The traditional way of creating a physical model of a patient’s dentition from the impression in dental practices and labs is stone modelling.
But there’s no doubt that it’s far faster, cheaper, simpler and cleaner to create physical models via 3D printing. And if you want to fabricate models from IOS scans and digital impressions, then 3D printing is one of the few ways to achieve that. Models don’t need to be stored physically – they can be held as digital files by dental practices and labs instead. And as and when they’re needed, models can be recreated at any time by using the digital file.
Also, 3D printed dental models can be used to fabricate items such as vacuum-formed clear aligners.
There are four simple steps to the 3D printing workflow: scanning, designing, printing, and preparation.
There are many more steps involved in stone modelling, which is overall a far more labour-intensive process. The 3D printing workflow is simplified and therefore more efficient. It is far quicker to carry out an intraoral scan, clean the mesh with CAD software, and send the finished model to a 3D printer than it is to make a cast of a physical impression, prepare a stone mixture, and then pour, clean, and trim a stone model.
Meshmixer is software that is free, yet extremely powerful and is used to clean 3D scans and prepare them for printing. Not only can Meshmixer be used to optimise the mesh, but the dental professional can also resculpt entire sections, stylise the model, and add useful features as desired.
Below, you’ll find a webinar that demonstrates the process in stages in a video tutorial.
Before you start using Meshmixer, it’s beneficial to cover some of the basics.
There are two menus within the software; the first is on the left sidebar, while the second runs along the top of your page. The former is where you’ll find the tools you need to clean your mesh, while the latter is where you’ll look for administrative functions including exporting and saving.
In common with many CAD programs, Meshmixer refers to your 3D model as a mesh. This name is derived from the way the file data is stored, which is as a network of interconnected points that together make up each surface. Whenever this tutorial or the Meshmixer software uses the term ‘mesh’, it means your model.
Our best tips for using Meshmixer include the following:
If you’re in a hurry to produce your model, your mesh can be quickly cleaned by doing the following:
Activate the Select tool by clicking on the relevant button on the left sidebar menu.
Use Control + A on a PC or Command + A on a Mac to highlight the entire mesh.
Navigate to Select → Modify → Smooth Boundary to quickly smooth out any unrefined edges. When you’ve finished, click on Accept.
Ensure your model is still selected, then navigate to Select → Edit → Extrude. There will then be displayed two types of end: Offset and Flat. Alter the end type to Flat to create a smooth bottom that will be easier to work with.
This will apply an external boundary, known as an extrusion, to the mesh. Make sure that the extrusion extends beyond the whole edge of the mesh. You can fix this by dragging the Offset sphere or typing in a negative Offset range to achieve the desired thickness.
Click on Accept, after which the file can then be sent to the printer – click Export to achieve this.
There are two ways to create a more refined, smoother model. These are Plane Cut or Select and Cut. With the Plane Cut function, you can quickly remove any large unrefined sections by undertaking just few simple steps. Select and Cut is a more appropriate method to use if you are working on smaller sections.
Ensure your model is rotated so that the anterior appears at the top while the posterior is located at the bottom, and the unrefined edge of the scan is to the left of your screen. Ensure that the molars are aligned.
Click Edit → Plane Cut.
Draw a vertical line along the edge that’s yet to be refined by clicking and dragging.
Check that the areas of the mesh you want to keep are opaque, but the side you want to remove is transparent. You can use the blue arrow located in the middle of the mesh to switch the sides if you need to.
If you click on Accept, the plane cut function removes the edge that’s been selected.
To refine the model further if required, you can make use of the Select and Cut method.
Once you’re happy with the model, click Select → Modify → Smooth Boundary to smooth the boundary, then click Select → Edit → Extrude to add an extrusion. Once these stages are complete, the model can be exported.
Locate the area to be refined.
Navigate to the Select option, where you’ll spot the Brush Mode option. Select the size of your brush from the menu.
Locate your cursor to a little way away from the side of the mesh, close to the area you want to select. Then hold and drag your mouse to activate the brush and drag it along the area to be cut off.
Release the mouse button close to the area where your brush started. The area you’ve selected will be highlighted in orange.
Hit the Delete button on the keyboard to remove that area. Repeat the process for each of the areas you wish to refine.
Once you have finished refining the model, you can smooth the boundary off by repeating the Select → Modify → Smooth Boundary process. Any extrusions can be added with the Select → Edit → Extrude process. The mesh can now be exported.
While cleaning your image up, you may find there are a few holes in the mesh. These need to be filled before the model is sent for 3D printing.
Here’s how you can achieve this:
You can automatically identify any such holes by navigating through Analysis → Inspector. You can now easily see what holes there are to be filled. These will be indicated by a series of spheres that will direct your attention to any holes in the model. Ignore the hole that appears as the large opening over the perimeter of the impression surface.
One by one, fill in the smaller holes automatically by clicking on each indicating sphere.
Once the process of cleaning the mesh has been completed, the refined model can be uploaded into the 3D printer’s print preparation software to ready it for printing.
Use Formlabs’s PreForm software to convert your 3D intraoral mesh into a printed model. Here’s how :
First, export your model in STL Binary file format from Meshmixer. Then, open it with the PreForm software.
On the left-hand menu, navigate through Orientation → Select Base.
Snap the model onto the build plate by clicking on the bottom.
Drag the models to their desired locations to arrange them for printing on the build plate. To expedite the process, put your models in priority order towards the mixer side of the plate.
Make sure your printer is set up, then click Print. Once printing is complete, the model can be washed, dried, and post-cured, ready for its intended use.
The benefits of 3D printing dental models on-site include reduced costs and faster modelling and processing times. CAD software such as Meshmixer may look complex, but in fact, the learning curve is not at all steep. After a short training session, dentists and other dental professionals will find it easy to get up to speed.
With a Formlabs dental 3D printer, the Scan to Model feature can also be used simply and efficiently to convert intraoral 3D scan files into solid, printable models directly in PreForm.
Would you like to add 3D printing to the menu of services offered by your dental lab or practice? Then all you need are the right tools. Our high-res SLA (stereolithography) 3D printers work with a variety of materials and can help you process intraoral scans into precise printed models suitable for a wide range of indications.
Request a free sample part printed on a Formlabs 3D printer and learn more about the capabilities and performance of SLA 3D printers overall by contacting us today.
