A six-month, double blind, clinical study was conducted to determine the effect on supragingival calculus formation of a dentifrice containing 1.30% soluble pyrophosphate (from 2.0% tetrasodium pyrophosphate) and 1.50% of a copolymer of methoxyethylene and maleic acid, as compared to a dentifrice containing the same amount of soluble pyrophosphate but without the copolymer. This pyrophosphate/copolymer dentifrice contained the optimal ratio of pyrophosphate anion to copolymer required for obtaining a comparable anticalculus effect to a clinically proven anticalculus dentifrice containing 3.3% soluble pyrophosphate and 1.0% of a copolymer. The optimal pyrophosphate/copolymer ratio was determined by a series of in vitro laboratory and in vivo animal studies. Male and female adult subjects were stratified into three balanced groups according to baseline calculus scores. They received an oral prophylaxis and were assigned to the use of either the dentifrice containing soluble pyrophosphate and the copolymer, or to the dentifrice containing soluble pyrophosphate but without the copolymer, or to a placebo dentifrice that did not contain an anticalculus ingredient. The results of the three-month calculus examination indicated that the dentifrice containing soluble pyrophosphate and the copolymer provided a 33.66% reduction in supragingival calculus formation after an oral prophylaxis as compared to the placebo dentifrice. This reduction was statistically significant at the 99 percent level of confidence. The results of the six-month calculus examination indicated that the dentifrice containing the soluble pyrophosphate and the copolymer provided a 36.10% reduction in supragingival calculus formation after an oral prophylaxis, as compared to the placebo dentifrice. This reduction was also statistically significant at the 99% level of confidence.(ABSTRACT TRUNCATED AT 250 WORDS)