Abstract
Dental caries and periodontal disease are the most prevalent diseases affecting the oral cavity. The diseases are caused by the accumulation and maturation of bacteria on the tooth surface, or gingival tissue, respectively. Thus, the prevention of dental caries and periodontal disease is targeted at the control of dental plaque and current management techniques have limited success. Toward the goal of creating a new and effective treatment strategy for the management of periodontal disease and peri-implantitis we have synthesised an antimicrobial silver nanoparticle- (AgNP) containing hydrogel which is both biocompatible and mucoadhesive. We highlight the novel synthetic approach and have demonstrated the strong antibacterial effects of the hydrogel in vitro on planktonic and biofilm bacterial cells and the promising effects in vivo. We anticipate the gel will be administered into sp aces around the site of infection and will have superior retention and substantivity to current treatments.
For AgNP synthesis and surface enhancement, the microemulsion (µEm) method was used. AgNP characterisation utilised dynamic light scattering (DLS) and transmission electron microscopy (TEM). The synthesised thioctic acid capped-AgNPs were 2-7 nm in diameter, spherical and monodisperse. The produced AgNP suspensions were aqueously dispersed, highly concentrated (≤ 3025 µg mL-1) and demonstrated particle stability at pH 9. Upon incorporation of the AgNPs into the hydrogel, the deprotonated, terminal carboxylate groups of the thioctic acid capped-AgNPs appeared to form cross-linking bridges with the divalent cations and alginate polymer, chemically binding the AgNPs within the hydrogel matrix. The structural and rheological properties of AgNP-containing hydrogels were analysed by cryo-TEM, micro-CT imaging and rheology studies. When AgNPs were cross-linked within the hydrogel structure there was an increased mechanical strength of the gel. To establish the antimicrobial prop erties of the AgNP-containing hydrogel, we optimised a Live/dead fluorometric viability assay using a range of standard and oral associative microorganisms; Escherichia coli, Staphlocuccus aureus, Ps.aeruginosa, Streptococcus mutans, Strep.mitis, Enterococcus faecalis, Strep.gordonii and Candida albicans. A minimal bactericidal silver mass and minimal fungicidal silver mass were determined to be 9.8 µg and 2.4 µg of Ag, respectively. The AgNP-containing hydrogel was tested on pre-formed monoculture biofilms via the membrane sandwich technique, and caused high scale cell death, reduced biomass, and resulted in silver penetration of the biofilms.
A year-long in vivo animal trial was performed by a collaborator to test the efficacy, retentive features and safety of the mucoadhesive AgNP-gel on artificially-induced periodontal disease and peri-implantitis infection sites. A single application of the gel (containing ~39 µg Ag) was retained in the periodontal pockets for up to 4 months and showed signs of reduced inflammation and signs of attempted new bone growth in both periodontal disease and peri-implantitis compared to untreated control infection sites.
The second part of this thesis focused on AgNP modification of glass ionomer cement dental restoratives with the intent to reduce the occurrence of secondary caries. A 6.4 µg-AgNP-modified commercially-available GIC had an increased flexural strength value, an equivalent cement colour, and an improved anti-adherent biofilm surface compared to the commercially-available GIC. Furthermore, work was conducted towards the production of an ‘in-house’ hybrid GIC, in which the AgNP-containing hydrogel technology was combined with that of the GIC.