How much can we distalise with aligners?

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

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

The distalisation movement is not an easy task. Traditionally, appliances such as pendulums or extraoral anchorage were used to ensure that the forces applied were effective enough to achieve distal movement of the molars, while affecting the anterior teeth as little as possible. These appliances perform 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 starting to distalise, it is important to understand how the programmed movements are expressed or, in other words, what percentage of predictability our ClinChecks or Approvers are going to have.

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

The palatal rugae 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 treatment. 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 table below:

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

This study provides 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 must optimise the treatments to achieve the greatest possible predictability in these movements. Here are some tips:

• Use attachments and IPR to facilitate movements and reduce the need for refinements.
• Use all available 3D tools, such as intraoral scans and related software, to assess treatment progress and outcomes more efficiently and accurately.
• Take into account individual patient characteristics, such as the amount of space available distal to the second molar, the curve of Spee 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