Does strontium play a role in the cariostatic activity of glass ionomer? Strontium diffusion and antibacterial activity

Objectives: The aim of this work was to evaluate the activity of strontium ions on the main pathogens of the oral flora. The leaching of strontium from resin modified glass ionomer cements (RMGIC) was evaluated together with its uptake by superficial dental enamel. Methods: The antibacterial activity was measured by the growth inhibition method following exposure of supra- and sub-gingival bacteria to a range of strontium concentrations (0.19 mol l(-1), 0.37 mol l(-1), 0.74 mol l(-1) and 1.11 mol l(-1)). Strontium concentrations were analyzed chemically and migration at 5 mu m. and 15 mu m depths was quantified by microprobe following Fuji Ortho LC application on the vestibular enamel of extracted teeth. Results: Strontium was found in appreciable amounts (0.8 wt.%) in superficial enamel, but in insignificant concentrations deeper in. At the same time, 8% fluoroapatite was formed in the enamel. Under our experimental conditions, strontium had no significant antibacterial activity; only one log reduction of activity was observed at the highest concentrations tested. Conclusions: RMGIC releases strontium ions which are rapidly exchanged for calcium ions in the superficial enamel. No significant antibacterial activity was observed for strontium ions alone at the concentrations considered. However synergistic effects with fluoride could promote antibacterial activity. (C) 2009 Elsevier Ltd. All rights reserved.