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Inside Dentistry

June 2014, Volume 10, Issue 6
Published by AEGIS Communications


3D Printing Technology

Potential To Change The Dental Industry

Kate Hughes

Additive manufacturing, also known as 3D printing, is an emerging technology that has the potential to revolutionize product realization. As one of the fastest growing and most buzzed about technologies in recent years, it allows the layman to realize three-dimensional (3D) product designs without the need for a manufacturer—if you can dream it, you can create it.

With nearly limitless potential applications, 3D printing encourages creativity and enterprise, giving anyone with vision the ability to hold that vision in hand. Parents can create personalized toys for their children, bypassing the manufacturer and traditional retail store. Inventors can print prototypes and test new parts in a matter of hours and at a fraction of the cost, rather than waiting weeks to have them remotely manufactured at great expense. If the faucet in your bathtub breaks, you could print a replacement without the need to visit the hardware store. The possibilities are seemingly endless.

As one of 12 new technologies recognized by the McKinsey Global Institute as a “disruptive technology,” 3D printing has the potential to transform our lives, businesses, and the global economy.1 Already this technology has left footprints on a number of industries, with people printing everything from jewelry and food to clothes, guns, and medical devices. It is the latter application that has garnered the rapt attention of the dental industry. Only a handful of additive manufacturing companies are currently in the dental space, but those bringing the 3D printing movement to dental technology are racing to develop new materials and applications that will expand 3D printing’s role in manufacturing dental devices and eventually be at the forefront of producing long-term end-use restorations.

Why 3D Printing Matters

3D printing technology is still an immature market. Only a small percentage of laboratories in the United States are using 3D printing or sintering technology to efficiently deliver large numbers of structures in a single production cycle. According to Al Siblani, chief executive officer of Envisiontec, Inc., the dental technology industry first began to pay attention to 3D printing when the technology matured to the level that full-contour crown and bridge wax patterns could be produced with stunning amounts of anatomical detail in comparison to those produced by milling. “The anatomy displayed in these 3D printed wax patterns was far superior to anything we had previously been able to achieve,” says Siblani.

It wasn’t just the anatomical detail and timesavings that made 3D printing an attractive alternative to hand waxing. It was cost savings. Once the great potential inherent in additive technologies was realized, larger laboratories and manufacturers adopted the technology to reduce the cost of manufacturing precious metal restorations, especially in light of rising gold prices.

Siblani explains, “In the past, when working on a precious metal full cast crown, a CDT would have to keep adding wax to create that high-end anatomical detail. By using 3D printing, laboratories were able to digitally optimize the thickness and consistency of the wax pattern through the CAD design software thus minimizing the amount of precious metal used in the casting process. In instances like this, switching from a manually produced full anatomical wax pattern to a 3D print-assisted wax pattern saved users a tremendous amount of money.”

From this starting point, additive manufacturing technology has mastered the production of more complex structures, such as partial denture wax patterns, implant surgical guides, and working models, as well as semi- and non-precious copings, titanium implant bars, and even denture bases. Today, 3D printing is generally accepted as an effective technology and offers a vast improvement over the time and resources required if a technician were to manually create or mill these structures instead. This becomes truer as the technology continues to improve. “Now, 3D printing has the ability to deliver a lot of parts in a very short period of time, without putting financial strain on the laboratory. As a whole, 3D printing is a fast, cheap, effective solution that will almost certainly change the dental technology industry greatly in the years to come,” says Siblani.

Avi Cohen, director of global dental for Stratasys, agrees that additive manufacturing technology has great potential but, as with any new technology, 3D printing is in need of a more mature market. However, as the technology matures and the market expands, the next huge frontier for additive manufacturing will be delivering products from the machine that will be directly placed in the mouth. “What I see is a movement, a very serious movement, to the end-user approach,” says Cohen.

Research and development dollars are being spent on developing materials and more advanced technologies that can deliver an end product with the strength and durability to withstand the extreme environment and forces inherent in the human mouth. “There is a great deal of work going on right now,” says Patrick Dunne, applications development engineer at 3D Systems. “Much of it is confidential, but in terms of end product crowns, my feeling is initial developments will be through the photopolymer composite route.”

And that route would first take the form of 3D printed temporaries and then more sophisticated end products says Robin Carden, senior director of research and development at Glidewell. “We have an entire wing of our Research and Development center devoted to additive manufacturing technology and are experimenting with a number of different materials.”

Taking the Next Step

So how far away is research and development from delivering a 3D manufactured full-contour crown? The hurdle will be developing materials that are not only strong enough to withstand a harsh oral environment, but also esthetic enough to meet the high standards of today’s patients. It may be several years until that balance is achieved and a viable material reaches the market. However, Carden believes initial developmental breakthroughs will be realized in the next year or so.

These experts all agree, however, that 3D printed zirconia will not be one of those new material developments. “When you try to mix zirconia powder with materials that would convert it to a flowable form along with binders to solidify the material, the material loses 50% of its density, not to mention the challenge of burning out those binders which results in a massive amount of shrinkage,” says Dunne. “Firing also never quite eliminates the porosity of the material and the carbon contamination caused by the binders trapped in the matrix destroy its mechanical properties.”

Even if an advanced ceramic or zirconia were developed, the challenge as Carden sees it is the ability of the technology to achieve acceptable translucency as well as the required high flexural strength and fracture toughness in the end product. He references a 2009 published study carried out at Aachen University in Germany where researchers, using a modified direct drop-on-demand inkjet-printing unit, produced crowns from a zirconia-based ceramic suspension. “The problem with the resulting crowns was the lack of translucency and the ability to only achieve 763 MPa flexural strength,” explains Carden.

