Multiphasic analyses of the interaction between cariogenic polysaccharide and tooth enamel

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It has been known that a bacteria, Streptococcus sobrinus, found in human saliva converts sucrose to a sticky polysaccharide called α-glucan. This glucan called α-glucan is composed of (1→3)-α-linked D-glucose in the backbone sequence on which (1→6)-α-linked D-glucose is attached as a side residue, and it is involved in dental plaque formation by sticking on the surface (tooth enamel composed of hydroxyapatite) of human teeth. In the plaque, the bacteria transforms sucrose to lactic acid which dissolves hydroxyapatite (decalcification of the enamel) and, consequently it causes of dental caries. We have studied to analyze the cause of dental caries by various physicochemical strategies as follows.1. The conformational analyses of α-glucan by using an X-ray diffraction coupled with an energy calculation indicated that the backbone (1→3)-α-D-glucan takes up an extended two-fold helix (a zigzag structure). Some energetically preferable conformations of the glucan were proposed.2. Spectroscopic (infrared, fluorescence and circular dichroism) studies on the interaction between α-glucan and a hydroxyapatite crystal of pseudohexagonal polymorph, which is likened to tooth enamel, did not detect the presence of any strong bond such as hydrogen bonding.3. Examinations of the effects of some caries preventers on the dissolution of hydroxyapatite to lactic acid indicated that two chitin derivatives (carboxymethyl and ethylene glycol chitins) decrease the soubility.