How does resin polymerization work in dental 3D printing?

What you will learn about dental polymerization and 3D printing:

• What is 3D printing resin?
• What is polymerization in 3D printing?
• Postprocessing Advances in Digital Dentistry
• Key relationships

In today’s world of dentistry, it is almost impossible to get the terms 3D printing and digital out of the picture. Additive manufacturing – otherwise known as 3D printing – is revolutionizing the industry. Its speed, accuracy and affordability make it an increasingly popular choice among dentists and lab technicians who want to prioritize these in their practice or lab. of Accuretta SOL is just one example of a printer that makes printing easier, faster, and more accessible to anyone—whether with splints, surgical guides, prostheses, or anything in between.

3D printing has been around for over 40 years, but has grown exponentially in the last 10 years and is projected to continue to grow. Today there are approximately 230 dental 3D printers manufactured by more than 75 companies worldwide.¹ The global dental 3D printing market is estimated at approximately $3.2 billion in revenue.² and is projected to grow to $9.5 billion by 2027.³ This technology has revolutionized manufacturing ranging from the medical, dental and aerospace industries to the culinary and automotive fields.

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While there are many different printing technologies on the market, those used in the digital dental field include stereolithography (SLA), digital light processing (DLP), and liquid crystal display (LCD) in both RGB and monochrome. All these methods use liquid resin as the material from which the prints are made. Through the polymerization process, the resin is transformed from a liquid to a solid and after processing it results in a print that is both durable and biocompatible.

You may be familiar with the different steps in a digital workflow, but to learn more, take a look at the step-by-step process. The technology that turns liquid resin into a solid print is less well known, but the innovation behind it is fascinating. To understand this polymerization process, we need to know more about the resin material itself.

What is 3D printing resin?

Resin is a substance that can be produced naturally or synthetically and consists of different components depending on its use and function. It’s the material used in dental 3D printing for everything from models to dentures to surgical guides. While known simply as “resin” or “material” in the 3D printing world, it can also be referred to as polymer resin, resin-based compound (RBC), or photosensitive resin. Resins on the market are differentiated based on their composition, which is a combination of monomers, crosslinkers, fillers (for example, ceramics in the case of permanent resin), pigments and other chemical components. These components and their proportional amounts determine the accuracy, print performance, biocompatibility, mechanical properties and other elements of the final print you are trying to achieve. All 3D printing dental resins (and photopolymer resins in general) must have at least one monomer⁴ (which is the main component), a crosslinker and a photoinitiator (which reacts when it comes into contact with UV light).

Before composite resins, other materials were used in dental applications, especially in terms of fillings: gold, then concrete and dental amalgam.⁵ The 1950s and 1960s saw the formulation of the first composite resins and the emergence of the term “composite” in dentistry, which was previously known as “reinforced”.

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The range of resins available on the market is growing all the time, and therein lies the potential of 3D printing. The number of applications that can be printed is expanding. Companies are currently working on creating a resin to print reliable aligners at home, which would be a game changer for the industry – and the speed at which it can be done is also increasing. It is possible to print a crown and place it in the patient’s mouth within an hour.

Polymerization is the next step.

What is polymerization in 3D printing?

Polymerization is the chemical process of turning the resin from a liquid to a solid, through the formation of chemical bonds between the resin molecules. During printing, a pot of photopolymer resin is placed in front of a UV light source (for example, an LCD screen). The monochrome (or in some cases RGB) LCD display allows UV light to be emitted in a specific pattern; the resin only cures in specific areas that come into contact with the light. Each layer is printed in the specific pattern in which the light is emitted.

3 stages of polymerization

The polymerization process occurs in three stages: initiation, propagation and termination.

IN initiation phase, a catalyst (in this case, UV light) starts a reaction with the photoinitiator, which releases a free radical. Photoinitiators release these free radicals at specific wavelengths of that light source. This is what starts the polymerization process.

