The role of sucrose in cariogenic dental biofilm formation--new insight

Abstract

Dental caries is a biofilm-dependent oral disease, and fermentable dietary carbohydrates are the key environmental factors involved in its initiation and development. However, among the carbohydrates, sucrose is considered the most cariogenic, because, in addition to being fermented by oral bacteria, it is a substrate for the synthesis of extracellular (EPS) and intracellular (IPS) polysaccharides. Therefore, while the low pH environment triggers the shift of the resident plaque microflora to a more cariogenic one, EPS promote changes in the composition of the biofilms' matrix. Furthermore, it has recently been shown that the biofilm formed in the presence of sucrose presents low concentrations of Ca, P(i), and F, which are critical ions involved in de- and remineralization of enamel and dentin in the oral environment. Thus, the aim of this review is to explore the broad role of sucrose in the cariogenicity of biofilms, and to present a new insight into its influence on the pathogenesis of dental caries.

Figure 1

Schematic illustration of a cariogenic biofilm formation in the presence of fermentable sugars (A) or in the presence of sucrose (B); EPS enhances the cariogenic potential of the biofilm formed in the presence of sucrose (adapted from Marsh, 1994).

Figure 2

Schematic representation of the first, second, third, fourth and fifth hypotheses, respectively. First hypothesis: Constant low pH caused by sucrose fermentation would release ions from mineral deposits, which could diffuse to saliva, and promote dental plaque with lower inorganic ion concentrations. However, after 10-12 hrs, there would have been enough time for the mineral ions, which had been lost to saliva, to be replaced by the simple law of mass action. Second hypothesis: Enamel could have taken up ions from biofilm fluid during pH-cycling. After 12 hrs, the biofilms would have been again saturated with these ions. Third hypothesis: Schematic representation adapted from Rose et al. (1996). Binding to bacterial cell wall is another reservoir of minerals. When the pH falls, the minerals are released from biofilm. After the pH is increased, the biofilm is saturated again with the ions from saliva. Fourth hypothesis: Bacterial density. Note that, in the second circle, the density of bacteria is lower, since polysaccharides occupy a large volume of the biofilm. Fifth hypothesis: Low concentrations of specific ion-binding proteins. It has been suggested that biofilm formed in the presence of sucrose shows fewer calcium-binding sites for proteins.

Figure 3

Two-dimensional gel electrophoresis of dental biofilm formed in the absence (A) and presence (B) of sucrose (20 μg of proteins). Isoelectric focusing with pH range 4-7 and PAGE (8-18%). The gels were silver-stained. Spots were excised for in-gel digestion and analyzed by mass spectrometry (MALDITOF). The fingerprints were analyzed in Mascot and Prospector program with the NCBInr database. Arrows show calcium-binding proteins present only in biofilm formed in the absence of sucrose (A) when compared with biofilm formed in the presence of sucrose (B).