Dental Plaque

What is Dental Plaque

Dental plaque is tenaciously adherent deposits that form on the tooth surfaces. It consists of an organic matrix containing a dense concentration of bacteria.

Or

Dental plaque may be defined clinically as the structured, resilient, yellow-grayish substance that adheres tenaciously to the intra-oral hard surfaces, including removable and fixed restorations. Dental plaque is primary composed of bacteria in a matrix of salivary glycoprotein and extra-cellular polysaccharides.
It is a true biofilm and the fluid layer bordering the biofilm may have rather “stationary” sublayer and fluid layer in motion. Nutrient components may penetrate this fluid medium by molecular diffusion.
Classification:
· Supra gingival plaque – Plaque that presents at or above the gingival margin.
· Sub gingival plaque – Plaque that presents below the gingival margin.

Composition of Dental Plaque

Dental plaque consists of 20% solid and 80% water. Out of 20% solid component, there are more than 70% micro-organisms.
Dental plaque matrix is composed of –
· Organic constituents :-
1. Polysaccharides (Glucan).
2. Glycoprotiens (This basically comes from the saliva).
3. Lipid.
Inorganic constituents:-

• 1. Primary => Calcium, Phosphorus

• 2. Small amount of => Magnesium, Potassium, Sodium.

Mechanism of dental plaque formation

• Formation of pellicle on the tooth surface =>

All surfaces of the oral cavity (both hard and soft tissues) are coated with a pellicle which consists of numerous components including glycoproteins (e,g; -mucins), proline rich proteins, phospho proteins – (e.g; statherin), histidine rich proteins, enzymes (e.g; alpha- amylase), and some other molecules that can function as adhesion sites for bacteria. Pellicle on the tooth surface provides a substrate on which bacteria progressively accumulate to form dental plaque.
[In 1-24 hours, gram positive cocci and short rods appear].

• Initial adhesion and attachment of bacteria =>

The concept of microbial adhesion to surfaces as 3 stage sequence. These are –
a) Phase 1 :- Transport to the surface =>
This stage involves the initial transport of the bacterium to the teeth surface. Random contacts may occur through Brownian motion, sedimentation of micro-organisms, liquid flow and active bacterial movement.
b) Phase 2 :- Initial adhesion =>
This stage results in an initial, reversible adhesion of the bacterium, initiated by the interaction between the bacterium and the surface.
c) Phase 3 :- Attachment =>
After initial adhesion, a firm enchorage between bacterium and surface will be established by specific interactions. The bonding between bacteria and pellicle is mediated by specific extra-cellular proteinaceous components of the organism and complementary receptors (i.e; Proteins, glycoproteins, polysaccharides) on the surface. Gram positive facultative micro-organisms such as actinomyces and streptococcus colonize on the pellicle surface. These gram positive cocci and rods co-aggregate and multiply.
[2-4 days rods and filamentous micro-organisms appear and the number of cocci is reduced. 6-10 days vibrios and spirochetes appear and there is relative increase in size of the gram negative anaerobic population].

• Colonization and plaque maturation:

Both streptococci and actionmycetes are facultative anaerobes and doubling times for microbial populations during the first 4 hours of development are less than 1hour. These two groups of primary colonizers are taught to prepare a favorable environment for later colonizers which have more fastidious growth requirements like ( Prevotella intermedia, Prevotella loescheii, Fusobacterium nucleatum, Porphyromonas gingivalis) adheres to the cell that have alredy in a plaque mass as they do not initially colonize in the clean teeth surfaces.
As, plaque ages, heterogenicity increases and more gram negative sticky anaerobic bacteria such as Porphyromonas gingivalis, Capnocytophagea colonized secondarily and plaque matures.