Hydrolytic Activities from Human Neutrophils toward Dental Monomers and Tooth Dentin

Zhou, Liangyi 1, 2 ;  Zaman, Shawket 1, 2 ;  Li, Zhongjie 1, 2 ;  Glogauer, Michael 1, 3 ;  Finer, Yoav 1, 2

1. Dental Research Institute, Faculty of Dentistry, University of Toronto; 2. Institute of Biomaterials and Biomedical Engineering, University of Toronto; 3. Matrix Dynamics Group, Faculty of Dentistry, University of Toronto

Background: Methacrylate-based polymeric resin composite are the most popular dental restorative material. However, the ester groups of their polymer networks are susceptible to hydrolysis by salivary and bacterial esterases. Tooth dentin contain matrix metalloproteinases (MMPs) that degrade dentinal collagen. These degradative activities adversely affect these materials and the material-tooth interface, accelerating the premature failure of the restoration. In the oral cavity, dental restorations are continuously exposed to neutrophils, hypothesized to have and contain esterases and collagenases activities that could enhance degradation of the materials and the restoration-tooth interface.

Hypothesis: Human blood neutrophils release cholesterol esterase-like (CE-like) and MMP-like activities that are detrimental to dental restorative materials.

Objective: To measure CE-like and MMP-like activities of human blood neutrophils and determine their degradative activities on methacrylate-based, bisphenol-glycidyl-dimethacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) monomers.
Materials & Methods: Freshly isolated human blood neutrophils (UofT Ethics Protocol #29410) were tested for CE-like and MMP-like activities using previously established assays. The effects of the CE-like degradative activity were determined by quantification of TEGDMA rate of elimination and production of BisGMA derived biodegradation by-product, bishydroxy-propoxy-phenyl-propane (BisHPPP) using high performance liquid chromatography.

Results: The CE-like activity of human blood neutrophils (1x106 cells/mL) toward para-nitrophenylbutyrate (p-NPB) were demonstrated to be higher than human saliva (16 units/mL). While the levels of TEGDMA did not change, there was an increase in the amount of BisGMA degradation and BisHPPP release (0.79 µg•hr/mL) throughout the 37°C incubation period in the presence of cells vs. media only conditions. Blood neutrophils (25k cells/mL) exhibited a significantly higher MMP-like activity (0.736 µM/min) compared to MMP-8 standard (0.564 µM/min) (p<0.05) and media controls (0 µM/min) (p<0.001).

Conclusions: This study demonstrated that human blood neutrophils contain MMP-like activities and CE-like activities at levels that can degrade BisGMA and dentinal collagen. The effect was material dependant.

Significance/Impact: Biodegradation of methacrylate-based polymeric restorations and dentinal collagen by blood neutrophils enzymatic activities could compromise the resin-dentin interface and reduce the longevity of dental restorations.

Acknowledgements: CIHR MOP 115113; NIH R01DE021385-0