Understanding Over Correction Trays in Orthodontic Cases

Question

For refinement movement - closing left over gaps, are there any specific instructions we provide to invisalign tech? Like add power chain etc?


Answer

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When finalizing an orthodontic case, it’s essential to ensure that the interproximal contacts are tight, minimizing the risk of food traps between teeth.

Traditional Use of Over Correction Trays

A common method for fine-tuning orthodontic treatment is using over correction trays. By selecting the "Over Correction" tool, either in the software menu or by pressing the "O" key, clinicians can view trays designed for potential over correction at the end of the treatment plan. These trays allow for additional movement of specific teeth to achieve optimal alignment.

For instance, in a scenario where the lower canines started with significant rotation, the clinician might request an additional 0.3 mm of distal movement to fully achieve alignment. However, it’s worth noting that over correction is typically requested after completing the entire aligner series, when additional trays are needed for fine-tuning. These trays focus solely on the over-corrected movement and are distinct from the standard treatment plan.

Over Treatment vs. Over Correction

It’s important to distinguish between "over correction" and "over treatment." Over treatment refers to adjustments incorporated directly into the aligner set, whereas over correction trays are supplementary and appear only after the initial treatment is completed. Although over correction trays are not made of a different material, they are labeled as “over correction aligners” within the software interface.

Virtual C-Chain for Tightening Contacts

Clinicians often request a "virtual C-chain" to help close gaps between teeth, typically for the 3-to-3 (canine to canine) or 6-to-6 (first molar to first molar) regions. This approach forces all the teeth together without differentiating between specific teeth, which can sometimes lead to overly tight contacts or even slight crowding or intrusion. As a protocol, many practices opt to ensure appropriate spacing between contacts by asking technicians to simulate Interproximal Reduction (IPR), rather than physically tightening the contacts.

Interproximal Reduction (IPR) Protocol

The IPR technique helps maintain optimal spacing by virtually reducing tooth structure in small increments. Here’s the standard protocol:

  1. Assess Contact Tightness: Using dental floss, check the contacts between specific teeth. If the contact feels light but is present, plan for 0.2 mm of IPR. For contacts with an air gap that appears visually closed, plan for 0.3 mm of IPR. If space is visibly present, plan for 0.4 mm of IPR.

  2. Planning IPR Without Executing It Physically: It’s critical to remember that the IPR process is only simulated within the treatment plan. This virtual adjustment removes a small amount of tooth structure (up to 0.4 mm) to create space for proper tooth movement, but it does not need to be physically performed. The software simulates tooth reduction, showing the teeth closing the gap as planned.

  3. Specific IPR Instructions to Technicians: The clinician should request that specific IPR measurements be applied in the software. For example:

    • At aligner number one, request 0.3 mm of IPR between teeth 3.6 and 3.7, and 3.6 and 3.5.

    • Request 0.4 mm of IPR between 3.5 and 3.4, 4.3 and 4.4, and 4.5 and 4.6.

    • For lighter adjustments, request 0.2 mm of IPR between 3.3 and 3.2, and 4.1 and 4.2.

All planned IPR should be completed in the software at aligner number one, setting the foundation for effective final alignment.

Summary

In summary, the use of over correction trays and virtual IPR in orthodontics provides a flexible approach to achieving precise alignment and contact tightness. Over correction trays are an optional step following the initial treatment, while virtual IPR ensures effective tooth positioning by planning minimal, controlled tooth structure reduction. Following these protocols allows for high-quality finishing and avoids potential complications from overly tight contacts or unintended tooth crowding.