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Aspects of dental plaque formation with special reference to colloid-chemical phenomena.

In order to investigate factors of importance for plaque formation and the rate of plaque formation 133 randomly selected individuals went through a 3-day period of plaque accumulation. From these individuals one group of "heavy" and one group of "light" plaque formers were selected for further studies. These subjects were investigated with reference to clinical, biochemical, biophysical and microbiological variables, that in the literature have been suggested to influence plaque formation. The collected data were analysed statistically both by comparisons between the two groups and by multiple regression. In the comparative analyses there were only minor differences between the groups, and no single studied variable was considered as the only explanation to the great difference in the amount of plaque formed after 3 days between "heavy" and "light" plaque formers. The multiple regression showed that the initial bacterial colonization of tooth surfaces was dependent on the clinical wettability of tooth surfaces, the saliva-induced aggregation of oral bacteria and finally the relative salivary flow conditions around the tooth surfaces where the bacterial samples were collected. On basis of these results, it was suggested that saliva and oral bacteria could at least partly be looked upon as being a biological colloid system system. Further studies were designed to investigate whether oral bacteria could be regarded as colloid particles or not, and to study the properties of saliva as a colloid suspending medium. These studies showed that bacteria suspended in different salt solutions were dependent on pH, ionic concentration and the valency of the cations in the solutions to be able to aggregate. The aggregating capacity further seemed to be specific for different bacterial species and strains. Addition of saliva from "heavy" and "light" plaque formers influenced the colloid stability of bacteria suspended in water in different ways. Saliva from "light" plaque formers gave a lower colloid stability in suspensions of a plaque-forming bacterium (Streptococcus sanguis) as compared to the addition of saliva from "heavy" plaque formers. No such differences were observed in suspensions of S. salivarius, which is normally not a plaque-forming bacterium. The results indicate that colloid-chemical processes might be involved in bacterial attachment to tooth surfaces, and that initial bacterial colonization of tooth surfaces at least partly follow general biophysical laws.