Thermoforming Clear Appliances With 3D Printed Models

Move your mouse cursor to the bottom surface of the model, you should see an orange arrow, and click.

This should snap your model flush to the build platform.

If you are printing models directly to the build platform you can skip to the second to last section “Printing Layout”. 

Typically, models printed directly to the platform do not require any support structures or additional steps.

When printing parts directly on the build platform, you might see a printability warning. If the part is snapped down to the build platform as outlined in the above section, it is okay to ignore this error.

Tip: When setting up multiple models you can quickly get them into position by rotating and overlapping the parts. The corner or edge of the build platform can be helpful as a stop.

This technique also works great when using Scan to Model.

Once the models are positioned, view the build from the side. Use the view tools on the top right of PreForm as shown.

Select all the models by clicking and dragging over all the models.

Once selected, rotate the models to near vertical orientation.

Once the models are in their desired orientation, add supports.

For jobs where supports are needed, like vertical models, open the Supports tool (see 1) on the left side of PreForm and click the Auto-Generate Selected or Auto-Generate All button (see 2).

Always review, and where needed, edit supports touch points after generation to ensure none are on critical anatomy.

Note: Uncheck the Internal Supports button (see 3) to prevent the generation of some unnecessary support structures.

If a support point is not in an ideal location, you can edit their position.

To edit supports click the “Edit…” button.

Once in edit mode click on a support touchpoint sphere to remove it and click on areas without supports to add touchpoints, if additional are needed.

PreForm will indicate in red which areas might require additional support.

Tip: To quickly remove multiple support points from anatomy click and drag and release across the points you want to remove and hit the delete key on your keyboard.

One of the advantages of orienting models not completely vertical is that support points on critical anatomy are  normally not needed.

Supports might still be generated in those areas. If they are, they can be removed. 

Confirm under the Job Info menu bar on the right side of the screen that Printability shows a green thumbs up.

Whether you are printing on support structures or directly on the build platform, position the parts so they are not overlapping each other. Overlapping parts will be outlined in red.

To rotate the part while it is selected, click-and-drag the outer edge of the orientation sphere.

To move the part, click-and-drag anywhere on the part.

Note: Overlapping the support raft is recommended.

When maximizing the amount of parts on a build move the models as close to each other as possible. 

Always make sure support structures from one model are not touching parts of another model. 

To check for issues. rotate the view and make move models when needed.

Once layout is complete, the job is ready to send to the printer.

Tip: For parts printed directly on the build platform, when positioning models so that the pry point is facing toward the outside of the build platform. This will simplify part removal once printed.

Send the job to the printer by clicking the orange printer icon on the left side of the screen.

The Print dialog box will open, here you can change the printer the job is being sent to (see 1), rename the job (optional, will take use name of file if saved), and send the job to the printer using the Upload Job (see 2) button.

Use a razor blade or sharp scraping tool to work around and under the model. Apply light but constant force on multiple parts of the model's edge.

Tip: When safely used, razor blade scrapers can be extremely effective in removing models from the build platform.

Replacement blades are perfectly sharp and very affordable. Much less force is needed with a sharp blade to easily get between the model and build platform.

Blade holder

Replacement blades

Be sure to have the blade or scraping tool flush to the build platform.

If the process is too difficult or if the blade or part gets damaged:

• The blade is not completely under the model

• The blade should be replaced or sharpened 

• Too much force is being applied in one area of the model, work around the perimeter

For models on supports, insert the scraping tool under the edge of the support raft, apply an even and constant force, and gently twist to pop the part off of the build plate. 

Applying this technique in multiple locations around the raft may be needed.

Remove parts from IPA and leave to air dry at room temperature in a well-ventilated area for about 10 minutes.

Tip: Compressed air can be used to help dry parts, remove trapped resin from small spaces, and allow for rapid inspection of unwashed resin. 

Still, allow for a few minutes of bench drying if using compressed air.

Inspect printed parts to ensure that parts are clean and dry. 

Ensure no residual alcohol, excess liquid resin, or residue particles must remain on the surface before proceeding to subsequent steps.

If any wet, uncured resin is still present after drying, use a squeeze bottle or submerge the part in clean IPA for about a minute, then air dry the parts again. 

Again, use of compressed air allows for rapid inspection.

If supports were used, remove the supports using the clippers provided in the Formlabs Finish Kit, scissors, or other trimming tools.

Tip: While ripping the supports from the part might be quicker, it can leave divots in the part or damage the model. We recommend cutting the supports where connected to critical anatomy off individually.

Vacuum formers pull the material over the model with negative pressure.

Pros

• Affordable

• No compressed air needed

• Simple machine

Cons

• Device quality can be unreliable

• Pressure forming is superior

• Depending on unit, 3D printed models can be a challenge compared to gypsum models

Pressure formers push the material over the model with positive pressure.

Pros

• Excellent fitment around models

• High quality machines

• Some units have automated control; preset programs and pressure release

Cons

• Expensive

• Requires clean, dry, compressed air (up to 90 psi or 6.2 bar)

Tip: Formlabs recommends a pressure former for most orthodontic appliance production. Some pressure formers to consider are Dentsply Drufomat, Great Lakes MiniSTAR, and Erkodent.

Inspect models before thermoforming.

Models that are not completely washed and UV cured can adhere to the thermoforming material.

Unwashed resin will be shiny in appearance and tacky to the touch. 

Resin is more difficult to wash from divots and negative features like engraving.

Thermoformers warm up as they are used and can change heating times. Running a handful of warm up cycles before thermoforming will add consistency to the process.

Depending on the heating cycle, thickness and brand of the material results may vary. 

In testing we found after pressure forming materials 1 mm in thickness resulted in an appliance of ~0.7 mm (see 2).

We also noticed appliance thickness variation in thermoforming models of different heights. In testing models 20 mm tall produced ~0.100 mm thinner appliances when compared to a 13 mm model (see 1).

Having controlled CAD outputs can help keep thermoforming consistent; another option is to use pellets or beads to approximate equal heights during thermoforming. 

The dental pressure formers recommended in the above section have this capability.

Start by removing the model from the sheet of plastic.

Make the initial rough cut by using durable scissors or shears (see 1).

Cut around the bottom of the model (see 2), freeing the outer plastic from the part.

Use a dental low speed cutting disc or wheel to cut the back corner of the plastic away (see 3). 

Be sure to leave enough material around the rearmost molar to meet specifications.

Using a pry tool, work under and between the model and thermoformed sheet (see 4).

Work and lift towards the anterior of the arch.

Using sharp, high quality iris scissors trim the appliance to the desired cervical distance.

Working slowly and carefully in this stage can produce the finished appliance.

Tip: Curved scissors can help on the lingual side of the appliance.

Perform a quality control check to confirm the appliance is complete.

Tip: There are many ways to finish thermoformed retainers and aligners. Thermoforming materials can cut and finish differently by brand and thickness. Choose what technique works best for the material and you.
 

Rough cut the appliance with a cutting disc directly on the model using a low speed rotary wheel.

While this process can be quicker than others it becomes a messier process and requires bench suction and/or use of a respirator to be safe.

A fluted cone or barrel shaped rotary can help finish down tight corners and rough edges. 

This can be helpful if producing appliances that meet the cervical margin and papila.

When cutting or trimming with a dental handpiece it can create flashing and rough edges.

A “deburring” wheel or rotary can be used to finish the edges of the appliance.