Influence of carbon and graphene oxide nanoparticle on the adhesive properties of dentin bonding polymer: A SEM, EDX, FTIR study.

Objective: This study was aimed at including 2.5 wt.% of carbon nanoparticles (CNPs) and graphene oxide NPs (GNPs) in a control adhesive (CA) and then investigate the effect of this inclusion on their mechanical properties and its adhesion to root dentin.

Materials and methods: Scanning electron microscopy and energy dispersive X-ray (SEM-EDX) mapping were conducted to investigate the structural features and elemental distribution of CNPs and GNPs, respectively. These NPs were further characterized by Raman spectroscopy. The adhesives were characterized by evaluating their push-out bond strength (PBS), rheological properties, degree of conversion (DC) investigation, and failure type analysis.

Results: The SEM micrographs revealed that the CNPs were irregular and hexagonal, whereas the GNPs were flake-shaped. EDX analysis showed that carbon (C), oxygen (O), and zirconia (Zr) were found in the CNPs, while the GNPs were composed of C and O. The Raman spectra for CNPs and GNPs revealed their characteristic bands (CNPs-D band: 1334 cm^-1, GNPs-D band: 1341 cm^-1, CNPs-G band: 1650 cm^-1, and GNPs-G band: 1607 cm^-1). The testing verified that the highest bond strength to root dentin were detected for GNP-reinforced adhesive (33.20 ± 3.55 MPa), trailed closely by CNP-reinforced adhesive (30.48 ± 3.10 MPa), while, the CA displayed lowest values (25.11 ± 3.60 MPa). The inter-group comparisons of the NP-reinforced adhesives with the CA revealed statistically significant results (p < 0.01). Failures of adhesive nature were most common in within the adhesives and root dentin. The rheological assessment results demonstrated a reduced viscosity for all the adhesives observed at advanced angular frequencies. All the adhesives verified suitable dentin interaction shown by hybrid layer and appropriate resin tag development. A reduced DC was perceived for both NP-reinforced adhesives, compared to the CA.

Conclusion: The present study's findings have demonstrated that 2.5% GNP adhesive revealed the highest, suitable root dentin interaction, and acceptable rheological properties. Nevertheless, a reduced DC was observed (matched with the CA). Prospective studies probing the influence of diverse concentrations of filler NPs on the adhesive's mechanical properties to root dentin are recommended.