programmed movements are expressed or, in other words, what percentage of predictability our ClinChecks or Approvers will have.

There are a multitude of studies that analyse the predictability but today we are going to review one published by Safi et al. in which they analyse, by superimposing digital models (using the palatal rugae as a reference), the difference between the planned results and those obtained in the patient after treatment with aligners.

The palatal ridge area is a relatively stable and reproducible structure on the dental model that can be used for registration and superimposition of serial jaw models in aligner treatments. This area is formed by the tissue "ridges" located in the anterior part of the hard palate, which are unique for each individual and can serve as reliable landmarks. This method of analysis allows the initial models to be reliably superimposed on the final phase models, allowing the amount of tooth movement during treatment to be accurately assessed.

The results of the study showed that the planned upper molar distalisation values on the Clincheck were significantly higher than the values achieved in the patient's mouth. The results are shown in the following table:

There are many factors that can contribute to these differences, such as improper sequencing, non-use of attachments or loss of anchorage that occurs in the anterior teeth when attempting to distalise the molars.

This study provides us with interesting information by using a very reliable measurement method. The findings suggest that the planned millimetres of molar distalisation in the Clincheck may overestimate the actual results. What do we learn from these results? That we should be aware of this when planning our aligner treatments.

Knowing these results, we have to optimising treatments to achieve the greatest possible predictability in these movements. Here are a few tips:

• Use shortcuts and IPR to facilitate movements and reduce the need for refinements.
• Use all the 3D tools at our disposal, such as intraoral scans and related software, to assess treatment progress and outcomes more efficiently and accurately.
• Consider individual patient characteristics, such as the amount of space available distal to the second molar, Spee's curve or facial biotype to determine the feasibility and expected results of molar distalisation with aligners.

Saif BS et al. Efficiency evaluation of maxillary molar distalization using Invisalign based on palatal rugae registration. Am J Orthod Dentofacial Orthop 2022;161:e372-e379