Repairing an Intraoral Scan with Meshmixer

Your intraoral scanner can record great detail about the area it sees, but it doesn't save any depth data or close-off the edges of your scan. We need to use another program to clean up the model and prepare it for printing. 

There are a few free and premium tools available to repair and add a base to your intraoral scans for printing. Our current favorite free option is a program called MeshMixer. You can find a full guide to using MeshMixer on their website here. In this guide we will go over a basic workflow to repair a typical scan. 

Building a Full Model

This is how most scans will look when imported to RayWare: jagged along the edges and no depth in the 3d rendering of the scan. It is important to understand that proper STL models have to be "watertight" - meaning that all surfaces of the model connect to another surface with no undefined holes/edges. When you see an area with a striped pink or black pattern, that's meshmixer telling you that you're looking at the backside of a model as opposed to a surface of it - you should never see this shading on models that are ready to print. 

In RayWare you can easily spot models like this because the area that is shaded in MeshmMixer is see-through or black (see below). Rayware 2.x versions will show a thumbs down when it detects unrepaired or damaged scans being imported. 

mceclip0.png

There are several similar workflows you can use to repair these models. Here I am going to explain the simplest method that works on the most popular scanners we see on the market (Trios, Itero, Carestream, Cerec, etc., all will work with this method). There are great resources on Youtube and Facebook to see workflows others have developed.

Using Meshmixer

If this is your first time using Meshmixer we will want to hide the print-bed so you can get full spherical rotation around the model. Press CTRL+SHIFT+P to hide the print bed from the workspace. Right Click+Drag to rotate the camera around the object, hold the Middle Mouse Button+Drag to pan and recenter the camera. Take note of the square at the top right corner of the window - use this as a reference to know what perspective you are looking at the model from. 

Different Scanners will export your scans at different orientations. Most scanners will default to saving your files either in occlusion or with both arches teeth up. We think it is much easier to always edit with teeth up then using a slightly different workflow for our uppers & lowers. 

First, let's go to Edit > Transform. Use this tool to rotate the model around so that the teeth are facing up and are level to the reference plane. 

Now we want to go to Edit > Plane Cut - this brings up a flat plane to use as a cutting tool against your model. Sometimes by default the increments this wants to move in are too large - press the up/down arrows on your keyboard while this tool is selected to change adjust the granularity in the movements of the cutting tool. The fatter blue arrow reverses the cutting direction. Press accept to make the change. Cut away anything that is not necessary for the functionality of this model.

Next, click the Select button from the tab on the left. Toggle the tool at the top from Brush to Lasso and use your cursor to circle any areas you would like to select. Press Delete/Backspace to trim the selected areas.

  

With some scanners, we may still see many blue areas indicating holes (areas that the scanner missed). We need to close these defects before moving onto the next step. 

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To close these holes, go to the left part of the screen and select Analysis>Inspectorthe inspector tool will create bubbles attached to each found defect in the model. You need to click all bubbles other than the one that is connected to the greater boundary of the entire scan (the larger the hole the longer it will take to process). Once there is only that one blue bubble remaining we can move on to the later steps of the process. 

 

After trimming all the excess parts and completing small repairs, we press CTRL+A to select the entire model. It will turn orange when selected and a new tab will pop up. Press B to bring up the Smooth Boundary Tool and accept the default settings. Then press D to bring up the extrusion tab. 

In this extrustion tab we want to set offset to -8mm . We also must change the Direction to Y Axis and the EndType to Flat. If you did not orient your model teeth up like we did at the beginning you will run into problems at this step - if after putting in the settings above you have an all black striped model instead of orange go back and make sure you have the model oriented correctly. The orange area must descend below the blue line. If not you must use a value lower than -8, we often need somewhere between -11 to -15 if we are prepping for something like a retainer where we have the full palette in the scan. 

The final step is to use MeshMixer's built-in repair tool to be sure there are no remaining defects in the file. Go to Analysis>Inspector and press Auto Repair All. Then you can export the file in the binary .STL format and open it in RayWare!

We can help with that!

If you're experiencing difficulties or have questions about any of your SprintRay products, submit a support ticket or contact us at 800-914-8004

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