Study Examines Bacteria’s Effect on Composite Restorations

A major reason for dental resin composite restoration replacement is secondary caries promoted by acid-producing bacteria, including Streptococcus mutans. A recent study¹ by researchers at the University of Toronto shows that this major cariogenic bacteria also produces enzymes that hydrolyze resin components of adhesives and composites, providing a possible contributing explanation for the increased rate of secondary caries around resin composite restorations.

The study examined the ability of S. mutans to degrade resin composites and adhesives through the bacteria’s esterase activities. Researchers assessed the degradation of resin composite, total-etch and self-etch adhesives after incubation with S. mutans by measuring a Bis-GMA-derived by-product, BisHPPP. BisGMA is a universal component of dental resin composites and adhesives.

The results suggest that S. mutans can degrade resin composites and adhesives through the bacteria’s esterase activities. Esterase-mediated degradation occurred in all materials used in the study, to varying degrees. A critical factor in determining a restoration’s biochemical stability appeared to be the material’s chemistry.

Dr. Yoav Finer, the study’s lead researcher and a member of CDA’s Committee on Clinical and Scientific Affairs, explains how the findings might account for the higher incidence of failed resin composite restorations compared to amalgam: “When present within the confined space of the restoration–tooth marginal interface, S. mutans produces both acids and esterases, affecting the hybrid layer, tooth and composite, ultimately compromising the integrity of the margins and potentially reducing the longevity of the restoration.”

According to Dr. Finer, the study adds to the group’s previous work with S. mutans that showed biodegradation of resin composites increases bacterial virulence: “Our previous studies have shown that resin composite degradation by-products released by salivary and bacterial esterase increase the ability of S. mutans to produce acids, survive in an acidic environment and form dental plaque,” says Dr. Finer.

The authors say that this study points to the need for manufacturers to assess dental resin composites and adhesives for biostability—not only their mechanical properties.