Antimicrobial potential of strontium against bacteria associated with peri-implantitis

Dental implants are nowadays a standard treatment to replace missing teeth and restore function and aesthetics. However, biological complications associated with implants, e.g., peri-implant infections, are common and jeopardize the success of treatment. The main aim of this thesis was to explore strontium (Sr) as a possible prevention strategy against peri-implant infections, since Sr has been shown to have antibacterial action and also to promote titanium (Ti) implant osseointegration. In this thesis, a systematic appraisal of the literature about the antimicrobial potential of Sr-functionalized Ti surfaces for oral applications was performed, and was followed by a series of in vitro studies assessing the antimicrobial potential of Sr against micro-organisms associated with peri-implantitis. In Study I, the systematic appraisal of the literature resulted in an initial list of 1081 potentially relevant publications, where from nine publications from in vitro studies met the inclusion criteria. Most of the included studies showed that Sr-functionalized Ti exerted a limited immediate (i.e., 24 h) antimicrobial effect, likely due to a low Sr ion release; a relevant antimicrobial effect and biofilm inhibition potential against Streptococcus aureus was observed at both early and late timepoints, with an adequate Sr ion release. Study II assessed, in vitro, five different concentrations of soluble Sr(OH)2 (100, 10, 1, 0.1, and 0.01 mM) against 6 different mono-species bacteria (Streptococcusmitis, Staphylococcus epidermidis, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Escherichia coli, and Fusobacterium nucleatum) in terms of cell growth, minimal inhibitory concentration (MIC), and biofilm viability. In the agar diffusion test, zones of inhibition were only observed for 0.01, 0.1, and 1 mM of Sr(OH)2 against P. gingivalis. Growth inhibition in planktonic cultures was achieved at 10 mM for all species tested. In the biofilm viability assay, 10 and 100
Paper III and IV in dissertation as manuscript