Objectives: It is known that phosphoryl group links covalently to a certain starch molecule. The purposes of this study were to examine the inhibitory effects of phosphoryl oligosaccharides (POs) against artificial plaque accumulation, pH underneath the plaque and enamel demineralization by mutans streptococci using artificial mouth system. Methods: Flat surface electrode with a holder bearing four bovine enamel slabs was set upside down in a vessel and was kept at 37°C. A suspension of S. sobrinus 6715 or S. mutans MT8148 cells in PBS, HI broth containing 1% sucrose and PBS or PBS containing 5% POs were supplied on the electrode by peristaltic pump. All procedures were carried out under aseptic conditions. Changes in pH underneath the artificial plaque were continuously recorded. Enamel demineralization was evaluated by measuring difference of microhardness of enamel before and after experiments. Results: The pH values of control (1% sucrose) began to decrease after around 5 and 10h, and reached a plateau (pH 4.4 ) after 16 and 20h in S. sobrinus and S. mutans, respectively. When 1% sucrose and 5% POs were supplied, pH values were 5.8 and 5.5 in S. sobrinus and S. mutans, respectively. The turbidity of cells (OD at 500nm/mm2) accumulated on test enamel surface of control and experiment (POs) after 16h in S. sobrinus were 0.070±0.012 and 0.016±0.007, respectively. That after 20h in S. mutans were 0.018±0.006 and 0.001±0.001, respectively. Mean differences of microhardness of enamels in control and experiment in S. sobrinus were 240±16 and 19±10, respectively. That in S. mutans were 250±5 and 54±9, respectively. Conclusions: POs inhibited artificial plaque accumulation and enamel demineralization in the presence of sucrose suggesting that POs might partially inhibit cariogenic potential of sucrose under these conditions.

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