Inhibition of plaque growth by zinc salts

Certain metal salts inhibit the growth of dental plaque. The effect of zinc salts was investigated because of contradictory reports in the literature. Using cultures of human plaque, artificial dental plaques were grown in vitro on aluminium strips. The effect of various zinc salts was examined by treating the strips intermittently with solutions of the salts during the period of growth. The action of mouthwashes containing zinc salts in vivo on plaque growth was determined in human volunteers.
All the water-soluble zinc salts that were tested gave a similar concentration-dependent inhibition of plaque growth in vitro . The effectiveness of the treatment was reduced by increasing the time allowed for growth after the final application of zinc.
Solutions of zinc (17–19 mM) as the citrate or phenolsulphonate salt, gave about 30% reduction in the extension of plaque along the gingival margin in vivo over 16 hours. Subjects with high rates of plaque growth with the placebo mouthwash were most affected by zinc salts. Increasing the zinc concentration to 30 mM did not further increase the activity. Previous reports of low activity of zinc against plaque growth in vivo are explained by too low a concentration of zinc or too low a frequency of application. The results confirm that zinc salts, including zinc citrate, inhibit the growth of plaque in vivo and in vitro .