The Next Additive Steps

Michael Idacavage, PhD: There is such a wide range of materials. Some are more novelty. Some, like metals, are useful but not very versatile. The inroads being made with plastics, however, are really impressive. You can vary the performance of plastics to be hard, soft, or flexible. You can fine-tune those properties. For dentistry, that means restorations that are not only hard but have flexibility to act like the biomaterial they are replacing. The newest DLP and SLA printers are exciting as well; they give scientists a bigger palette to modify the performance of the materials for dental applications.

IDT: What specific developments on the hardware side are most noteworthy?

Idacavage: Some of the top printers currently in use make it possible to dramatically increase the speed of the printing and print large quantities. In the near future, another technology will be returning to the forefront: inkjet printing, which will expand the possibilities with multi-coloring to include very specific shades, gradients, etc. Inkjet has been limited in the past because of the chemistry: the viscosity of the resins must be low enough to go through the inkjet system. In recent years, however, some really cool advances in the chemistry have allowed inkjet to mimic DLP-type printing. Materials may be commercialized in the next year that could make a really game-changing impact.

IDT: How about functionally: What challenges are posed when printing products for long-term use in the oral environment?

Idacavage: There are challenges, especially with plastics, because you can get small, unreactive materials. One challenge is to make sure everything is reacted, and that nothing can migrate out and potentially cause a problem with a patient down the line. Fortunately, the science has been examined for many years in other industries, such as food packaging, which involves potential moist environments and the risk of affecting people if there are problems. Additionally, the basic chemistry for DLP or potentially inkjet materials is very similar to the composites that have been used in direct restorative dentistry for many years. In some cases, the additive manufacturing resins and the direct composite resins are literally coming out of the same barrel. Instead of curing in the tooth cavity, they are being cured in a vat. Because of those common denominators, there is confidence that these materials can be safe for long-term use in the mouth. Still, as new materials continue to be developed, they need to be thoroughly researched to ensure that there are no problems, and I have definitely observed sensitivity to that among everyone I see working on these materials.

IDT: Along those lines, everyone wants to know about printing zirconia. The stumbling block has been the post-processing. Where does that stand?

Idacavage: That is being looked at quite a bit, but sintering presents some very big challenges and limitations. If I had a crystal ball, I would bet that additive manufacturing eventually will focus instead on materials that are much easier to process but provide similar properties. If a polymer that does not contain ceramic powder can be improved to the point where it matches the performance of zirconia with only a few minutes under a UV light or perhaps a short time in an oven at 120°, that is more likely to succeed. Zirconia obviously has inherent properties that are attractive, but the chemistry is problematic, and if you change that, then you change how the material performs. Trying to make a material that acts just like zirconia but does not need to be processed like zirconia is like trying to have your cake and eat it, too, so the best option is likely to develop an alternative material.

IDT: What other developments should we watch?

Idacavage: Something that is getting a lot of attention in the industrial 3D printing/additive manufacturing world is the ability to use renewable, bio-based, or sustainable sources for these materials. For many years, this was seen as interesting but not important, but in the past year, the green movement has gained momentum. I know of at least one bio-based material being developed for dentistry that may be released next year. The whole green movement may carry over to dentistry soon, with people asking where these materials come from.