unit eight caries and perio

8/3/2019 Unit Eight Caries and Perio

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Oral microbiology

Microbes and Dental

Disease


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Normal Flora of the Human Oral

Cavity The presence of nutrients, epithelial debris and

secretions makes the mouth a favorable habitat

for a great variety of bacteria.

Oral bacteria include mainly streptococci,

lactobacilli, staphylococci, and a great number of

anaerobes, especially bacteroides.

Hundreds of different bacteria have beenidentified in the oral cavity although this does not

imply that they are not transients.


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Normal flora development

At birth the oral cavity is composed solely of thesoft tissues of the lips, cheeks, tongue andpalate, which are kept moist by the secretions of

the salivary glands. At birth the oral cavity is sterile but rapidly

becomes colonized from the environment,particularly from the mother in the first feeding.

Streptococcus salivarius is dominant and maymake up 98% of the total oral flora until theappearance of the teeth (6 - 9 months inhumans).


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Normal flora development

The creation of the gingival sulcus area

(supporting structures of the teeth)

increases the habitat for the variety ofanaerobic species found.

The complexity of the oral flora continues

to increase with time, and bacteroides and

spirochetes colonize around puberty.


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Oral cavity diseases

Several oral bacteria have been implicatedin diseases of the oral cavity, including

dental caries and periodontal diseases

such as gingivitis and periodontitis.


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Dental plaque

Dental plaque, which is material adhering to theteeth, consists of bacteria(60-70% the volume ofthe plaque), salivary protein, and bacterialextracellular products.

Plaque is a naturally-constructed biofilm, inwhich the colony of bacteria may reach athickness of 300-500 cells on the surfaces of theteeth.

These accumulations subject the teeth andgingival tissues to high concentrations ofbacterial metabolites, which result in dentaldisease.


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Bacterial toxicity

Bacteria involved in dental caries andperiodontitis produce three forms of toxins:

1- protein toxins (Exotoxins) which work asextracellular enzymes

2- Endotoxins, which arelipopolysaccharides in the Gram-negative

cell wall;3- products of bacterial metabolism (e.g.

metabolites) which may be toxic.


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Gingivitis bacteriology

Porphyromonas gingivalis.

A common bacterium found in periodontalinfections.

Virulence factors of the bacterium includeendotoxin, and production of extracellularenzymes.

The main bacteria found to be responsible in

Periodontitis is Actinobacillus actinomycetem-comitans


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Gingivitis


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Dental plaque formation

Plaque formation is initiated by a weakattachment of the streptococcal cells to pellicleon the surface of the teeth.

This is followed by a stronger attachment bymeans of extracellular slime layer which aresynthesized by the bacteria from dietary sugars

An enzyme on the cell surface of Streptococcusmutans, glycosyl transferase, is involved in initial

attachment of the bacterial cells to the toothsurface and in the conversion of sucrose whichform plaque.( Page 51-- box 5-2 some importantperiodontopathogens)


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Dental Caries

Dental Caries is the destruction of the enamel,dentin or cementum of teeth due to bacterialactivities.

Caries are initiated by direct demineralization ofthe enamel of teeth due to lactic acid and otherorganic acids which accumulate in dentalplaque.

B

acteria in the plaque produce lactic acid fromthe fermentation of sugars and othercarbohydrates in the diet of the host.


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Dental Caries

Streptococcus mutans has mostconsistently been associated with theinitiation of dental caries, but other lactic

acid bacteria are probably involved aswell.

These organisms normally colonize theocclusal fissures and contact pointsbetween the teeth, and this correlates withthe incidence of decay on these surfaces.


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unit eight caries and perio

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