Dental Plaque and Calculus: Composition, Formation, and Pathogenesis

Posted on Aug 1, 2024 in Biology

Dental Plaque

Definition

Dental plaque is a variable but specific structural entity resulting from the colonization and growth of microorganisms of various species and strains embedded in an extracellular matrix.

Classification

• Supragingival
  • Coronal
  • Marginal
  • Fissural
• Subgingival
  • Tooth associated
  • Tissue associated
  • Unattached

Supragingival Plaque

Supragingival plaque is a stratified organization, multilayered accumulation of bacteria. Gram-positive cocci and short rods predominate on the tooth surface, while Gram-negative rods, filaments, and spirochetes predominate on the outer surface. Supragingival plaque can lead to calculus formation, caries, and marginal plaque-induced gingivitis.

Subgingival Plaque

Subgingival plaque is characterized by gram-positive rods and cocci, including Streptococcus mitis, S. sanguis, A. viscosus, Actinomyces naeslundii, and Eubacterium spp. In deeper parts of the pocket, filamentous organisms become fewer. The apical border is separated from the junctional epithelium by a layer of host leukocytes, and the bacteria show an increased concentration of gram-negative rods.

Composition

• Water: 80-85% plaque mass; 50% intracellular, 35% matrix
• Cells: primarily bacteria, 1 gm (wet weight) = 10¹¹ bacteria
• Non-bacterial: Mycoplasma spp, yeasts, protozoa, viruses
• Host cells: epithelial cells, macrophages, and leucocytes
• Matrix: 20-30% plaque mass
  • Organic
    • Carbohydrates: Dextrans, levans, polysaccharides, galactose
    • Lipids
    • Proteins: Albumin, glycoproteins
    • Misc: extracellular bacterial products, cell remnants, food
  • Inorganic
    • Calcium
    • Phosphorus/phosphate
    • Na, Cl, F

Plaque Formation

Plaque formation involves the following steps:

1. Formation of the Dental Pellicle
2. Initial adhesion and attachment
   1. Phase 1: Transport to the surface
   2. Phase 2: Initial adhesion
   3. Phase 3: Attachment
   4. Phase 4: Colonization
3. Colonization and plaque maturation

Four Modes of Attachment

1. Attachment by means of an organic pellicle.
2. Mechanical locking into the surface irregularities such as resorption lacunae and caries
3. Close adaptation of calculus undersurface depressions to the gently sloping mounds of the unaltered cementum surface
4. Penetration of calculus bacteria into cementum

Comparison of Supragingival and Subgingival Plaque

Biofilm

Biofilm is a matrix-enclosed bacterial population adherent to each other and/or to surfaces and inter-surfaces (Costerton 2000).

Properties

• Microcolonies of bacterial cells (15–20% by volume), non-randomly distributed in a shaped matrix or glycocalyx (75–80% volume).
• Presence of voids or water channels…Nutrients diffuse from the water channel to the microcolony rather than from the matrix…
• At low shear force, the colonies are shaped like towers or mushrooms.

Plaque Hypotheses

• Nonspecific Plaque Hypothesis
• Specific Plaque Hypothesis: States that only certain plaque is pathogenic, and its pathogenicity depends on the presence of or increase in specific microorganisms
• Ecological Plaque Hypothesis

Calculus

Calculus consists of mineralized bacterial plaque that forms on the surfaces of natural teeth and dental prosthesis

Supragingival Calculus

Supragingival calculus frequently forms on the lingual surfaces of mandibular anterior teeth and the buccal surfaces of the first molars in both the mandible and maxilla. These sites are close to the orifices of salivary ducts.

Subgingival Calculus

Subgingival calculus is also site-specific, although it is less apparent than its supragingival counterpart. It is higher on the lingual than on the buccal surfaces, with the lingual surfaces of the lower first molars and the buccal surfaces of the mandibular anterior teeth and maxillary molar teeth having the greatest amount of subgingival calculus.

Composition

Dental calculus is primarily composed of mineral as well as inorganic and organic components. Supragingival and subgingival calculus contain 37% and 58% mineral content by volume, respectively.

Theories of Calculus Formation

PHYSIOCHEMICAL THEORY/ BOOSTER CONCEPT

(Prinz 1928), Mineral precipitation results from a local rise in the degree of saturation of calcium and phosphate ions, which may be brought about in several ways:

1. Loss of carbon dioxide
2. Formation of ammonia by dental plaque bacteria
3. Protein degradation during stagnation

EPITACTIC THEORY/ HETEROGENEOUS NUCLEATION / SEEDING THEORY

Seeding agents induce small foci of calcification that enlarge and coalesce to form a calcified mass. The seeding agents in calculus formation are not known, but it is suspected that the intercellular matrix of plaque plays an active role. The carbohydrate protein complexes may initiate calcification by removing calcium from the saliva (chelation) and binding with it to form nuclei that induce subsequent deposition of minerals.