Microbial dental plaque is dense non-mineralized complex mass of colonies in a gel-like intermicrobial matrix that adheres firmly to acquired pellicle. Dental plaque may contain microorganisms other than bacteria as mycoplasmas, yeasts, protozoa and viruses. Plaque is formed in three basic steps:

1. Acquired pellicle formation: membranous layer covering the tooth made of glycoproteins that are formed minutes after tooth plaque and calculus removal.
2. Bacterial colonisation: initial attachment of bacteria to the pellicle and their multiplication and colonization
3. Plaque maturation: calcification of plaque and becoming calculus.

Days 1-2: Three bacteria involved in early plaque formation are from Viridans group of  Gram positive aerobe Streptococcus species:
1. Streptococcus mutans
2. Streptococcus mitis
3. Streptococcus. sanguinis

Days 2-4: From gram negative rods in Actinomyces species appear and are the most prevalent in early plaque formation and constitute less than 10% of total viable counts.

Days 4-7: Fusobacteria appear

Weeks 1-2: Gram negative anaerobes Vibrios and Spirochetes and they are associated with gingivitis. It is generally felt that move towards more gram negative anaerobes in plaque is associated with progression of gingivitis and periodontal disease.

If dental plaque is not removed it will play a major role in the initiation and progression of both dental caries and periodontal disease:

Dental Caries: microorganisms associated with caries development are:
- Streptococcus mutans
-Streptococcus sobrinus
-Lactobacilli
These are acid forming bacteria and they break down carbohydrates (sucrose) that comes from food and attach to the plaque and produce acid. Acid on the tooth surface drops pH down (below4.5-5.5) and thus initiates demineralization of enamel. Decomposition of enamel occurs and cavity is evident. If progressed, dentin will be demineralized and presence of Lactobacilli will be noted. Root surface caries was originally associated with Actinomyces species.
Periodontal Disease: bacteria associated with advancing periodontal disease are:
strong evidence for etiology:       - Actinobacillus actinomycetemcomitans
                                                   - Porphyromonas gingivalis
                                                   - Bacteroides forsythus
moderate evidence for etiology:  - Peptostrepcoccus micros

                                                   - Prevotella intermedia
                                                   - Fusobacterium nucleatum

© January, 2007 Copyright - Text, diagrams, figures and photographs
by B.Fidanoski- Port Credit, ON - Canada