Mounting evidence of role immune system plays in degrading tooth and restorations: U of T Dentistry study

Bacteria and neutrophils together cause havoc on dental restoration

In the mouth, acids and stimulants from bacteria and cells of the innate immune system, known as neutrophils, destroy the bond adhesives commonly used in resin composite dental restorations. That’s according to a new study out of the University of Toronto’s Faculty of Dentistry published recently in scientific journal Acta Biomaterialia.

The study follows up on previous work in which researchers discovered a uniquely destructive role played by neutrophils in collaboration with bacteria to degrade the tooth and tooth-coloured restorations.

For this study, the team wanted to see whether certain restoration materials were more or less susceptible to this “natural storm” of destruction, and how quickly damage is done.

The team looked at one particular resin composite tooth-coloured restoration, but two types —total-etch and self-etch — of bond adhesive systems used to affix the restoration to the teeth.

Total-etch adhesive requires the addition of an acid to adhere the restoration to the tooth’s surface. Self-etch systems, on the other hand, already contain an acid component, and bond to the tooth directly.

The two systems were applied onto extracted teeth and exposed to neutrophils and bacterial stimulants over the course of 30 days.

Long considered the gold standard in dental restorations, total-etch system adhesive took considerable damage in a short amount of time, says senior author of the study, Faculty of Dentistry professor Yoav Finer. “You can see a huge impact on the bond between the restoration and the tooth in as little as two days,” he says.

Conversely, the self-etch system adhesive was shown to fare much better, but still retained damage caused by the neutrophil-induced environment.

“This research adds another layer of our understanding of the complexity of dental caries,” says the study’s lead author, Russel Gitalis, who earns a Master of Science in Dentistry from U of T in the fall of 2020. “We started to identify what factors from the neutrophils could be responsible for the damage,” Gitalis adds, pointing out that more work needs to be done.

In fact, says Finer, who holds the George Zarb/Nobel Biocare Chair in Prosthodontics, several factors from the neutrophils were found that could contribute to the damage in restorations and teeth. “Now we need to work with the individual factors to understand the underlying mechanisms.”

Both authors underscore that bacteria are still a vital part of the destruction equation. Bacteria stimulate the neutrophil immune cells, explains Finer, adding that “factors from the bacteria contribute to the damage and accelerated the neutrophils.”

The researchers hope that their work on the neutrophil-bacteria connection can yield new understandings and interventions for this globally-pervasive disease. “Better knowledge of caries will allow us to develop [preventive] interventions,” Gitalis says.

Photo: Neutrophils, innate immune cells (in red), are shown here breaking down the interface between a tooth structure (bottom right) and a resin composite restoration (bottom left) (Russel Gitalis)