For tens of millions of people, dental implants have provided a way to replace missing teeth with fixed, functional replacements rather than removable dentures. However, an estimated 10% to 20% of implant patients eventually develop peri-implantitis, a serious infection that damages the surrounding jawbone. Antibiotics frequently fail to control this condition, and scientists have struggled to understand why.
A new study by researchers at the Rutgers School of Dental Medicine suggests the answer lies not just in the bacteria, but in the implant material itself. The team found that bacteria accumulating on implant surfaces create acidic biofilms that slowly corrode titanium, releasing billions of microscopic metal particles, each smaller than a red blood cell. These particles can also be dislodged during routine dental cleaning when metal instruments are used.
Once released into the gums, the titanium fragments attract a bacterial toxin known as lipopolysaccharide, which coats their surfaces. This combination makes the particles resemble unusually large bacteria that cannot be broken down. Macrophages, the immune cells that engulf and destroy harmful microorganisms, attempt to consume the particles but become trapped in a prolonged state of excessive inflammation.
The researchers traced the destructive process to TRPC1, a calcium channel in macrophages. When this channel was disabled in genetically engineered mice, the animals developed dramatically smaller abscesses, produced fewer inflammatory signaling molecules, and regained the ability to clear bacteria.
"For the first time, we show why all the antibiotic treatments that work around teeth do not work around implants," said Georgios Kotsakis, senior author of the study and assistant dean for clinical research at Rutgers School of Dental Medicine. "Now that we know the cause, we can start developing therapeutics."
Laboratory experiments revealed that macrophages exposed to titanium particles engulfed fewer than half as many bacteria as immune cells that had not encountered the particles. "These particles are little magnets that attract the bacterial toxin, and they hijack the immune system, preventing it from clearing bacteria," said Kotsakis. "You have a perfect storm that defies antibiotics."
The study also reinforces the importance of proper cleaning. Nonabrasive cleaning methods have become standard practice after research showed that metal scalers used on natural teeth can damage and corrode titanium surfaces, potentially accelerating the disease.
With funding from the National Institutes of Health, Kotsakis and his colleagues are now evaluating potential drugs that act on the same molecular pathway in human cells.