GSE
Bacterial flora In dental plaque, dental caries and periodontal disease
Bacterial flora In dental plaque, dental caries and periodontal
disease
Dental plaque, dental caries and periodontal disease
in humans result from actions initiated by normal bacterial flora as they have developed a costly symbiosis with humans
Dental Plaque
Dental Plaque is bacteria-laden material adhering
to the teeth - which consists of:
• Bacterial cells (60-70% the volume
of the plaque)
• Salivary polymers
• Bacterial extracellular products.
- Plaque
is a naturally-constructed biofilm, with bacteria reaching a thickness of up to
300-500 cells on the surfaces of the teeth. Such accumulations
subject the teeth and gingival tissues to high concentrations of bacterial metabolites,
which result in dental disease.
- With no
contest, the dominant
Streptococcus sanguis
and Streptococcus
mutans
- Plaque
formation is initiated by weak attachment of
streptococcal
cells to salivary glycoproteins. Forming a thin film (pellicle)
on the surface of the teeth. Next, a stronger attachment is formed by extracellular
sticky polymers of glucose (glucans) synthesized by the bacteria from dietary sugars
(mainly sucrose).
- Attachment
of S. mutans
and the formation of glucans is mediated by glycosyl transferase.
This enzyme located on the cell surface of
Streptococcus mutans
is involved in both initial attachment of the bacterial cells to the
tooth surface and in the conversion of sucrose to dextran and levan polymers (glucans)
which form the extracellular matrix of plaque. Attachment can be prevented by the
specific antibody to the enzyme.
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 plaque produce lactic acid by fermenting the host's dietary sugars
and other carbohydrates.
-
Streptococcus mutans is considered the most likely culprit
associated with the initiation of dental caries - but other lactic acid bacteria
are probably involved as well. These organisms normally colonize the occlusal fissures
(see diagram) and contact points between the teeth, correlating with decay on these
surfaces.
Cross section of a tooth illustrating the various structural
regions susceptible to colonization or attack by microbes
Dental Plaque
Periodontal Diseases are bacterial infections affecting
teeth support structures (gingiva, cementum, periodontal membrane
and alveolar bone).
- Gingivitis is an
inflammatory condition of the gums - associated with bacterial plaque build-up
in the affected area. Increased presence of
ACTINO MYCES
are suggested as the cause. Diseases confined to the gum do not
usually lead to loss of teeth.
- More serious forms of periodontal
disease affect periodontal membrane and alveolar bone - and can result
in tooth loss. Bacteria in these lesions are consist of
GRAM-POSITIVE organisms (including
ACTINO MYCES
and
streptococcI)
and 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.
FREQUENTLY ENCOUNTERED BACTERIA IN PLAQUE, DENTAL CARIES, GINGIVITIS
AND PERIODONTITIS
BACTERIUM
Plaque
Dental caries
Gingivitis
Periodontitis
Streptococcus
sanguis
++
++
++
+
S. mutans
++
++
0
0
S. salivarius
0
0
0
0
ACTINO MYCES
VISCOSIS
+
+
++
+
A. ISRAELI
+
+
++
++
LACTO BACILLUS
sp.
+
+
0
0
PROPIONIBACTERIUM ACNES
0
+
+
++
Bacteroides sp.
0
0
+
++
Selenomonas sputagena
0
0
+
++
Large spirochetes
0
0
0
++
++ = Frequently encountered in high proportions;
+ = Frequently encountered in low to moderate proportions;
0 = Sometimes encountered in low proportions or not detectable.
Modified from Davis, et al.: Microbiology. 4th ed.
J. B. Lippincott. Philadelphia, 1990.
Reference
Kenneth Todar, PhD.
Online Textbook of
BacteriologyIn the GI Tract
