You can read the part 2 of most common disease that causes loss of teeth, before reading the 3rd part.
The cariogenicity of S. mutans depends on properties summarized below.
Cariogenic properties of Streptococcus mutans
• It produces lactic acid from sucrose
• It can live at a pH as low as 4.2
• It forms large amounts of extracellular, sticky and insoluble glucan plaque matrix
• It adheres to pellicle and contributes to plaque formation
This scanning electronmicrograph of plaque shows the large number of filamentous organisms and, in addition, many cocci clustered amongst them.
Bacterial Plaque
Plaque is a tenaciously adherent deposit that forms on tooth surfaces. It consists of an organic matrix containing a dense concentration of bacteria. In microbiological terms, plaque is a biofilm. Biofilms consist of a hydrated viscous phase formed from bacteria and their extracellular polysaccharide matrices. In such a film, molecules and ions exist in concentrations that can be widely different from those of the surrounding fluid phase (saliva).
Bacteria in biofilms can also exhibit cooperative activity and behave differently from the same species in isolation in a culture medium. As a consequence, a biofilm may be resistant to antimicrobials or to immunological defences to which the individual bacteria are normally sensitive. Bacterial plaque must therefore be regarded as a living entity and not as a mere collection of bacteria. In particular, the ability of dental plaque to concentrate and retain acid was recognized long before the special properties of biofilms were discovered.
This scanning electron micrograph at higher power shows cocci attached to filamentous organisms to produce the corn-cob type of arrangement sometimes seen in plaque
Clinically, bacterial plaque is a tenaciously adherent deposit on the teeth. It resists the friction of food during mastication, and can only be readily removed by toothbrushing. However, neither toothbrushing nor fibrous foods will remove plaque from inaccessible surfaces or pits.
Plaque becomes visible, particularly on the labial surfaces of the incisors, when toothbrushing is stopped for 12-24 hours. It appears as a translucent film with a matt surface that dulls the otherwise smooth and shiny enamel. It can be made obvious when stained with disclosing agents. Little plaque forms under conditions of starvation but it forms rapidly and abundantly on a high-sucrose diet.
In stagnation areas where it is undisturbed, plaque bacteria can form acid from sugars over sufficiently long periods as to attack tooth surfaces. Adhesion of bacteria to the teeth from which they would otherwise be washed away is an essential requirement for the colonization of enamel. Attachment depends on complex mechanisms and depends on such molecules as glucans and/or glucosyltransferase. Components of plaque which act as adhesion receptors include a group of proline-rich proteins (PRPs) from the saliva.
Stages of formation of bacterial plaque
If teeth are thoroughly cleaned by polishing with an abrasive, plaque quickly re-forms.
Acid production in plaque
Sucrose diffuses rapidly into plaque, and acid production quickly follows. These changes have been measured directly in the human mouth using microelectrodes in direct contact with plaque. It has been shown by this means that, after rinsing the mouth with a 10% glucose solution, the pH falls within 2-5 minutes, often to a level sufficient to decalcify enamel. Even though no more sucrose may be taken and the surplus is washed away by the saliva, the pH level remains at a low level for about 15-20 minutes; it returns only gradually to the resting level after about an hour.
The rapidity with which the pH falls is a reflection of the speed with which sucrose can diffuse into plaque and the activity of the concentration of enzymes produced by the great numbers of bacteria in the plaque. The slow rate of recovery to the resting pH — a critical factor in caries production.
