Antibacterial activity and shear bond strength of fiber‑reinforced composites and bonding agents containing 0.5%, 1%, 2.5%, and 5% silver nanoparticles

Abstract

Background: Bonded composites may increase bacterial accumulation and caries formation risk.
Therefore, assessment of methods to decrease bacterial activity around them would be valuable.
The literature on the efficacy of adding silver nanoparticles to fiber‑reinforced composite (FRC)
or adding them to bonding agents in terms of their antibacterial activity and/or shear bond
strength (SBS) is scarce. Thus, we aimed to assess the antibacterial activity of flowable composites
and bonding agents containing various percentages of experimental silver nanoparticles (nanosilver)
against S. mutans and to evaluate the SBS of FRC and bonding agents containing different amounts
of nanosilver to enamel.
Materials and Methods: In this preliminary study, 0% (control), 0.5%, 1%, 2.5%, and 5%
nanosilver were added to flowable composite and bonding agent. Syntheses of nanosilver and
nanosilver‑incorporated composite specimens were approved using X‑ray diffraction spectroscopy
and scanning electron microscopy. Antibacterial effects of the produced materials on S. mutans were
evaluated by colony count with serial dilution method (n = 7 groups × 10 [n = 70] specimens) and
agar disc diffusion test (n = 6 groups × 5 [n = 30] composite specimens + n = 6 groups × 5 [n = 30]
light‑cured bonding + n = 6 groups × 5 [n = 30] uncured bonding) against negative control and
cefotaxime antibiotic. Moreover, SBS values of various FRC blocks bonded to enamel using various
bonding agents were measured (n = 9 groups × 6 [n = 54] human premolars). Data were analyzed
using Kruskal–Wallis, Dunn, two‑way analysis of variance, and Tukey’s tests (α = 0.05).
Results: Composite discs containing all concentrations of nanosilver reduced S. mutans colony
counts (P < 0.05); bacterial growth was ceased at samples containing 2.5% and 5% of nanosilver.
The reduction in the SBS of FRCs was significant only for 5% nanosilver (P < 0.05).
Conclusion: Adding 0.5%, 1%, and 2.5% nanosilver to composite and 0.5% or 1% nanosilver to
bonding agent led to a significant antibacterial behavior against S. mutans while not significantly
affecting the SBS of FRC.
Key Words: Antibacterial efficacy, bonding agents, dental materials, fiber‑reinforced composite,
flowable composite, nanoparticles, orthodontics, Streptococcus mutans