Antimicrobial Properties of Strontium Functionalized Titanium Surfaces for Oral Applications, A Systematic Review

Abstract

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.

New strontium-based coatings show activity against pathogenic bacteria in spine infection

“…Therefore, the newly developed Sr-TCP coatings seem to induce a delay in cell growth, but not a killing effect against planktonic cells. Similar with our results, previous studies investigating the antibacterial properties of strontium revealed a limited early inhibition of the bacterial growth ( Alshammari et al, 2021a ). The authors attributed this observation to a slow kinetic of release of Sr ions in the medium during bacterial growth.…”

“…Strontium is a chemical element that is widely used for various applications in different industries. Strontium has been used as co-metal in the functionalization of silver-modified titanium implant surfaces thanks to its ability to lower the cytotoxic effect of silver towards the host cells without altering the antimicrobial properties and to promote osseointegration and bone regeneration ( Zhao et al, 2020 ; Alshammari et al, 2021a ; Baheiraei et al, 2021 ). Recently, some indications on the antibacterial properties of this metal have been reported, indicating strontium as a promising alternative to traditional antibiotics ( Alshammari et al, 2021a ; 2021b ).…”

Antibacterial and Cytocompatible: Combining Silver Nitrate with Strontium Acetate Increases the Therapeutic Window

“…Consequently, a great interest has risen in substances with dual functionality, biofilm control as well as cell compatibility. In a recent study, the antimicrobial potential of strontium hydroxide against pathogenic oral bacteria was demonstrated [ 23 ], and related reviews reported the antimicrobial effects of functionalized surfaces with silver, strontium, or combinations of both [ 13 , 33 ]. Therefore, the aim of the present study was to systematically describe a therapeutic window for the application of silver and strontium salts on tissue cells and pathogenic bacteria of the oral cavity for the first time.…”

“…In the same mono-culture setups, the cytocompatibility and antibacterial potential of strontium acetate were also tested. Despite the beneficial osteogenic effects of strontium, which have been extensively investigated, only a few studies evaluated the bactericidal effect of strontium against pathogenic oral bacteria [ 23 , 33 ]. In the present study, a minimum inhibitory concentration of SrAc (5 mg/mL) against A. actinomycetemcomitans after 24 h of incubation was defined.…”

Polyelectrolyte‐Cation Complexes Using PAsp‐Sr Complexes Induce Biomimetic Mineralization with Antibacterial Ability

“…[17] Sr-doped HAp exhibits antibacterial activity due to the release of strontium ions, which might inhibit bacterial activities, including growth and reproduction, cell metabolism, and cell wall synthesis. [18][19][20][21] Fluorine also possesses some antibacterial properties, while the exact mechanisms remain unclear. [18,22] Moreover, strontium has a synergistic antibacterial effect with fluorine.…”