Novel Bifunctional Nanofiller (Bioactive\Antimicrobial) for Improving Dental Adhesives Efficacy

Purpose: The objective of this study was to develop novel bio-composite Nanofiller (Quaternary polyethyleneimine\ Hydroxyapatite, QPEI/HAp), which combines the antibacterial activity of polymeric quaternary ammonium salt and the multi-advantages of Hydroxyapatite nanoparticles for improving biological and physico-mechanical properties of Dental Adhesives. Materials and Methods: Hydroxyapatite (HAp) nano rods were produced by hydrothermal process and coated by Polyethyleneimine (PEI) via electrostatic adsorption, followed by two steps polymeric reaction; tertiary amination and quaternization. The resulting powder was characterized using XRD, FTIR and TEM before and after polymer coating, and bioactivity was evaluated after 7 days soaking in simulated body fluid using XRD analysis. An experimental ethanolbased one-bottle adhesive resin was formulated with 0.2, 0.5, 1, 2 and 5% QPEI/HAp nanofiller. The formulated adhesive resins were evaluated for their colloidal stability, antibacterial activity, Ultimate Tensile Strength, and Micro-Shear bond strength to dentin. Results: Powder characterization confirmed successful surface modification of Hydroxyapatite nanoparticles with PEI polymer; the particles presented a high crystallinity with typical chemical groups and mean size around 20 nanometers. XRD analysis revealed nucleation of apatite crystals on the surface of QPEI/HAp nanoparticles after soaking in SBF; confirming their bioactivity. Lower contents of modified nanoparticles showed little or no aggregation tendency and good colloidal stability in the adhesive solution with Zeta potential of 30.6 mV. Antibacterial outcomes of PEI against S. mutans was significantly higher than that of MDPB in Clearfil Protect bond; a commercial adhesive used as control (P<0.05). The addition of 0.2 wt. % modified nano-hydroxyapatite resulted in higher values of Ultimate Tensile and Micro-Shear bond strength than other tested adhesives and commercial Clearfil S3 Bond (all-in-one adhesive); (P<0.05). Conclusion: Incorporation of 0.2 wt. % QPEI-HAp nanoparticles significantly improved the adhesive properties and may be promising multifunctional filler for dental adhesive resin.