Behind the Resin: Developing FP3D for Flexible Removable Printed Dentures

In the world of digital dentistry, clinicians and labs have dreamed of a way to print flexible partial dentures—something that could stand up to everyday use, fit comfortably in the mouth, and meet aesthetic as well as rigorous mechanical demands. With the launch of FP3D^™ resin, that wish is now a reality. This flexible, dual-cure resin is the result of a close collaboration between Carbon and Keystone Industries, combining materials science expertise and regulatory experience to fill this gap in the dental market.

A Clear Need and a Longstanding Partnership

The journey toward FP3D began, as many innovations do, by listening. In regular surveys and customer conversations, Carbon repeatedly heard the same request: we want to print flexible partials. Labs wanted a printable option because the traditional methods of creating these partials are low-throughput and extremely labor-intensive.

Carbon and Keystone already had a strong partnership to build on, and the two companies shared a common vision for what digital dentistry could become. They expanded this relationship through an announcement in September 2021, stating their plan to form a cross-functional team of materials scientists, characterization specialists, print development teams, and regulatory experts to bring FP3D to life. This was a true joint effort from the ground up, leveraging Carbon’s proprietary dual-cure chemistry and combining that with Keystone’s regulatory and industry expertise.

Finding the Formula

Designing a material that could match or outperform incumbent flexible materials wasn’t simple. There were over 100 product requirements to meet before the teams were comfortable bringing this resin to market. Some of those requirements included:

• FDA-cleared Class II Medical Device
• Durability that surpasses a 3-year lifetime of insertion and removal
• Excellent chemical retention of teeth
• Natural aesthetics with high translucency, ensuring a seamless blend when placed intraorally
• Easy integration with existing digital dentures workflows
• Enhanced polishability compared to thermoplastics
• Improved economics compared to traditional fabrication methods
• High precision and accuracy for increased intraoral retention and comfort

Dual-Cure Chemistry: Power + Precision

From the start, the team suspected that Carbon’s dual-cure technology (a chemistry that lends itself to extremely high durability without sacrificing print speed, precision, or economics) would be essential. Despite this, the team knew single-cure workflows would be simpler for labs, so they conducted extensive testing to try to find a single-cure solution. However, the testing proved these single-cure versions couldn’t stand up to the strain of daily use.

Using Carbon’s proprietary rigid polyurethane (RPU) chemistry as a base, the team engineered a UV-curable formulation that printed accurately, and included a thermally activated structure that delivered the needed stiffness and durability. After more than 100 iterations, they optimized a formulation that delivered the right performance and simplified the ingredient list.

Focus on Accuracy

The biggest technical challenge was maintaining accuracy throughout the entire workflow. Because partials fit around remaining teeth, even small deviations can compromise the fit and lead to patient discomfort.

During thermal curing, printed parts can warp or droop under heat. To preserve precision, the team added a salt bake to the workflow. The salt bake encases the parts in a fine-grained, water-soluble salt that provides temporary structural support during the thermal cure. It’s an inexpensive and elegant solution—one that ensures the accuracy clinicians demand for a proper fit.

Ensuring the dual-cure chemistry, salt bake, and print parameters all worked together seamlessly to yield accurate parts was the most time-consuming and most important part of the project.

Testing, Customer Feedback, and Final Tweaks

Throughout development, the team rigorously tested both component and full-product performance. That included:

• ISO testing to ensure key mechanicals were met, such as Flexural Modulus and Work of Fracture
• Cyclic fatigue testing to ensure durability
• Biocompatibility
• Comparisons to other flexible milled materials to benchmark success

The team found that FP3D performed quite well across all required tests, but particularly in the mechanical and strain testing. It withstood repeated stress past the 3-year benchmark, which no other 3D-printed resin on the market is able to surpass.

While the FP3D team members aren’t partial denture design experts, their customers are, and customer-designed models were critical for validating performance with representative geometries. So, while performing their tests, the team sent printed samples to select lab partners to get feedback on thickness, translucency, and color shades. This feedback loop helped fine-tune the material’s aesthetic range and recommended minimum thicknesses.

From a materials science perspective, durability, elongation at break, and cyclic fatigue are the standout technical achievements of FP3D, but labs have also noted a practical and unexpected benefit: polishability. Unlike some flexible materials that gum up polishing burrs, FP3D flakes off cleanly, behaving like traditional acrylic and making device finishing faster and easier.

Just the Beginning

With FDA clearance in hand, Carbon and Keystone turn their focus to European regulatory approvals. In addition, the success of FP3D and lab adoption of a dual-cure workflow opens up possibilities for other dual-cure resins in the dental space.

FP3D isn’t just a new material; it’s setting a new standard for performance in the category of digital dental appliances. By combining comfort, durability, and digital efficiency, Carbon and Keystone have delivered a long-awaited solution to a persistent customer need. The era of direct printed flexible partial dentures has begun.