The effects of experimental variations in dietary sugar intake and oral hygiene on the biochemical composition and pH of free smooth-surface and approximal plaque.

The biochemical compositions of free smooth-surface and approximal plaque were compared after 48 hours in the presence and absence of twice-daily toothbrushing and during ingestion of either high- or low-sugar diets in ten young adults. In addition, the effect of a single sugar intake on the pH of both types of plaque was investigated. The results confirmed previously reported differences in biochemical composition between free smooth-surface and approximal plaque, the concentrations of inorganic ions and carbohydrate fractions being generally lower in the approximal sample after all experimental regimens. The concentrations of calcium and phosphorus were doubled on the low-sugar diet compared with the high-sugar diet in both types of plaque. A significant decrease in carbohydrate concentrations was observed in free smooth-surface plaque in subjects on the low-sugar diet, but not in approximal plaque. Little variation was observed in the biochemical composition which could be attributed to the presence or absence of toothbrushing. The pH in free smooth-surface plaque was lower than that in approximal plaque five minutes after a sugar intake, but the situation was reversed two hours later. The results indicate that differences in composition and pH between free smooth-surface and approximal plaque are associated with reduced access to salivary and dietary influences due to diffusion limitation in the deeper layers of plaque.