Volume 7 • 2020 • Issue 1

N ews and E vents New Research: White Blood Cells Linked to Tooth Decay Previous research has shown that tooth decay is caused only by bacteria, but a new study 1 offers evidence that the immune system—specifically white blood cells called neutrophils—could also play a part in decay. “It is hard to believe that our immune system would play a part in creating cavities,” says Dr. Yoav Finer, the lead author of the study at the University of Toronto’s Faculty of Dentistry. “Now we have evidence.” Fifty-five to 70% of white blood cells are neutrophils, which lead the body’s immune response. When bacteria invade the oral cavity, the body sends neutrophils, which enter the oral cavity from the gums around the roots of the teeth, to attack. Acid from bacteria demineralize the teeth, and eventually could form cavities. When battling these bacteria, enzymes from neutrophils could cause damage to the demineralized tooth and also to composite fillings. “It’s like when you take a sledgehammer to hit a fly on the wall,” Dr. Finer says. “That’s what happens when neutrophils fight invaders.” The Experiment The researchers incubated parts of demineralized dentin from extracted teeth, uncured resin and cured resin composite with neutrophils isolated from human blood. After 24 to 48 hours, the researchers measured the level of uncured resin and tooth degradation. The degradation of the cured composite resin was measured at intervals of 48 and 96 hours. Results Uncured resin degraded within 24 hours, and demineralized dentin and cured composite resin sustained damage within 1 to 2 days. “We can actually see them breaking down using electron microscopy,” says the study co-author, Dr. Michael Glogauer. “This suggests that neutrophils could contribute to primary tooth decay and recurrent caries,” says Mr. Russel Gitalis, a MSc candidate in Drs. Finer and Glogauer’s group and a co-author of the study. Gitalis says that the experiment is the first to show that neutrophils can break down resin composites, which may explain the higher rate of caries recurrence in patients whose caries are treated with composites. What’s Next ? The researchers see potential for more research into the interaction of the immune system and bacteria, and its consequence for oral health. “We can develop new methods to prevent immune-mediated destruction of teeth,” says Dr. Glogauer. Dr. Finer says that new standards for testing filling materials may need to take neutrophils into account. The study revealed “potential weakness in current restorative procedures and materials used to manage gingival proximal and cervical gingival or sub-gingival carious lesions.” Neutrophils enter the oral cavity via the gingival sulcus, so their effects are concentrated on teeth or cured composite resin nearby. The group will continue research in this area with the support of the Canadian Institutes of Health Research. a Issue 1 | 2020 | 27 Reference 1. Gitalis R, Zhoua L, Marashdeh MQ, Sun C, Glogauer M, FinerY. Human neutrophils degrade methacrylate resin composites and tooth dentin. Acta Biomater. 2019 Apr 1;88:325–31.