3D Printing in 4 Dimensions

The first-known dental laboratory material to utilize 4D printing is Dentsply Sirona's Lucitone Digital Print 3D Denture resin, which the manufacturer calls a "Body Activated Material (BAM)." The material features "smart polymer technology" that permits the finished denture to immediately respond to body temperature; the work of fracture value increases from approximately 1,500 J/m² at room temperature (25°C) to more than 3,000 J/m² at body temperature (37°C), according to Dentsply Sirona. According to as-yet-unpublished independent research from Boston University that was provided to Inside Dental Technology by Russell Giordano, DMD, the work of fracture value approximately doubles (though the numbers were slightly different) and the material's fracture toughness increases from 2.86 MPa.m^0.5 ±0.24 at room temperature to 3.68 MPa.m^0.5 ±0.20 at body temperature. Conventional and milled denture materials in the study exhibited increases in fracture toughness and work of fracture also, but not as dramatic. These amplified material properties in the printed material help achieve a balance between flexural strength and work of fracture to resist breakage and prevent the worsening of any existing cracks or fractures. Earlier printable denture resins were very brittle and did not have sufficient modulus of elasticity, but with the 4D properties, even if the denture fractures, that crack likely will not propagate. This also allows the denture to be repairable, which is unique at this time for printable denture materials.

In other industries, concepts being explored include self-assembly; products such as furniture hypothetically could be printed and transported in one form and then transform into something different when placed in water, subjected to magnetic energy, etc. Massachusetts Institute of Technology (MIT) researcher Skylar Tibbits, who has been working with 3D printing manufacturer Stratasys, speculates about constructing pipes that could expand or contract based on their contact with water.

While something like that might be far off for dental restorations, the Lucitone Digital Print 3D Denture material offers a glimpse of what could be possible for other dental materials in the near future. For example, a splint material that gets stronger when placed in the mouth could be significant. Brittleness has been a major problem with printed splints, to the point that some dentists provide patients with three copies to prepare for inevitable breaks. Extra strength when the splint is in the mouth can be very helpful, especially at night, when bruxism is often an issue. As we have seen with new materials such as Keystone Industries' Keysplint Soft, combining that strength with flexibility provides the best of both worlds. Being able to print a resin that is as rugged as a conventional splint or night guard but then remains comfortable for the patient is a major benefit, and the time saved printing is great.

Robert Kreyer, CDT, who has worked extensively with the Lucitone material, says there are various other applications possible for 4D printing. "I would like to see teeth that self-occlude," Kreyer says. "Materials that self-equilibrate under pressure. Materials utilizing nanotechnology to adapt to the oral environment, so as residual ridge resorption occurs, the material adapts and eliminates the need for relining. I also envision 4D printing being used for the delivery of certain medications through prosthetics." Kreyer says this is the wave of the future. "We are just seeing the tip of it right now. Smart polymers are the direction we need to go, and utilizing technologies that eliminate the need to manually adjust the products and give the patient a prosthesis that is made for their body, conforms to it, and is activated by it. Within 10 years, this will be the norm."

Being able to print these types of materials is truly remarkable and can make life a lot easier for technicians while being just as rewarding for the patients. Ultimately, giving someone an appliance that will make them feel better about their smile or relieving them from pain is why we do what we do.

Watch a video interview with Kevin Reck about the potential for 3D printing in four dimensions: insidedentaltech.com/idt1199