Two mechanisms of oral malodor inhibition by zinc ions

Abstract

Objectives

The aim of this study was to reveal the mechanisms by which zinc ions inhibit oral malodor.

Material and Methods

The direct binding of zinc ions to gaseous hydrogen sulfide (H₂S) was assessed in comparison with other metal ions. Nine metal chlorides and six metal acetates were examined. To understand the strength of H₂S volatilization inhibition, the minimum concentration needed to inhibit H₂S volatilization was determined using serial dilution methods. Subsequently, the inhibitory activities of zinc ions on the growth of six oral bacterial strains related to volatile sulfur compound (VSC) production and three strains not related to VSC production were evaluated.

Results

Aqueous solutions of ZnCl₂, CdCl₂, CuCl₂, (CH₃COO)₂Zn, (CH₃COO)₂Cd, (CH₃COO)₂Cu, and CH₃COOAg inhibited H₂S volatilization almost entirely. The strengths of H₂S volatilization inhibition were in the order Ag+ > Cd₂+ > Cu₂+ > Zn₂+. The effect of zinc ions on the growth of oral bacteria was strain-dependent. Fusobacterium nucleatum ATCC 25586 was the most sensitive, as it was suppressed by medium containing 0.001% zinc ions.

Conclusions

Zinc ions have an inhibitory effect on oral malodor involving the two mechanisms of direct binding with gaseous H₂S and suppressing the growth of VSC-producing oral bacteria.

Keywords
Antimicrobial activity; Chemical binding; Hydrogen sulfide; Oral malodor; Zinc ions