Dental Plaque

Dental Plaque

Periodontal diseases are thought to be as a result of host bacterial imbalance. It is thought that much of the destruction that occurs in periodontal tissues is a result of an exaggerated nonprotective host response.

• It is also equally well accepted that this host response is initiated by micro-organisms present in plaque.
• Plaque is, therefore, considered the primary etiologic factor in periodontal disease. The other secondary etiologic factors potentiate the role of plaque on the host tissues.

Read And Learn More: Periodontology Important Question And Answers

Question 1. Define plaque and describe its composition and formation.
Answer:

• Dental plaque is the soft deposits that form the biofilm adhering to the tooth surface or other hard surfaces in the oral cavity, including removable and fixed restorations.
• It is classifid into supragingival plaque which is coronal to gingival margin and subgingival plaque which is apical to the gingival margin. Plaque, which is in contact with the gingival margin, is referred to as marginal plaque.

composition of plaque

• Plaque is mainly composed of microorganisms. Each milligram of wet weight of plaque consists of about 150 to 200 million bacteria.
• Other than bacteria organisms such as yeasts, mycoplasma, protozoa, and viruses are also present in small amounts along with host cells such as epithelial cells, macrophages, and leukocytes.
• These proliferating microorganisms along with host cells exist on an adherent intercellular matrix.
• This intermicrobial matrix accounts approximately for 25% of plaque volume consisting of organic and inorganic materials derived from bacterial products, saliva, and gingival crevicular fluid.
• Organic matter mainly consists of polysaccharide-protein complexes produced by plaque microorganisms. Levans, glucans, galactose, and methylpentose are some of the carbohydrates produced by microorganisms.
• Calcium and phosphorus are the main inorganic constituents of plaque along with small amounts of magnesium, potassium, and sodium.

Formation Of Dental Plaque

Dental plaque is formed in the following sequence:

Formation of an Organic Pellicle

• This involves the adsorption of positively charged salivary glycoproteins such as proline-rich proteins, Catherine, etc. to the negatively charged hydroxyapatite surfaces of teeth.
• This adsorption is made possible through electrostatic, van Der Walls, and hydrophobic forces. After its formation micro-organisms find a substrate to colonize and subsequently proliferate.

Initial Colonization

• Adhesion to the tooth surface is enhanced by the formation of the organic pellicle. The initial colonizers are mainly gram-positive organisms such as Streptococcus and Actinomyces species.
• Several cell surface binding sites have been identified in each of the early colonizers that attach them to the pellicle components, including cryptitopes which are binding sites that are exposed only after colonization has begun.

Secondary Colonization

• The initial colonizers take up all the available oxygen and carbohydrates, leading to an anaerobic, low-pH environment that favors organisms such as the bridging Fusobacterium nucleatum, organisms.
• These organisms are so-called as they adhere to the initial colonizers on one hand and to the late colonizers on the other.
• This phenomenon described as coaggregation can be seen in the early stages between F.nucleatum and A. viscosus followed by coaggregation between F. nucleatum and P.gingivalis.
• The various appearances associated with subgingival microflora have been described as “corncob”—the adherence of streptococci species to actinomyces species and the “brush border”— adherence of gram-negative rods on the surface of filamentous bacteria.
• Bacterial succession is a term used to describe the phenomenon whereby one set of organisms is replaced by a different set of organisms within the biofilm.
• This replacement is not merely a passive process as the initial colonizers provide the right environment, including anaerobiosis and metabolic substitutes for the growth of the late colonizers.

Question 2. Describe the microbial complexes.
Answer:
Socransky and Haffjee, based on their observations of bacterial plaque, classified the bacteriae involved in periodontal disease as follows:

Early Colonizers

Purple complex: Actinomyces odontolyticus, Veillonella parvula species.

Yellow complex: Streptococcus species (S. gordonii, S. intermedius, S.oralis, S. mitis, S.sanguis), Actinomycesnaeslundii, A.viscosus.