The free radical binds to a monomer and opens the double bond, which starts a chain reaction. The double bond of one monomer is opened, which then binds to another monomer opening its double bond, which binds to another monomer, and so on. This process is known as the spreading phase. More monomers are linked together, creating long chains of molecules called polymers.

of completion stage occurs when two long chains—each with an open monomer at one end—link together, forming a long chain. In other words, when the last free radical in one chain meets the last free radical in another chain, they combine and the process ends. This long polymer chain is one of many that make up the solid print.

Note: In 3D printing with an LCD screen (such as the Ackuretta SOL and DENTIQ), the print resolution is determined by the size of a single pixel. In SLA (with a laser), the size of the laser determines that definition. DLP resolution is based on the definition of the projected image. Additionally, higher resolution does not equal longer print times.

Polymerization process

1. The liquid resin is poured into the pot or
2. A 3D model is created using CAD software, and then divided into multiple layers using software such as ALPHA AI.
3. The 3D printer uses UV light via an LCD screen or laser to selectively cure the resin in the model corresponding to each layer of the 3D design.
4. The build platform is lowered and then raised as each layer dries, allowing the next layer of liquid resin to be exposed and cured on top of the previous layer.
5. This process is repeated for each layer of the 3D print until the entire product is made

The result of this photopolymerization process is a solid object made of cured resin, which must then undergo post-processing to ensure it is fully cured and biocompatible. This is especially important for applications that will be in the patient’s mouth for a long time, such as splints, crowns and dentures.

Postprocessing Advances in Digital Dentistry

Once your print is finished printing, post-processing steps ensure that the print is fully cured and safe for your patient.

Cleaning: The cleaning step—which is performed with either ethyl alcohol or isopropyl alcohol (IPA)—removes any raw resin from the print and any polymer that has dried but not fixed to the print. While cleaning is not part of the polymerization process, it is a necessary step to provide the patient or clinician with a safe, high-quality end result. A dual tank cleaning unit (such as CLEANI) is an ideal tool for this step.

Cure: Curing is the last step of the process which is carried out with the help of a UV curing oven (such as CURIE or CURIE Plus). This ensures that all expected polymerizations are complete.⁶ Overloading can occur if there is an excess amount of reaction, which can cause more polymerization reactions, cross-linking reactions, or unfavorable side reactions than desired.

After your print has been cleaned of all raw resin, place it in a UV curing oven with different wavelengths so that they penetrate the print and complete the polymerization process, ensuring safety and full mechanical properties.

After completing this step, your print is complete and ready for your patient.

Key relationships

• The resin consists of photoinitiators, monomers, crosslinkers, fillers, pigments and other chemical components.
• There are three stages in polymerization: initiation, propagation, and
• Post processing is essential to ensure your print is as consistent and

Definitions

• Monomers: small organic molecules that can form a repeating pattern when covalently bonded to each other.
• Polymers: large molecules composed of smaller monomeric units that are covalently linked in a repeating pattern.
• Polymerization: a process where a large number of monomer molecules react together to form a polymer.

Editor’s note: This article first appeared on Through Loupes newsletter, a publication of the Endeavor Business Media Dental Group. Read more articles and subscribe to Through Loupes.

References

1. Global Dental 3D Printing Sky Research Forecast. https://skyresearchforecast.com/reports/medical-devices
2. Dental 3D Printing Markets and Markets. https://www.marketsandmarkets.com/Market-Reports/dental-3d-printing-market-258228239.html
3. 3D printing: the future of dentistry. Burkhart Dental https://www.burkhartdental.com/3d-printing-the-future-of-dentistry/
4. Portfolio of 3D printing resins from Ackuretta. Accurate. https://ackuretta.com/collections/curo-resins-for-dental-3d-printer
5. Riva YR, Rahman SF. Dental composite resin: a review. AIP Conf Proc. 2019;2193:020011. doi:1063/1.5139331

Additional resources