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 mu g/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.

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. 

Aim: to explore the antimicrobial potential of strontium (Sr) coated wafers against multiple bacteria associated with per-implant infections, in both mono and multi-species forms.

Materials and methods: Sr-coated and uncoated Ti wafers were tested for bactericidal effect and biofilm growth inhibition against several bacteria, either grown as a mono-species or as a culture of multi-species, using bacterial viability assay and plate counting method. Mono-species test performed over a rocking platform and evaluated after 2 and 24 hours, while multi-species antimicrobial test evaluation was carried out at day 1, 3 and 6. The impact of Sr coating on the total percentage of P. gingivalis in the multi-species biofilm, using qPCR, and gingipain activity were also assessed.

Results: Sr-coated wafers were associated with statistically significant less viable cells for both mono- and multi-species tests compared to Ti controls. Number of colony forming units (CFUs) were significantly higher in Ti wafers, for S. aureus, at all time-points of evaluation and at day 1 for E. coli within the biofilm compared to Sr-coated wafers. Gingipains activity were higher in Ti wafers compared to Sr-coated ones, and qPCR showed that P. gingivalis percentage was 15% of the total biofilm of Ti wafers at day 6, while it remained below detection levels at Sr-coated wafers.

Conclusion: Sr coating displayed promising antimicrobial potential against bacteria associated with peri-implantitis grown either as mono-species or in a multi-species consortium.

Aim: To study the effect of Sr coated Ti disks with smooth and moderately rough surface on biofilm formation, gingipain activity, inhibition of growth of Porphyromonas gingivalis, Escherichia coli and Staphylococcus aureus using amulti-species model mimicking the subgingival environment, and to explore the pattern of Sr ion release.

Materials and methods: the antimicrobial potential of Sr coated disks, i.e., smoothSr (S-Sr) and rough Sr (R-Sr) was investigated using a five species bacterial model and compared to uncoated Ti disks, i.e., smooth Ti (S-Ti) and rough Ti (RTi)at 3 different time point: 1, 3 and 6 days. Biofilm formation was investigated using LIVE/DEAD BacLight staining and confocal scanning laser microscopy and image analysis software, while inhibition of growth of P. gingivalis, E. coli and S. aureus was measured using qPCRr or growth on selective agar medium. Gingipain activity was measured using fluorescent substrate BIKKAM-16. Sr ion release from Sr coated disks was investigated up to 15 days.

Results: S-Sr and R-Sr were associated with statistically significant reduction in number of viable cells compared to S-Ti and R-Ti at all different times of investigation for all multispecies tested (p < 0.001). Higher proteolytic activity associated with uncoated Ti disks compared to Sr coated disks in the P. gingivalis multispecies test at day 6. Utilizing qPCR, P. gingivalis remined undetected at all time points of evaluation for all disks, while in plate counting method, coated surfaces were associated with notable growth inhibition of both E.coil and S.aureus, using MacConkey and 110-plates, respectively. S-Sr had slightly higher release of Sr ion in the first 24 hours than R-Sr, while both Sr coated surfaces sustained stable release up to 15 days.

Conclusion: In the present study, Sr coated surface, i.e., S-Sr and R-Sr, demonstrated great antimicrobial potential against multiple bacterial associated with peri-implant infection and provided a possible strategy for Ti implants infection prevention.