I realize for many, the integration of a 3D printer seems like buying a novelty item that will sit in the back of the office. Unless good uses are found for this equipment, that just may be true. Purchasing a 3D printer has the potential to gain office efficiencies, improve patient experience, and gain a healthy return on investment.

In order to see these benefits, it is important to develop workflows that maximize the benefits of this technology. To leverage this digital space, consider…

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Selecting the Appropriate Resin

For a 3D printer to be useful to your orthodontic practice, it needs to be capable of producing dental models, appliances, and other essential objects. Thus, you’ll need the right resin materials on hand for your fancy new printer to do it’s job effectively.

The important thing to understand is that resins are custom formulated and printer specific, so you can’t exactly use a generic resin and resins typically cannot be used between different brands of printers, though there are occasional exceptions. Manufacturers will also have a number of different resin options for orthodontists to select from, and you’ll have to choose different resins based on the desired print resolution, print color, and whether or not the resin material should be bio-compatible. Selecting the appropriate resin for the job comes down to how the prints will end up being used.

Resins for Orthodontic Models

When it comes to selecting a print resolution for orthodontic models, and in turn the appropriate resin for that resolution, 100microns is more than enough detail to produce high quality models for diagnostic purposes, retainers, or other appliances. You can always choose to print at a higher resolutions if you desire, it will just take a lot more time to print. When submitting printed models for board ABO board certification, it is recommended by the ABO that you submit the highest quality prints (<30micron resolution) for grading.

Naturally, printed orthodontic models turn out best when they are printed using an opaque material, so it is easy to see fine details across the models. Most 3D printer manufacturers in the dental space seem to think that we like colors that resemble yellow dental stone, so with many companies you’ll get some form of beige or yellow-stone type resin as an option. With my Juell Flash OC printer we use the taupe colored resin, and both Sean and I prefer the standard grey resin for our Form 2 printers.

Colored resins get their color from pigment particles which have different chemistry than resin, so they won’t dissolve in the material, unlike other components. Particles with similar chemistries like to group up, so one of the potential challenges with using pigmented resins is keeping these particles from clumping together and settling. Depending on the resin formulation and type of printer, some manufacturers are able to insert additives to the resins that will help keep the colored particles separated. Other resins may require you to shake the container before adding resin to the vat, or to stir the vat to prevent settling if the printer has been inactive for some time.

Resins for Indirect Bonding Trays & Occlusal Splints

With the appropriate lab software, 3D printers also allow for orthodontic appliances to be printed directly without having to use a physical model. The same minimum resolution requirement of 100 microns applies with direct printed appliances, though many bio-compatible resins are only designed for printing at higher resolutions. 

It should  be fairly obvious that when printing indirect bonding trays & occlusal splints, we’d want to select a clear resin material, but since you are also printing medical devices in this case, be sure to use a resin that is bio-compatible. Some companies offer a somewhat flexible resin to print indirect bonding trays, but this less accurate and can make full seating of the tray less predictable, especially if a team member mishandles the softer tray. In the case of both occlusal splints and indirect bonding trays, you will be better served by printing in a clear, rigid material as in the image below.

Switching Between Resins

Since different resins will be required for different orthodontic indications, another important consideration in purchasing a 3D printer and designing your workflows is how easily you are able to changeover between materials. Some companies like FormLabs, with their cartridge based system and stackable resin tanks, make this process extremely easy, but you may find this difficult with other printers. Top-Down style 3D printers like the Juell Flash OC from Park Dental Research make it especially difficult to change resins, so they are best designed for high capacity printing of a singular material.

The Post-Curing Process

Post-curing, is a light and heat dependent process, that helps 3D prints reach the highest possible strength and become more stable. This additional step to the 3D printing process is an optional step, and should be considered in select applications.  With certain printers, such as the Form 2, printing study models with standard resins does not need this step for most orthodontic uses like vacuum form retainers and diagnostic models.  Post-curing is particularly important for ‘functional’ resins, which in orthodontics would qualify as occlusal splints, surgical guides, and models that would go in a pressure pot.  Adding a UV post-cure chamber to the printing process will finalize the polymerization process and stabilize the resin’s mechanical properties. Specifically, dental resins double in strength with UV post-curing.

From the Formlabs UV curing comparison study: “using a 405 nm light source during post-cure was superior to an equivalent level of lower wavelength light, such as 365 nm. Post-curing at higher temperatures results in a shorter time to full cure. Additionally, higher temperatures lead to higher mechanical properties.”

Post-Cure Hardware

Depending on the size and volume of the appliances or models you are manufacturing, you can consider different types of post-cure hardware. For smaller prints, a low cost 36W nail salon or crafting curing chamber works well.  There are post-curing accessories available from Envisiontec.  Otherwise, the chamber from Kudo 3d has received the best reviews.

When Do I Need to Use a Biocompatible Resin in Orthodontics?

Biocompatibility is required by the FDA for the manufacture of any ‘medical devices’ that will come into direct contact with the skin or oral tissue. Dental and orthodontic models that are used to fabricate clear aligners, or other appliance do not have to be printed with bio-compatible materials.

Direct printed indirect bonding trays, occlusal splints, denture bases, or other printed items that qualify as a medical devices and will come into direct contact with tissue should be printed using a bio-compatible resin.

Currently, bio-compatible resins for use in orthodontics are manufactured by FormLabs, Stratasys, and Envisiontec just to name a few suppliers.

What Does It Mean for A Resin to be Bio-compatible?

Typical 3D printed materials undergo ASTM International standards testing to evaluate material properties like tensile strength, flexural modulus, etc. However, bio-compatible materials must undergo a completely separate set of tests that are according to ISO standards, which can get expensive very quickly. These tests can cost upwards of $100,000 per resin, depending on the medical or dental indications for the resin.

There may not actually be any material difference between standard resins and bio-compatible resins from the same company; however, to produce medical devices with a resin, for the company be able to assert ‘medical claims,’ and to market directly to the dental and medical market the ISO testing is mandatory.

To be classified as a bio-compatible materials, 3D printed resins will undergo biologic evaluation according to ISO 10993-1: 2009 to address cytotoxicity, genotoxicity, and delayed hypersensitivity, and USP plastic class VI, which includes the test for irritation, acute systemic toxicity and implantation.

Resins may also undergo additional ISO testing for certain material properties pertinent to their intended use. For example, a bio-compatible dental resin might undergo ISO 20795-1:2013 testing, which applies to denture base polymers where the manufacturer might be making advertising claims regarding impact resistance.