Microbiology of Periodontal Diseases

Microbiology of Periodontal Diseases

• Periodontal diseases are a complex issue involving the host, oral environment, and treatment.
• A profound knowledge of periodontal microbiology is necessary to understand and manage these diseases.
• There are different types of tooth deposits that influence periodontal disease: dental plaque, materia alba, and calculus.
• Dental plaque is a soft biofilm that adheres to teeth and restorations.
• Materia alba is a soft accumulation of bacteria and tissue debris, easily removable.
• Calculus is a hard deposit formed by mineralized dental plaque.

Learning Objectives

• Understand tooth deposits, their formation, and implications for disease.
• Recognize bacterial complexes and families involved in periodontal disease.
• Understand bacterial interactions in various periodontal diseases.
• Correlate periodontal treatment modalities with microbial reasons.

Bacterial Classification

• Gram-negative bacteria are predominantly found in subgingival/periodontal/periimplant pockets at different timeframes after birth.
• Gram-positive bacteria are often found in the initial stages in the mouth, for a period before and after birth..
• Additional types of microorganism exists and are present in the mouth; in addition to bacteria.

Six Major Ecosystems

• Intraoral and supragingival hard surfaces (teeth, implants, restorations, prostheses)
• Subgingival regions adjacent to hard surfaces (periodontal/periimplant pockets).
• Buccal/palatal epithelium and the epithelium of the floor of the mouth.
• Dorsum of the tongue
• Tonsils
• Saliva

Human Oral Microbiota

• Commensals
• Symbiotic species
• Pathogenic species.

Composition of Dental Plaque

• 70% Microorganisms (mostly bacteria: >500 strains).
• 30% Intercellular Matrix (organic and inorganic materials).

Organic Materials

• Glycoproteins (derived from saliva, pellicle component).
• Polysaccharides (produced by bacteria, commonly dextran).
• Albumin (from crevicular fluid).
• Lipids (membrane debris, host cells, and food debris).

Inorganic Materials

• Calcium and phosphorus (main components).
• Sodium, potassium, and fluoride (trace amounts).
• Derived from saliva, gingival crevicular fluid, and fluoridated toothpaste.

Bacterial Lifestyles

• Free-floating (planktonic)
• Attached to a surface forming a biofilm community.

Bacterial Biofilm Communities

• A biofilm is a well-organized community of bacteria adhering to surfaces and embedded in an extracellular slime layer.
• More than 99% of all bacteria on Earth live as attached bacteria.
• Biofilms are found on medical/dental devices (e.g., implants).
• Formed via bacterial interactions with a solid surface. Physical & physiological interactions among species take place within the microbial mass then.
• Biofilms show increased resistance to antimicrobials. The limited diffusion of substances into the matrix, slow cell growth rate within the biofilm environment. Altered bacterial properties resulting from growth on surfaces make the bacteria more resistant.

Plaque Formation Phases

• Pellicle Formation (initial layer coating the tooth surface).
• Initial Colonization (bacteria predominantly gram-positive).
• Secondary Colonization (non-initial bacteria adhering to/coaggregating with existing colonies).
• Plaque Maturation (further growth and colonization of microorganisms, transition to anaerobic environment).

Formation of Dental Plaque

• May be readily visualized on teeth after 1-2 days without oral hygiene.
• Appears as white, grayish, or yellow.
• Typically observed on the gingival third of the tooth surface.
• Forms preferentially in cracks, pits, fissures, under overhanging restorations, around malaligned teeth.
• Location and rate depend on oral hygiene, diet, salivary composition, and saliva flow rate
• Absence of oral hygiene - plaque continues to accumulate.
• The process involves 3 phases (1-formation of pellicle, 2-initial colonization, 3-secondary colonization, 4-plaque maturation).

Plaque Index

• Method for measuring plaque amount.
• Plaque is stained using disclosing tablets (or other similar methods).
• The amount of plaque is calculated based on the number of stained sites vs. total number of sites.

Microbiologic Specificity of Periodontal Diseases

• Nonspecific Plaque Hypothesis
• Specific Plaque Hypothesis
• Ecological Plaque Hypothesis

Microorganisms Associated with Specific Periodontal Diseases

• Periodontal Health (Gram-positive facultative bacteria; Streptococcus and Actinomyces species)
• Gingivitis (almost equal proportions of gram-positive and gram-negative bacteria)
• Localized Aggressive Periodontitis (90% A. actinomycetemcomitans)
• Pregnancy Gingivitis/Associated with Pregnancy (P. intermedia using steroids as growth factors)
• Chronic Periodontitis (high percentage anaerobic gram-negative bacteria; P. gingivalis, P. intermedia, F. nucleatum, and B. forsythus. Herpesviruses EBV-1 and HCMV have been linked to this)
• Abscesses of the Periodontium (F. nucleatum, P. intermedia, P. gingivalis, P. micros, B. forsythus)

Controlling Dental Plaque Biofilm

• Mechanical removal is the most effective method currently available.

Different Plaque Regions and Associated Diseases

• Supragingival plaque - calculus and caries, gingivitis
• Marginal plaque - calculus and caries, gingivitis
• Subgingival plaque- calculus and caries, soft tissue destruction
• Tooth-associated plaque
• Tissue-associated plaque

Key Points

• Importance of subgingival niche (ecosystem).
• Gingivitis VS Periodontitis.
• Plaque is the primary factor for gingivitis and periodontitis.
• Shifts in microbial communities as periodontitis progresses.