The effect of a combination of copper and hexetidine on plaque formation and the amount of copper retained by dental plaque bacteria

Abstract

Zn⁺⁺ in combination with hexetidine exerts a synergistic plaque inhibition. Studies in our laboratory on the mechanism of this effect suggested that Cu ⁺⁺ and hexetidine may have a similar combination effect. This hypothesis was tested in vivo on a human test panel in a double-blind crossover study. The amount of Cu⁺⁺ retained by plaque bacteria in vitro was also evaluated. Seven volunteers rinsed with the solutions for 1 min twice daily for 5 days. The test solutions were H₂O, 1.0 mM CuSO₄, 2.0 mM hexetidine, and the last two in combination. During the test period no oral hygiene was allowed, and sucrose-containing chewing gum was used to enhance plaque formation. The plaque index scores after rinsing with the combination were significantly (p < 0.05) lower than those of the other solutions. The effect of hexetidine onCu⁺⁺ retention in plaque bacteria was evaluated in plaque samples (n = 3) grown anaerobically overnight in PPLO medium. The bacteria were washed five times, digested in concentrated HNO₃, and Cu⁺⁺ determined by atomic absorption. The presence of hexetidine resulted in a significantly greater amount of Cu ⁺⁺ retained by bacteria at all CuSO₄ concentrations. It is suggested that the nonpolar nature of the hexetidine molecule enables Cu⁺⁺ bound to hexetidine to pass into the bacterial cell. Within the cell, Cu ⁺⁺ can interfere with bacterial metabolism, giving a reduction in plaque growth.