Expansion by torque change

In the alignment of simple cases, such as this one, we may encounter several challenges, particularly in adult patients who have pre-existing recessions, which must be analyzed in depth to distinguish their origin.
It is important to understand that in these cases a mass expansion would be inadvisable, because it would force more the relationship between the root and the vestibular cortex, while an expansion by torque change, where the apex does not move to vestibular, is feasible from the periodontal point of view, and predictable from the biomechanical point of view.

In the case of a mass expansion, where the apex is displaced like the crown to vestibular, it is necessary to define the force system based on hypercorrection of the radiculo-vestibular torque, pressure areas (G8, Invisalign) on the palatal side and optimized attachments combined with the above,... to achieve a difficult movement.
In addition, in such cases it would be necessary to have a good amount of vestibular bone through which to move the tooth.

 

In the case of a torque shift expansion, where the apex does NOT move vestibularly, it is somewhat simpler, without the need for hypercorrection or a sophisticated system of attachments or pressure areas.

In the case of a torque shift expansion, where the apex does NOT move vestibularly, it is somewhat simpler, without the need for hypercorrection or a sophisticated system of attachments or pressure areas.

 

  • For this, it is important to remember that root movements will be expressed the larger the clinical crown (in premolars it may be the case that they have a reduced size).

In cases where part of the root surface is exposed, we can ask the CAD designer to extend the aligner scalloping 1 or 2 millimeters beyond the cement/enamel junction line (as long as there is no periodontal compromise or excessive retention of the aligner at that level, this should be evaluated on a case-by-case basis). As the distance between the two points of force application increases, this movement becomes more predictable.

 

  • To program this movement, it is convenient to add approximately 5-6 degrees of palatal radicular torque to these pieces for every 1mm of coronal expansion, and instruct the technician to express it simultaneously with the coronal expansion.

The figure of 5-6 degrees is a guideline... we know that it will hardly be expressed, but it is enough to achieve some radiculopalatine movement and not so great as to generate a misalignment.

  • Regarding the total expansion, we define it with the lower arch, which is the one that in this case from the frontal view shows that its pieces are closer to torque 0.

We set as a reference 34 to compress the lower arch with the ARCADA TOOL, going from an initial expansion of the lower arch and the rest to a more limited one.

Then, we ask this tool to COMPLETELY coordinate both arches, in this case taking the lower one as a reference, letting the algorithm save us the work of coordinating tooth by tooth.

When using the ARCADA TOOL we must then thoroughly check the coordination of both, as well as the alignment. This is because the algorithm does an excellent job of coordinating the two, but it is we who must detect small errors, such as excess torque on 23, which causes it to be misaligned: small individual corrections of that type will reduce the number of refinements afterwards.

 

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