Green complex: A. Actinomycetemcomitans (serotype a), Capnocytophaga species, Eikenella corrodens.

Late Colonizers

Orange complex: P. intermedia, P.nigrescens, P. micros, F. nucleatum

Red complex: P.gingivalis, T. forsythia, T.denticola.

Question 3. Discuss the etiological role of plaque in periodontal diseases.
Answer:

The etiological role of plaque in periodontal diseases was recognized after Loe’s experimental gingivitis studies firmly established that it was involved in the initiation and progression of periodontal diseases.

Nonspecific Plaque Hypothesis

• The nonspecific plaque hypothesis proposed that the severity was associated with the quantity of plaque formed.
• This theory suggested that when the plaque content, with its toxins and breakdown products, exceeded the capacity of the host response, disease occurred.
• It was Walter Loesche in 1976 who formulated the specific plaque hypothesis.

Specific Plaque Hypothesis

According to this hypothesis, the quality and not the quantity of plaque mattered as only certain micro-organisms in plaque were thought to be pathogenic.

• When these specific bacteria increased in number, virulent factors released by them would lead to periodontal disease.
•  The close association of Aggregatibacter actinomycetemcomitans and localized aggressive
  periodontitis was often quoted as an example of this hypothesis.

Ecological Plaque Hypothesis

Marsh proposed this hypothesis on the basis that it is not isolated organisms that were responsible for periodontal disease, but the entire flora associated with the biofilm that was engaged with the disease process.

• When bacteria grow together near each other, they create biofilms that are favorable ecological niches for their survival. It is this biofilm that ultimately initiates and propagates the chronic inflammatory reaction that characterizes periodontitis.

Some of the advantages offered by the biofilm to the bacteria are:

1. Increased adhesion of bacteria to host and each other.
2. Increased availability of nutrients including optimal oxygen and pH requirements.
3. Increased resistance to antibacterial agents.
4. Facilitates exchange of genetic material between bacteria (a process called Quorum sensing) that confers individual bacteria greater pathogenicity.

Question 4. Enumerate the micro-organisms associated with periodontal health and disease.
Answer:

In clinically healthy periodontium more than 65% of the microbial population within the gingival sulci is made up of gram-positive cocci.

• Fusiform bacilli, motile rods, fiaments and spirochetes are also present. Gram-negative organisms and motile rods are seen less frequently.
• In gingivitis associated with dental plaque, there is an increase in the number of gram-negative rods, filaments, and spirochetes. Initially, Actinomyces species are more common but in chronic gingivitis gram-negative bacteria such as Fusobacterium and Veillonella make up 25% of the flora.
• In chronic periodontitis, the active sites show a striking increase in the number of gram-negative bacteria with the red complex bacteria such as P.gingivalis, T.denticola, and T. forsythia found in greater numbers along with P. intermedia, A. actinomycetemcomitans, Bacteroides species, Campylobacter rectus, Eikenella species, and other spirochetes.
• It is now recognized that perhaps the greatest difference between health and periodontal disease is the fact that health states were associated with a stable microflora while diseased states were associated with a constantly changing flora.
• In localized aggressive periodontitis the most frequently detected micro-organisms are A.actinomycetemcomitans, Capnocytophaga species, Eikenella corrodens, and other bacteria such
• Etiopathogenesis as Prevotella intermedia and Campylobacter rectus. Of these A.actinomycetemcomitans has been
  regarded as a key etiological agent:
• Generalized aggressive periodontitis is frequently associated with Porphyromonas gingivalis, Tannerella forsythia, and A. actinomycetemcomitans.

Conclusion

It has been estimated there are around 700 species of bacteria in the subgingival biofilm. Several of these species remain uncultivable to date.

• However, the recognition of biofilm formation in the disease process has offered new insights into the pathogenicity and therapeutic strategies involved in periodontal disease.