Human Neutrophils Degrade the Restoration-tooth Interface

Objectives: Methacrylate-based polymeric resin composites are currently the most popular restorative biomaterials used in dentistry with >160 million procedures/annum in North America. However, due to their limited long-term stability, 70% of the placed restorations are replacement for failed restorations at a huge economic burden of $30B/y. The restoration-tooth interface is susceptible to oral enzymes. In addition to salivary and bacterial esterases, the formation of biofilm on the tooth surface creates a microbial challenge and induces a host response, leading to the recruitment of neutrophils in the oral cavity.
Hypothesis: Human neutrophils (HN) possess protease activity and could degrade the restoration-tooth interface, as measured by the fracture toughness of the bond between the restoration and the tooth. Therefore, the main objective was measuring HN protease, Metalloproteinase-like activities (MMP) and HN ability to reduce the interfacial bond strength of resin composite bonded to human tooth dentin using a total-etch adhesive system.
Methods: Freshly isolated HN were tested for MMP-like activity using generic MMP substrate. Miniature Short-Rod (Mini-SR) tooth-restoration specimens made from resin composite (Z250, 3M) bonded to tooth dentin using a total-etch adhesive (ScotchBond MP, 3M) were incubated in Hank’s buffered salt solution (HBSS) with or without freshly isolated HN, stimulated with lipopolysaccharides, for up to 30-days. Specimens were then loaded in tension until fracture using a Universal Testing Machine.
Results: Stimulated HN possess generic MMP-like activity (70µmol/min/millionHN). Mini-SR specimens incubated with HN showed a reduction in their interfacial bond strength compared with specimens incubated in HBSS alone after 2-days (KIC=0.84MPa√m versus KIC=1.15MPa√m) and 30-days (KIC=0.59MPa√m versus KIC=0.95MPa√m)(Fig.1)(p<0.05).
Conclusions: Stimulated HN showed collagenase activity and caused a reduction of the fracture toughness of total-etch bonded interface, which could lead to premature restoration failure. Elucidating host-biomaterial interactions would allow for the development of more resistant biomaterials to reduce interfacial degradation and health burden faced by the patients.