3D-printed teeth that can kill mouth bacteria
Netherlands-based University of Groningen researchers have announced the development of 3D printed teeth that kill the bacteria Streptococcus mutans, one of the leading causes of tooth decay. The teeth are made with an antimicrobial resin which in testing killed 99% of bacteria, compared to just 1% on normal teeth. The next step is for the team to perform a long term study, to see how the teeth hold up to the stresses of everyday life, for example toothpaste. The material could also be used in tooth repair work, such as crowns, and is ideal for low-resource areas, without regular access to dentistry. 

According to the World Health Organization, poor oral health is tied to "poor living conditions, low education, and lack of traditions.” Some 26 percent of adults have untreated tooth decay. It's particularly prevalent in low income populations, and it's been linked to a whole host of health issues, including heart disease, stroke, diabetes, pneumonia, poor pregnancy outcomes and dementia.

Now, researchers at the University of Groningen in the Netherlands have come up with a way to 3D print teeth and other dental implants out of antimicrobial polymers. The new teeth would kill the bacteria, Streptococcus mutans, which collects in the mouth and causes tooth decay.

3D printing has already started to make its way into dentistry, in the form of replacement teeth and veneers. But chemistry professor Andreas Hermann, who leads the polymer chemistry and bioengineering group at Groningen, and Yijin Ren, head of the university's orthodontic department, agreed that they could go a step further.

“We both rationalized that in times of dentistry going digital it would be beneficial for patients if we can include a bacterial killing property to all 3D printed dental materials,” Hermann says.

Hermann and his team combined antibacterial ammonium salts with standard dental resins. “The antimicrobial resins contain groups that are positively-charged and interact with the outer surface of bacteria,” Hermann says. “We designed the materials in such a way that once bacteria settle on the material the positively-charged groups make holes in the microbes and the bacteria then die.”

Then, they printed the teeth using a Formlabs Form 1 3D printer and a process called stereolithography, which involves depositing the liquid polymer into a mold, layer by layer, and then hardening it with a laser. To make it work, the viscosity of their antimicrobial plastic had to be the same as a conventional one.

The researchers printed teeth with and without antimicrobial properties to test their material. They then put tooth decay-causing bacteria on the samples. More than 99 percent of the bacteria died on the treated teeth, while only about 1 percent were killed on the untreated ones.

Nicholas Staropoli, a research associate for the American Council on Science and Health, said in a review of the study that he thinks the teeth could prevent oral infections, such as endocarditis, and preserve dental implants, which are often broken down by bacteria, but he has some concerns about how the teeth would impact the mouth's microbiome. Could they wipe out bacteria that defend a person from more harmful pathogens?

The dental implants could have huge impacts, especially for people in low-resource areas who don’t have regular access to doctors and dentists. Hermann says that additional costs would be minimal, because the materials his team is using to make the antimicrobial polymer are inexpensive and readily available.

Now, Hermann says they're working on long-term tests to see how the polymer holds up over time and how it interacts with things like toothpaste—to make sure it doesn't breakdown or become less effective with wear, and to see how it impacts the user. He says that the material has immediate application in retainers and that soon it could be used in oral restoration, crowns and replacement teeth.

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