Evaluation of ion release and the recharge ability of glass-ionomer cement containing BioUnion filler using an in vitro saliva-drop setting assembly

•An in vitro saliva-drop setting was assembled to evaluate ion-release properties.•GIC containing BioUnion filler releases Zn2+ and F− under acidic conditions.•Re-uptake of Zn2+ and F− in the GIC could be obtained.•Release of Zn2+ from the GIC after recharging hinders biofilm formation. A glass-ionomer cement (GIC) containing BioUnion filler has been reported to release Zn2+ under acidic conditions and to inhibit oral bacteria on its surface. However, previous results are based on in vitro experiments under static conditions. This study aimed to assemble an in vitro saliva-drop setting to simulate in vivo conditions of the oral cavity and to investigate the ion releasing and recharging properties of the GIC containing BioUnion filler. The effective concentrations of Zn2+ and F− against Streptococcus mutans and saliva-derived multi-species biofilms were determined. Artificial saliva was dropped on the GIC containing BioUnion filler using the in vitro saliva-drop setting assembly and was periodically replaced with acetic acid. Ion release/recharge properties were investigated by measuring the release concentrations of Zn2+ and F−. The concentration of Zn2+ released from the BioUnion filler-containing GIC during seven days with repeated exposure to acid could be maintained at the level to inhibit S. mutans and saliva-derived multi-species biofilm formation. Moreover, the BioUnion filler-containing GIC could be recharged with Zn2+ and F− by the application of a tooth gel containing Zn2+ and F−. The release concentration of Zn2+ after recharging was significantly higher than the effective concentration of Zn2+ to hinder S. mutans and saliva-derived multi-species biofilm formation on material surfaces. The GIC containing BioUnion filler was shown to have the potential to inhibit biofilm formation in the oral cavity. In addition, recharging Zn2+ and F− would further enhance the effect of the GIC containing BioUnion filler.