Dental Tribune International

Human immune system contributes to dental caries and damage to dental fillings

By Dental Tribune International
April 23, 2019

TORONTO, Canada: The question as to why the human immune system partly works against the body, for example in autoimmune diseases, is still not sufficiently researched. Usually, it is the conjunctive tissue that is affected. However, a recent study by researchers from the University of Toronto has shown the first evidence that the body’s own defense system could be a major contributor to dental caries and filling failure.

“No one would believe that our immune system would play a part in creating cavities,” said lead author Dr. Yoav Finer, an associate professor in the Faculty of Dentistry at the university. “Now we have evidence.”

The study demonstrated that the decay of dentin and fillings is caused not only by bacteria—as has been the common understanding of scientists for decades—but through the unique activity of oral immune cells known as neutrophils, which potentially enhance the effects of bacteria.

Recognized as important in combating inflammation in all parts of the body, the neutrophil is a type of short-lived innate immune system cell that enters the oral cavity from the gingivae around the roots of the teeth. When bacteria invade the oral cavity, the body sends out neutrophils to attack. However, as the neutrophils track down and destroy the invading bacteria, they may cause destruction to the localized environment as well.

On their own, neutrophils are incapable of causing damage to the teeth. Finer explained: “They don’t have acid, so they can’t do much to mineralized tooth structures.” However, if neutrophils engage in attack, the acids produced by oral bacteria demineralize the tooth. That is when enzymes from both the immune cells and their targets, the bacteria, rapidly degrade teeth and can cause collateral damage to resin composite fillings.

Corroborating the findings of previous studies conducted by the group, the research also explained why so many patients who have composite fillings as a result of caries treatment face high rates of recurrence of the disease. Most composite fillings fail within five to seven years, costing Canadians an estimated CA$3 billion a year.

“Ours is the first basic study to show that neutrophils can break down resin composites and demineralize tooth dentin,” said Russel Gitalis, a master’s student at the university and first author of the paper. “This suggests that neutrophils could contribute to tooth decay and recurrent caries.”

While the study provides the first direct evidence that an immune response may contribute to dental caries, it also opens up new possibilities for research. “We can develop new methods to prevent immune-mediated destruction of teeth,” said co-author Prof. Michael Glogauer, from the Faculty of Dentistry at the university.

The findings may also one day lead to new standards for testing filling materials, said Finer, who argues that materials need to face trial within the collaborative destruction laboratory to pass muster. “We need to test interactions with the body and bacteria,” he added.

The study, titled “Human neutrophils degrade methacrylate resin composites and tooth dentin”, was published on April 1, 2019, in Volume 88 of Acta Biomaterialia.

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