Some aspects of the dynamics of Cu and Zn retained in plaque as related to their effect on plaque pH.

The effect of glucose on acid production in dental plaque was measured in vivo after oral rinses with CuSO4 (1.0 mM) or Zn (Ac)2 (20 mM) and compared with the retention of the metals. Plaque samples were analyzed for copper and zinc by neutron activation analysis. A rinse with the cooper salt solution significantly depressed acid formation in plaque for a period of 6 h whereas a rinse with the zinc solution was effective for 2 h. Plaque concentrations of the metals increased from less than 75 p.p.m. to more than 1000 p.p.m. 2 h after a rinse with the metal salts. Twelve hours after a rinse the mean plaque concentrations were 190 p.p.m. Cu or 358 p.p.m. Zn respectively. Reducing the pH of the copper sulfate solution from 5.7 to 2.0 yielded lower Cu concentrations in plaque 2 h after a rinse, indicating lower initial retention. The results clearly demonstrate a high and long lasting retention of metal ions in dental plaque and their biological effect in this environment.