Background: Peri-implantitis due to infection of dental implants is a common complication that may cause significant patient morbidity. In this study, we investigated the antimicrobial potential of Sr(OH)2 against different bacteria associated with peri-implantitis. Methods: The antimicrobial potential of five concentrations of Sr(OH)2 (100, 10, 1, 0.1, and 0.01 mM) was assessed with agar diffusion test, minimal inhibitory concentration (MIC), and biofilm viability assays against six bacteria commonly associated with biomaterial infections: Streptococcus mitis, Staphylococcus epidermidis, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Escherichia coli, and Fusobacterium nucleatum. Results: Zones of inhibition were only observed for, 0.01, 0.1, and 1 mM of Sr(OH)2 tested against P. gingivalis, in the agar diffusion test. Growth inhibition in planktonic cultures was achieved at 10 mM for all species tested (p < 0.001). In biofilm viability assay, 10 and 100 mM Sr(OH)2 showed potent bactericidal affect against S. mitis, S. epidermidis, A. actinomycetemcomitans, E. coli, and P. gingivalis. Conclusions: The findings of this study indicate that Sr(OH)2 has antimicrobial properties against bacteria associated with peri-implantitis.

The aim of this systematic review was to assess the current scientific evidence of the antimicrobial potential of strontium (Sr) when used to functionalize titanium (Ti) for oral applications. Out of an initial list of 1081 potentially relevant publications identified in three electronic databases (MEDLINE via PubMed, Scopus, and Cochrane) up to 1 February 2021, nine publications based on in vitro studies met the inclusion criteria. The antimicrobial potential of Sr was investigated on different types of functionalized Ti substrates, employing different application methods. Nine studies reported on the early, i.e., 6–24 h, and two studies on the late, i.e., 7–28 days, antimicrobial effect of Sr, primarily against Staphylococcus aureus (S. aureus) and/or Escherichia coli (E. coli). Sr-modified samples demonstrated relevant early antimicrobial potential against S. aureus in three studies; only one of which presented statistical significance values, while the other two presented only the percentage of antimicrobial rate and biofilm inhibition. A relevant late biofilm inhibition potential against S. aureus of 40% and 10%—after 7 and 14 days, respectively—was reported in one study. Combining Sr with other metal ions, i.e., silver (Ag), zinc (Zn), and fluorine (F), demonstrated a significant antimicrobial effect and biofilm inhibition against both S. aureus and E. coli. Sr ion release within the first 24 h was generally low, i.e., below 50 µg/L and 0.6 ppm; however, sustained Sr ion release for up to 30 days, while maintaining up to 90% of its original content, was also demonstrated. Thus, in most studies included herein, Sr-functionalized Ti showed a limited immediate (i.e., 24 h) antimicrobial effect, likely due to a low Sr ion release; however, with an adequate Sr ion release, a relevant antimicrobial effect, as well as a biofilm inhibition potential against S. aureus—but not E. coli—was observed at both early and late timepoints. Future studies should assess the antimicrobial potential of Ti functionalized with Sr against multispecies biofilms associated with peri-implantitis.

Objective To assess whether bacterial colonisation in a power-driven water flosser can be prevented. Materials and methods Twenty-four patients undergoing supportive periodontal treatment used 2 power-driven water flossers [Sonicare AirFloss (SAF), AirFloss Ultra (SAFU)] for 12 weeks each as follows: (a) with bottled water (BW); (b) with BW and cleaning the device extra-orally twice per week with chlorhexidine gluconate or (c) essential-oil-based (EO) mouth-rinse; (d) with EO only. Water-jet samples were taken after 6 and 12 weeks with the used nozzle and after exchanging to a brand-new nozzle. After 12 weeks, all devices underwent an intensive cleaning procedure. Samples were analysed by PCR-based method for cariogenic and periodontal pathogens and culture for staphylococci, aerobe gram-negative bacteria, and Candida sp. Results Contamination of SAF/SAFU with Streptococcus mutans was found in > 95% of the samples; periodontal pathogens and aerobe gram-negative bacteria were detected in 19–56% of the samples, while Staphylococcus aureus and Candida sp. were identified only in few samples. Contamination rate was basically unaffected by time-point, device, or way of use. Further, exchanging the nozzle did not prevent transmission of a contaminated water-jet, but the intensive cleaning reduced most of the pathogens significantly, except of S. mutans. Conclusion Neither a specific way of use nor exchanging the nozzle prevented bacterial colonisation and transmission of biofilm components via the water-jet of SAF/SAFU. Clinical relevance Bacterial colonisation in a power-driven water flosser seems impossible to prevent; to restrict the risk of cross-contamination within a household, one device per person should be recommended.

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 mM Sr(OH)2 showed potent bactericidal effect against S. mitis, S. epidermidis, A. actinomycetemcomitans, E. coli, and P. gingivalis. It was thus concluded that Sr(OH)2 has antimicrobial properties against bacteria associated with peri-implantitis. Study III assessed the in vitro early- and late bacteriostatic and bactericidal effect of Sr-functionalized wafers on bacteria associated with peri-implantitis (E. coli,S. aureus, Streptococcus oralis, Actinomyces naeslundii, Parvimonas micra, P.gingivalis and F. nucleatum) as mono-species after 2 and 24 hours, and as multispecies at day 1, 3, and 6. Sr-functionalized wafers, compared to Ti controls, were associated with statistically significant less viable cells in both mono- and multispecies tests. Number of colony forming units (CFUs) within the biofilm were significantly higher in Ti wafers, compared to Sr-functionalized wafers, for S. aureus at all time-points of evaluation and for E. coli at day 1. Gingipain activity was higher in Ti wafers compared to Sr-functionalized ones, and the qPCR showed that P. gingivalis comprised 15% of the total biofilm on Ti wafers at day 6, while it remained below detection levels at Sr-coated wafers. In Study IV, the impact of Ti surface roughness (turned vs moderately rough) on the antimicrobial effect of Sr on bacterial associated with peri-implantitis (S. oralis, P. micra, A. naeslundii, F. nucleatum, P. gingivalis, S. aureus, and E. coli), grown in different multispecies consortia, was assessed in vitro. Bacterial viability and biofilm formation, and well as, proteolytic activity of P. gingivalis were assessed at day 1, 3, and 6. Sr-functionalized surfaces were associated with statistically significant reduction in number of viable cells compared to nonfunctionalized surface at all times of investigation for all multispecies tested. Higher proteolytic activity of P. gingivalis was found at non-functionalized Ti disks compared to Sr-functionalized ones. Sr-functionalised surfaces were associated with notable growth inhibition of both E. coli and S. aureus, while P. gingivalis remined undetected at all time points of evaluation on all disks. The turned surface had a slightly higher release of Sr ion compared with the moderately rough surface in the first 24 hours, while both surfaces showed a sustained release for up to 15 days. Overall, the data generated with this series of projects indicate Sr surfaces exerts an antimicrobial potential on bacteria associated with peri-implantitis and it is worthwhile to further explore the potential of Sr-functionalized Ti in the prevention of peri-implant infections.