Collection and biochemical analysis of human dental plaque from the approximal tooth surfaces and comparison with plaque from free smooth surfaces.

The composition of approximal plaque was compared with that normally collected from the free smooth surfaces in investigation of 45 males aged 11-14 years and 75 females aged 13 years. Statistically significant differences in calcium, inorganic and organic phosphorus, magnesium, fluoride and carbohydrate were observed between free smooth-surface and approximal plaque. The concentrations were always lower in the approximal sample, ranging from 55 to 70 per cent of those in free smooth-surface plaque. A subsequent comparison in 12 students indicated that the concentration of total lipids in approximal plaque was about twice that of free smooth-surface plaque, a difference which could explain the quantitative disparity in total composition between the two types of plaque in the studies with children. The differences are consistent with approximal plaque having reduced access to a range of environmental factors due to diffusion limitation in its deeper layers.