EM "Trying to add a facet to an edge as "left/right", but "left/right" facet already exists"

This error usually appears when opening an order with Dental System Model Builder, or during certain design workflow steps, particularly after defining the margin lines during the segmentation step.
The Dental System software uses various algorithms to read the 3D model and identify basic features such as differentiating teeth and gingiva or determining spatial orientation.

The "facet already exists" error means that the algorithms are not reading the model correctly and are unable to set the coordinates (hence it tries to "add" two left or right sides). Because of this, the specific root cause can vary, but most of the time it involves poor scan quality or design errors related to incorrect margin lines or trimming.

Accordingly, the resolution can be:

1. Searching the scans for any holes or artifacts. These issues can be fixed by using the "Refine Scan" tool in the Prepare step.

You may select all available refine options (Remove scan artifacts, Close holes, Improve scan borders).
Sometimes, you may get a warning that the scan borders cannot be improved—in that case, uncheck the "Improve scan borders" option.

2. Redrawing the margin lines.
Self-intersections or irregularly drawn margin lines in the segmentation step can also cause the error message to appear.

This can be done using the "Edit Lines" tool in the bottom-left panel.

Lines can be redrawn manually for each individual tooth using the "Draw Line" tool, or automatically using the "Clear current tooth spline and rebuild" option, then clicking on the occlusal area of a tooth.

If none of the above work, it could also be due to tooth annotations being set incorrectly, which may indirectly affect margin lines during segmentation—especially if there are annotations in spots where teeth are absent or if tooth numbering has been configured incorrectly.

You can see an example below:

A good way to confirm whether scan quality is the root cause is to replicate the error in your system by exporting the order and/or scans and reimporting them into your own Dental Manager.

If you can successfully replicate it in your system, this can confirm that the most likely root cause is indeed scan quality.

As a last resort, it may be necessary to ask the customer to rescan and redesign the order or use a third-party application of their choosing to improve scan quality.