Dental Implants May Be Fueling Their Own Infections as Titanium Particles Hijack Immune Cells, Study Finds

NEWARK, N.J. — Infections around dental implants are notoriously hard to cure. New research suggests part of the reason may be the implants themselves.

Scientists at the Rutgers School of Dental Medicine report that bacteria can slowly corrode titanium implants and shed microscopic metal particles into the surrounding gum tissue. Those particles disrupt the immune cells meant to fight infection. Instead of clearing bacteria, the cells get stuck in a state of runaway inflammation that eats away at the jawbone holding the implant in place.

The findings, published in the journal PNAS Nexus, offer an explanation for why antibiotics often fail against the condition, known as peri-implantitis. They also point to a possible new drug target.

"For the first time, we show why all the antibiotic treatments that work around teeth do not work around implants," said Georgios Kotsakis, the study's senior author and assistant dean for clinical research at Rutgers School of Dental Medicine. "Now that we know the cause, we can start developing therapeutics."

A common and costly problem

Dental implants, titanium posts anchored in the jawbone to support artificial teeth, have become a widely used alternative to dentures for tens of millions of people. But an estimated 10% to 20% of implant patients eventually develop peri-implantitis, a serious infection that destroys the bone around the implant.

Rutgers estimates the condition costs health systems worldwide more than $1 billion a year.

Peri-implantitis closely resembles periodontitis, the gum disease that affects natural teeth. Both are triggered by the same kinds of oral bacteria. But they respond very differently to treatment.

Around natural teeth, antibiotics combined with professional cleaning usually resolve the infection. Around implants, the same approach works in fewer than half of cases, according to the researchers, and bone loss can continue even with treatment.

For about two decades, research focused mainly on the bacteria behind these infections. Kotsakis' team looked instead at whether the implant material plays a role.

How the particles cause harm

The researchers found that bacteria building up on implant surfaces form acidic films that gradually corrode the titanium. Over time, that corrosion can release billions of tiny metal particles, each smaller than a red blood cell.

Once in the gum tissue, the particles become coated with lipopolysaccharide, a toxin produced by bacteria. To the immune system, the coated particles look like unusually large bacteria.

Macrophages, the white blood cells that swallow and destroy invading microbes, try to engulf them. But they cannot break down titanium. The cells then become locked in a prolonged inflammatory state, pumping out signaling molecules such as interleukin-1 beta. That protein has also been linked to inflammation in rheumatoid arthritis and Alzheimer's disease.

The inflammation breaks down the bone supporting the implant. At the same time, the immune cells become worse at their main job. In laboratory tests, macrophages exposed to titanium particles engulfed fewer than half as many bacteria as cells that had not been exposed.

"These particles are little magnets that attract the bacterial toxin, and they hijack the immune system, preventing it from clearing bacteria," Kotsakis said. "You have a perfect storm that defies antibiotics."

A potential drug target

The team examined human tissue samples, tested human immune cells in the lab and ran experiments in genetically engineered mice. They traced the damaging reaction to TRPC1, a calcium channel in the membrane of macrophages that is activated by the titanium particles.

Mice bred without TRPC1 responded far better when exposed to the same mix of titanium particles and bacteria. They developed much smaller abscesses, produced fewer inflammatory molecules and regained the ability to clear bacteria. Disabling the channel prevented the destructive disease seen in normal mice.

Rutgers describes the discovery as the first credible drug target for peri-implantitis. It suggests a treatment that calms the immune system's misfiring response, rather than relying only on antibiotics, could protect bone around implants.

With funding from the National Institutes of Health, Kotsakis and his colleagues are now testing drugs that act on the same pathway in human cells.

The work is still at an early stage. Results in mice and lab-grown cells do not always carry over to people, and any new treatment would need years of clinical testing before reaching patients.

What implant patients can do now

The researchers say the findings also reinforce how implants should be cleaned.

Titanium particles can come loose not only through bacterial corrosion but also during dental cleanings. This is especially likely when metal instruments designed for natural teeth are used on implants, because they can scratch the surface.

Until about a decade ago, many dentists used the same metal scalers on implants as on natural teeth. Research by the Rutgers team and others has since shown that these tools can damage and corrode titanium, potentially releasing more particles and speeding up disease.

Gentler, nonabrasive cleaning methods are now standard practice. Regular professional cleaning remains the best known protection against peri-implantitis.

For patients, that means keeping up with dental visits and making sure implants are cleaned with techniques suited to them.

The study was led by Juliana Girón Bastidas, with co-authors Danyal A. Siddiqui, Viviane Nascimento Da Conceicao, Yuyang Sun, Mashael Al Thunayan, Brij B. Singh and Kotsakis.