Pathways of neutrophil enzymatic degradation of resin-based composites and adhesives

Human neutrophils (HN), white blood cells of the innate immune system, are abundant inhabitants of the oral cavity. It was previously found that these leukocytes can degrade methacrylate resin-based composites (RC), adhesives, monomers, and demineralized dentin. This activity can compromise the tooth-restoration interface, potentially resulting in restoration failure and debonding. Nevertheless, the exact mechanism of this activity is yet to be fully determined. The objectives of this study were to measure cluster of differentiation (CD) marker expression and cell viability of HN when exposed to methacrylate resin-based monomers, degradative byproducts, RC, and adhesives, and to measure and analyze neutrophil-derived enzymes' degradative activity towards methacrylate resin-based materials. HN's CD marker expression in the presence of methacrylate resin-based monomers, degradative byproducts, composites, and adhesives was quantified via flow cytometry analysis using a panel of 7 CD markers. HN and neutrophil-derived enzyme degradation of methacrylate resin-based materials was analyzed using ultra performance liquid chromatography and mass spectrometry. Lastly, in silico 3D characterization of the neutrophil-derived enzymes catalytic site was conducted. Results showed increased CD66a among HN exposed to RC and universal-etch adhesive (UE), and upregulated CD11b and CD18 following exposure to UE. Whole HN and neutrophil elastase (NE) degraded 2,2-Bis [4-(2-hydroxy-3-methacryloxypropoxy) phenyl] propane (bisGMA) and urethane dimethacrylate (UDMA) monomers, and photocured RC and UE dental materials (p < 0.05). In silico 3D characterization of NE's active site revealed selective binding configurations to bisGMA and UDMA monomers. These findings suggest that neutrophil-mediated enzymatic degradation of methacrylate resin-based materials may be an important contributing factor to restoration failure and recurrent caries. STATEMENT OF SIGNIFICANCE: Neutrophils, cells of the innate immune system, are found in the gingival sulcus adjacent to the margins of methacrylate resin-based composites and adhesives. There, neutrophils can combat pathogenic oral bacteria as the body's first line of defense. This study elucidates the mechanism of neutrophil-derived enzymatic degradation of methacrylate dental materials, and identifies neutrophil elastase as a key contributor to this potentially harmful activity. This process, that can occur at the tooth-restoration interfacial margins, may contribute to the premature failure of dental restorations, a multi-billion-dollar health concern. The mechanisms identified in this study can be targeted in preventive dental treatments and should be considered when developing new dental materials.