Section 4-2. Dental enamel possesses hexagonal crystalline structure. Streptococcus mutans is the natural enemy

The surface of teeth is covered with a layer called as dental enamel. This corresponds to the skin in our body, contributing to protection of our body. Teeth are the hardest tissues in the body. Although they seem like stones and not the living body, it might be a misunderstanding. When one piece of teeth is investigated under microscope, they have a crystalline structure mainly consisting of hydroxyapatite, called as an enamel pillaret.
Its matured crystalline occurs as a long plate-like susbstance with sexangular section like amethyst and topaz (Figure 53). In the similar manners as we inspire the air and expire the air with ample carbon dioxide, the surface of dental enamel absorbs calcium, phosphorus and fluoride ion from the saliva surrounding the dental enamel. Between teeth and saliva, there is a dynamic exchange of inorganic ions. In other words, the dental enamel breathes. Once dental caries occurs, recalcification is available as the self-repairing system if it is in an initial stage.
When Streptococcus mutans dissolves the dental enamel, substantial defect occurs in the teeth, resulting in emergence of dental caries. This is due to acids which are produced by decomposition of sucrose by Streptococcus mutans. This bacterium produces glucan, as a viscous substance consisting of polysaccharides on the surface of teeth, together with production of acids to dissolve teeth. This viscous glucan plays a role as the barrier to protect Streptococcus mutans from bactericidal effects and bacterial eradication effects of the saliva, thereby allowing survival of lots of this bacterium on the surface of teeth, and forming the biofilm (Figure 54). The white layer on the surface of teeth which contains such a glucan and Streptococcus mutans is called as plaque. Because of this barrier, acids which are synthesized by this bacterium from sugar also contribute to maintenance of highly acidic conditions which are preferable to growth of this bacterium.
These plaque, glucan and biofilm cannot be removed from the teeth surface by gurgle. However, teeth are suffocated by presence of this barrier which is prepared by Streptococcus mutans. The suffocated dental enamel covered with glucan for a long period of time results in being dissolved by acids and leading to death.
Such a death is observed as decayed teeth (Please refer to Figure VIII). Commonly, it is called as dental caries. However, if we remove these matrix corresponding to the skeleton of the dental enamel at the early stage of its collapse thereby resuming dental respiration, such an injured matrix can be resuscitated by the so-called re-calcification, known as the self-repairing function. This re-calcification means a series of mechanisms that fine cavity caused by acid-inducing dissolving phenomena is again filled with calcium, phosphorus and fluoride ion to repair this eroded part much more firmly than before.
As described above, our teeth also breathe like varieties of living bodies. Unless the plaque and glucan sticking onto the surface of the teeth are removed by means of tooth brush, toothpick or floss, teeth die of suffocation.
Glucan is too sticky to be unable to be removed unless thorough cleaning is employed. The biting surface of teeth has fissure which is a deep and narrow ditch, whereby it is impossible to clean the inside of this ditch. This indicates that sweeping the ditch has a limitation. As the natural consequence, we must map out any countermeasures other than physical cleanings to eradicate decayed teeth by eliminating all Streptococcus mutans from our mouth. This issue is extremely important and therefore, we wish to discuss it in the Chapter 7.