Dunne believes new material developments for producing a 3D machine-to-mouth end product such as a crown will begin with modifying photopolymer materials such as 3M ESPE’s Lava Ultimate composite. “Advanced structured resin-based nano-ceramic material eliminates many of the problems associated with composites in the past,” says Dunne. “It doesn’t dull over time and is color stable, and in terms of mechanical properties is formulated to last 10 years in the mouth but only time will give us the long term conclusions on durability.” Techniques are evolving he says that are capable of 3D print processing composite materials that have been altered into a toothpaste-type viscosity.

Carden agrees that composite materials like Ultimate will be the starting point but takes the vision a step further by envisioning the creation of a hybrid crown composed of polymer composite base deposited by one printing nozzle and a 50/50 mixture of a nano zirconia polymer deposited by a second printing nozzle to add strength to the end product. And if a multiple nozzle technology were developed, it opens the door to printing multiple shades over the base material. “Imagine a main printing nozzle with multiple nozzle arms like an octopus coming down around it,” says Carden. “Each of the arms would be controlled by a computer-controlled gate system to deposit patient-specific shades to the restoration.”

Eventually Carden says advanced 3D technologies will allow the manufacture of end product crowns using advanced lithium silicate or disilicate materials, but new printing technology with very high temperature nozzles to melt the glass ceramic as it moves out of the nozzle will need to be developed.

“We must consider that printing ceramic materials strong enough for permanent restorations requires a lot of heat,” explains Carden. “The machines currently on the market are not equipped to handle those temperatures. Creating technology that can print those materials is something that can definitely happen down the line. There are machines out there that can do these things, but right now they’re in the prototype phase.”

Closer to developmental reality are materials and applications for additive manufacturing that would allow production of long-term temporaries printed in a variety of shades, flexible partials with the biocompatibility and strength to be placed directly in the patient’s mouth, orthodontic aligners thermo-formed over a series of 3D printed models that are computer designed to project corrective tooth realignment over a period of time, or even dentures complete with teeth and characterized with a variety of colors. Any one of these new developments would require developing materials that can withstand the oral environment.

“The biggest challenge at the moment is developing materials that are biocompatible and strong enough to withstand the extreme conditions of the oral environment,” says Cohen. “In terms of mechanical properties, the materials would need to perform the same on day one in the mouth as day 1000.” And if such materials were to be developed, it would open the door for other end products such as anti-snoring and bruxism devices.

Medical Applications

Researchers are not just concerned with 3D printing’s applications in dental technology, but in medicine in general. Amazing medical applications for 3D printing are being discovered every day, with companies 3D printing pills, futuristic casts, and even functioning human organs.

One such researcher is Michael McAlpine, a material scientist and head of the McAlpine Research Group at Princeton University. McAlpine’s group developed and 3D printed a bionic ear. Not only would this manufactured organ allow deaf people to hear, but it could also give people with normal hearing the ability to hear frequencies normally unrecognizable by the human ear.

According to McAlpine, 3D printing was the best method for creating this bionic organ, as it allowed them to “grow” both the ear and the electronics together, at the same time. “We turned to 3D printing because the technology allows you to go layer by layer, which means that the electronics and living tissue can be intertwined. Depending on what kind of materials you put into the print, you can print electronics and biology all together in a completely interwoven form from the bottom up. It’s just a new avenue that we can use to achieve our research goals,” says McAlpine.

McAlpine is not the only researcher 3D printing living tissue. Scientists in a US Bio­tech­nology Com­pany 3D printed a functioning, albeit miniaturized, human liver.2 While this tiny organ only survived for 5 days, it is an integral first step towards being able to produce human organs without the need for a donor.

Long-Distance Dentistry?

Because 3D printing is so open-ended, many companies have also used it for novelty purposes. However, these novelty 3D printing endeavors may have far-reaching effects on the dental industry without even intending to. For example, “Clone Factory” is a Japanese company that, for the price of about $1,300, will scan a person’s face and have their features 3D-printed onto an 11-inch doll.3 While this is a really interesting niche market, the ability to 3D print human faces with photo-realistic accuracy could be extremely useful in the medical field. Imagine if clinicians or technicians were able to 3D print a patient’s entire head, including the inside of their mouth, with 100% accuracy. From there, they could conduct try-ins and modify restorations to achieve functional and esthetic perfection, even if they never get the opportunity to meet the patient in person. Practitioners could treat patients on the other side of the planet just as effectively as they would be able to treat a patient who lives right next door. Although treatment such as this is probably far away, current technology means that it is no longer completely far-fetched.

Conclusion

3D printing is a rapidly emerging technology that has the future potential to change the manufacturing structure of the dental industry. Although the technology is still in its infancy, rapid advances in new materials and 3D-printing equipment are on the not so distant horizon. As with any new technology, the barriers to entry are cost and speed of production. But all that could change and change quickly as the practicalities of the technology better and more fully meet the needs of the end user.

References

1. Manyika J, Chui M, Bughin J, et al. Disruptive technologies: Advances that will transform life, business, and the global economy. Report: McKinsey Global Institute. Updated May 2013. www.mckinsey.com/insights/business_technology/disruptive_technologies. Accessed May 7, 2014.

2. Clark L. Bioengineers 3D print tiny functioning human liver. wired.co.uk website. Updated April 24, 2013. www.wired.co.uk/news/archive/2013-04/24/3d-printed-liver. May 7, 2014.

3. Jauregui A. Human Doll Cloning: Japanese Company 3D Prints Real People’s Faces on Toys. Huffington Post website. Updated May 22, 2013. www.huffingtonpost.com/2013/05/22/human-doll-cloning-japan-3d-printing_n_3320513.html. Accessed May 7, 2014.


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