Objective: We sought to develop a facile in vitro model for assessing the potential of agents to interfere with mineral formation in dental plaque and foster removal of calcium from this model of calculus. Methods: Bacterial species known to be good plaque biofilm formers were grown in complex medium on steel wires by the technique of serial wire transfer. Cultures included some that mineralize. Wire-adherent plaques were incubated in a complex mineralizing solution. The disappearance of calcium from that solution and the appearance of calcium salts in the plaques were monitored by calcium-specific stain and calcium analysis. Plaque amounts were quantified by both dry weight and protein analyses. Incubation of such plaques with sodium tripolyphosphate (STPP) at various concentrations, durations, and frequencies, consistent with conditions of human use in toothpaste, was evaluated for its effect on calcium levels. Results: Calcium salt formation occurred in some of the bacterial plaques. STPP fostered the disappearance of calcium from the mineralizing solution and it inhibited the appearance of relatively insoluble calcium salts in those plaques capable of depositing calcium salts. If calcium salts were initially deposited into those plaques, STPP removed a large proportion of them. The conditions were consistent with those of ordinary human use of toothpaste. Conclusions: A model has been developed for the formation of in vitro calcium deposits in plaque that mimics formation of dental calculus. A commonly used anti-calculus agent (STPP) inhibits relatively insoluble calcium salt deposition in such in vitro plaques and it fosters removal of previously formed calcium salt deposits from those plaques. Supported by a contract with GlaxoSmithKline.