3D printing aligner models for thermoforming without distortion
How to 3D print aligner models for thermoforming without distortion: resin choice, hollow or solid models, orientation, curing, heat resistance and labeling.
Aligners, retainers, bleaching trays and many splints are thermoformed over a printed model. The model never touches the patient, but every error in it ends up in the appliance that does. A model that softens in the forming machine, swells at the margins or carries a resin film produces an aligner that fits badly. This post covers 3D printing aligner models for thermoforming, with the settings and checks that keep them accurate.
Choosing the resin
Thermoforming heats a plastic sheet and presses it over the model. A general model resin may soften under that heat and deform, so use a model resin whose data sheet states sufficient heat resistance after post-curing for the forming machine in use. Many manufacturers sell resins intended for thermoforming models. Color matters less here than for crown models, but a light, even color makes it easier to see margins and trim lines.
Hollow or solid models
Hollow models print faster and use less resin, which counts when a case has many stages. The walls must be thick enough to withstand the heat and pressure, and the base needs drain holes so resin does not stay trapped inside. Solid models are sturdier and simpler to process. Test the choice with your resin and forming machine before switching a whole production.
Orientation, supports and exposure
Print with the arch oriented so that support marks fall on the base, not on the teeth or the gingival margin where the aligner seals. Flat printing directly on the build plate is common for aligner models and avoids supports altogether, as long as the first layers do not create an enlarged base.
Exposure decides surface accuracy. An over-exposed print has slightly swollen surfaces, which makes the aligner looser. Calibrate exposure for the model resin as described in resin printer exposure calibration.
Washing and post-curing
A film of uncured resin on the model sticks to the sheet, leaves marks and can change the fit. Wash and dry the model thoroughly, then post-cure as the resin instructions state, which also gives the model its full heat resistance. The details and common mistakes are in post-curing dental resins.
Labeling and traceability
Aligner cases have many models that look alike. Embossing the patient code and stage number on the base during design avoids mix-ups at forming and trimming. Most design software can add a label, and in Blender it is a simple modeling task (see Blender for Dental vs exocad).
Checks before thermoforming
Check the model for supports or artifacts on the teeth, for a clean surface without resin film and, on a sample of models, the accuracy against the design. A model that rocks on the forming plate or has a warped base will produce a deformed aligner. The printing side of models in general is covered in exocad Model Creator.
Frequently asked questions
Should aligner models be hollow or solid?
Hollow models print faster and use less resin, but the walls must be thick enough to withstand the heat and pressure of the thermoforming machine, and the base needs drain holes. Solid models are sturdier. The right choice depends on the resin and the forming machine.
Why does the aligner fit loosely although the model looked fine?
Common causes are a model that deformed under the heat of thermoforming, an over-exposed print with swollen surfaces, or uncured resin left on the model. Checking the model against the design and using a resin rated for the forming temperature solves most cases.
Do aligner models need special resin?
They need a model resin that resists the heat of the thermoforming machine without softening. Many manufacturers sell resins intended for thermoforming models, and their data sheets state the heat resistance after post-curing.