This document discusses the role of oral flora in oral pathologies. It notes that the normal flora can have harmful effects by aiding pathogens or competing for nutrients. It also explains that the normal flora can cause endogenous disease if they reach sites where host defenses are low. A key example is dental plaque, which consists of bacteria that accumulate on teeth and produce metabolites leading to dental diseases. The document focuses on dental caries caused mainly by Streptococcus mutans producing lactic acid, and periodontal diseases involving various bacteria damaging tissues.

1. Oral Flora and its role of in
different oral pathologies
Iyad Abou Rabii

2. Harmful Effects of the Normal Flora
1- Bacterial synergism between a member of the normal flora and a
potential pathogen.
• A member of the normal flora may supply a vitamin or some other growth factor
that a pathogen needs in order to grow. This is called cross-feeding between
microbes.
• "staph-protected infections" phenomena occurs when a penicillin-resistant
staphylococcus that is a component of the normal flora shares its drug
resistance with pathogens that are otherwise susceptible to the drug.
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3. Harmful Effects of the Normal Flora
2. Competition for nutrients Bacteria in the gastrointestinal tract must
absorb some of the host's nutrients for their own needs.
• So some nutrient(s) may be lost to the host.
• Germ-free animals are known to grow more rapidly and efficiently than
conventional animals. Incorporating antibiotics into the food of swine, cows
and poultry make animal grows faster and can therefore be marketed earlier. (a
cause of bacterial antibiotic resistance).
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4. Harmful Effects of the Normal Flora
3. The normal flora may be agents of disease. Members of the normal
flora may cause endogenous disease if they reach a site or tissue
where they cannot be restricted or tolerated by the host defenses.
Many of the normal flora are potential pathogens, and if they gain access to a
compromised tissue , or host defense is decreased, disease may result. (Candida
Albicans)
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5. Dental Plaque
 The classic biofilm that involves components of the normal flora of the oral
cavity is the formation of dental plaque on the teeth. Plaque is a naturally-
constructed biofilm, in which the consortia of bacteria may reach a
thickness of 300-500 cells on the surfaces of the teeth.
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6. Dental Plaque
 These accumulations subject the teeth and gingival tissues to high
concentrations of bacterial metabolites, which result in dental disease.
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7. Dental Plaque
 Dental plaque, consists of bacterial cells (60-70% the volume of the
plaque), salivary polymers, and bacterial extracellular products.
 These accumulations subject the teeth and gingival tissues to high
concentrations of bacterial metabolites, which result in dental and
periodontal diseases.
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8. Dental Plaque
 The dominant bacterial species in dental plaque are
 Streptococcus sanguis
 Streptococcus mutans,
Streptococcus mutans
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9. Dental Plaque
 Plaque formation is initiated by a weak attachment of the streptococcal
cells to salivary glycoproteins forming a pellicle on the surface of the
teeth.
 This is followed by a stronger attachment by means of extracellular sticky
polymers of glucose (glucans) which are synthesized by the bacteria from
dietary sugars (principally sucrose).
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10. Dental Plaque
 An enzyme on the cell surface of Streptococcus mutans,
glycosyl transferase, is involved in initial attachment of the
bacterial cells to the tooth surface and in the conversion of
sucrose to dextran polymers (glucans) which form plaque.
Dental plaque, scanning electron micrograph
illustrating the diversity of microbes in plaque.
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12. Pathologies caused by Oral Flora
 Dental caries: destruction of enamel, dentin or cementum of teeth
– bacteria in plaque produce lactic acid
Streptococcus mutans
– Lactic acid demineralizes enamel
 Periodontal disease
– Gingiva, cementum, periodontal membrane, alveolar bone
– Rich in anaerobes
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13. Dental Caries
 Dental Caries is the destruction of the enamel, dentin or cementum of
teeth due to bacterial activities.
 Caries are initiated by direct demineralization of the enamel of teeth due
to lactic acid and other organic acids which accumulate in dental plaque.
 Lactic acid bacteria in the plaque produce lactic acid from the
fermentation of sugars and other carbohydrates in the diet of the host.
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14. Dental Caries
 Streptococcus mutans and Streptococcus sanguis are most consistently
been associated with the initiation of dental caries, but other lactic acid
bacteria are probably involved as well.
 These organisms normally colonize the occlusal fissures and contact
points between the teeth, and this correlates with the incidence of decay
on these surfaces.
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15. Dental caries : Streptococcus mutans
 Streptococcus mutans in particular has a number of physiological and
biochemical properties which implicate it in the initiation of dental caries.
1. It is a regular component of the normal oral flora of humans that can form a thin
film on the tooth called the enamel pellicle.
2. It contains a cell-bound protein, glycosyl transferase, that serves an adhesin for
attachment to the tooth, and as an enzyme that polymerizes dietary sugars into
glucans that leads to the formation of plaque.
3. It produces lactic acid from the utilization of dietary carbohydrate which
demineralizes tooth enamel. S. mutans produces more lactic acid and is more
acid-tolerant than most other streptococci.
4. It stores polysaccharides made from dietary sugars which can be utilized as
reserve carbon and energy sources for production of lactic acid.
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16. Dental caries : other pathogens
 Streptococcus mutans appears to be important in the initiation of dental
caries because its activities lead to colonization of the tooth
surfaces, plaque formation, and localized demineralization of tooth
enamel.
 It is not however, the only cause of dental decay. After initial weakening of
the enamel, various oral bacteria gain access to interior regions of the
tooth.
– Lactobacilli,
– Actinomyces,
– and various proteolytic bacteria
are secondary invaders that contribute to the progression of the lesions.
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17. Periodontal Diseases
 Periodontal Diseases are bacterial infections that affect the supporting
structures of the teeth (gingiva, cementum, periodontal membrane and
alveolar bone).
 The most common form, gingivitis, is an inflammatory condition of the
gums. It is associated with accumulations of bacterial plaque in the area.
Increased populations of Actinomyces have been found, and they have
been suggested as the cause.
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18. Periodontal Diseases
 Diseases that are confined to the gingiva usually do not lead to loss of
teeth, but there are other more serious forms of periodontal disease that
affect periodontal membrane and alveolar bone resulting in tooth loss.
 Bacteria in these lesions are very complex populations consisting of
– Gram-positive organisms (including Actinomyces and streptococci)
– Gram-negative organisms (including spirochetes and Bacteroides).
 The mechanisms of tissue destruction in periodontal disease are not
clearly defined but hydrolytic enzymes, endotoxins, and other toxic
bacterial metabolites seem to be involved.
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20. Copyright notice
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Dr. Iyad Abou Rabii
Iyad.abou.rabii@qudent.edu.sa
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