Bacterial Properties Involved in Evasion of Host Defense Mechanisms

Bacteria have evolved various strategies to evade the host's immune defenses, allowing them to persist and cause disease. Understanding these mechanisms is crucial for developing effective treatments and preventive measures against bacterial infections, particularly in the context of periodontal disease. This lecture will explore the bacterial species involved, their properties, and the biological effects of these properties on host defense mechanisms.

Host Defense Mechanisms and Bacterial Evasion Strategies

1. Specific Antibody Evasion

   • Bacterial Species:
     • Porphyromonas gingivalis
     • Prevotella intermedia
     • Prevotella melaninogenica
     • Capnocytophaga spp.
   • Bacterial Property:
     • IgA- and IgG-degrading proteases
   • Biologic Effect:
     • Degradation of specific antibodies, which impairs the host's ability to mount an effective immune response against these bacteria.

2. Evasion of Polymorphonuclear Leukocytes (PMNs)

   • Bacterial Species:
     • Aggregatibacter actinomycetemcomitans
     • Fusobacterium nucleatum
     • Porphyromonas gingivalis
     • Treponema denticola
   • Bacterial Properties:
     • Leukotoxin: A toxin that can induce apoptosis in PMNs.
     • Heat-sensitive surface protein: May interfere with immune recognition.
     • Capsule: A protective layer that inhibits phagocytosis.
     • Inhibition of superoxide production: Reduces the oxidative burst necessary for bacterial killing.
   • Biologic Effects:
     • Inhibition of PMN function, leading to decreased bacterial killing.
     • Induction of apoptosis (programmed cell death) in PMNs, reducing the number of immune cells available to fight infection.
     • Inhibition of phagocytosis, allowing bacteria to evade clearance.

3. Evasion of Lymphocytes

   • Bacterial Species:
     • Aggregatibacter actinomycetemcomitans
     • Fusobacterium nucleatum
     • Tannerella forsythia
     • Prevotella intermedia
   • Bacterial Properties:
     • Leukotoxin: Induces apoptosis in lymphocytes.
     • Cytolethal distending toxin: Affects cell cycle progression and induces cell death.
     • Heat-sensitive surface protein: May interfere with immune recognition.
     • Cytotoxin: Directly damages immune cells.
   • Biologic Effects:
     • Killing of mature B and T cells, leading to a weakened adaptive immune response.
     • Nonlethal suppression of lymphocyte activity, impairing the immune response.
     • Impairment of lymphocyte function by arresting the cell cycle, leading to decreased responses to antigens and mitogens.
     • Induction of apoptosis in mononuclear cells and lymphocytes, further reducing immune capacity.

4. Inhibition of Interleukin-8 (IL-8) Production

   • Bacterial Species:
     • Porphyromonas gingivalis
   • Bacterial Property:
     • Inhibition of IL-8 production by epithelial cells.
   • Biologic Effect:
     • Impairment of PMN response to bacteria, leading to reduced recruitment and activation of neutrophils at the site of infection.

Keratinized Gingiva and Attached Gingiva

The gingiva is an essential component of the periodontal tissues, providing support and protection for the teeth. Understanding the characteristics of keratinized gingiva, particularly attached gingiva, is crucial for assessing periodontal health.

Keratinized Gingiva

1. Definition:

   • Keratinized gingiva refers to the gingival tissue that is covered by a layer of keratinized epithelium, providing a protective barrier against mechanical and microbial insults.

2. Areas of Keratinized Gingiva:

   • Attached Gingiva:
     • Extends from the gingival groove to the mucogingival junction.
   • Marginal Gingiva:
     • The free gingival margin that surrounds the teeth.
   • Hard Palate:
     • The roof of the mouth, which is also covered by keratinized tissue.

Attached Gingiva

1. Location:

   • The attached gingiva is the portion of the gingiva that is firmly bound to the underlying alveolar bone.

2. Width of Attached Gingiva:

   • The width of attached gingiva varies based on location and can increase with age and in cases of supraerupted teeth.

3. Measurements:

   • Greatest Width:
     • Found in the incisor region:
       • Maxilla: 3.5 mm - 4.5 mm
       • Mandible: 3.3 mm - 3.9 mm
   • Narrowest Width:
     • Found in the posterior region:
       • Maxillary First Premolar: 1.9 mm
       • Mandibular First Premolar: 1.8 mm

Clinical Significance

• Importance of Attached Gingiva:

  • The width of attached gingiva is important for periodontal health, as it provides a buffer zone against mechanical forces and helps maintain the integrity of the periodontal attachment.
  • Insufficient attached gingiva may lead to increased susceptibility to periodontal disease and gingival recession.

• Assessment:

  • Regular assessment of the width of attached gingiva is essential during periodontal examinations to identify potential areas of concern and to plan appropriate treatment strategies.

Bone grafting is a critical procedure in periodontal and dental surgery, aimed at restoring lost bone and supporting the regeneration of periodontal tissues. Various materials can be used for bone grafting, each with unique properties and applications.

A. Osseous Coagulum

• Composition: Osseous coagulum is a mixture of bone dust and blood. It is created using small particles ground from cortical bone.
• Sources: Bone dust can be obtained from various anatomical sites, including:
  • Lingual ridge of the mandible
  • Exostoses
  • Edentulous ridges
  • Bone distal to terminal teeth
• Application: This material is used in periodontal surgery to promote healing and regeneration of bone in areas affected by periodontal disease.

B. Bioactive Glass

• Composition: Bioactive glass consists of sodium and calcium salts, phosphates, and silicon dioxide.
• Function: It promotes bone regeneration by forming a bond with surrounding bone and stimulating cellular activity.

C. HTR Polymer

• Composition: HTR Polymer is a non-resorbable, microporous, biocompatible composite made from polymethyl methacrylate (PMMA) and polyhydroxymethacrylate.
• Application: This material is used in various dental and periodontal applications due to its biocompatibility and structural properties.

D. Other Bone Graft Materials

• Sclera: Used as a graft material due to its collagen content and biocompatibility.
• Cartilage: Can be used in certain grafting procedures, particularly in reconstructive surgery.
• Plaster of Paris: Occasionally used in bone grafting, though less common due to its non-biological nature.
• Calcium Phosphate Biomaterials: These materials are osteoconductive and promote bone healing.
• Coral-Derived Materials: Natural coral can be processed to create a scaffold for bone regeneration.

Connective Tissue of the Gingiva and Related Cellular Components

The connective tissue of the gingiva, known as the lamina propria, plays a crucial role in supporting the gingival epithelium and maintaining periodontal health. This lecture will cover the structure of the lamina propria, the types of connective tissue fibers present, the role of Langerhans cells, and the changes observed in the periodontal ligament (PDL) with aging.

Structure of the Lamina Propria

1. Layers of the Lamina Propria:

   • The lamina propria consists of two distinct layers:
     1. Papillary Layer:
        • The upper layer that interdigitates with the epithelium, containing finger-like projections that increase the surface area for exchange of nutrients and waste.
     2. Reticular Layer:
        • The deeper layer that provides structural support and contains larger blood vessels and nerves.

2. Types of Connective Tissue Fibers:

   • The lamina propria contains three main types of connective tissue fibers:

     1. Collagen Fibers:
        • Type I Collagen: Forms the bulk of the lamina propria and provides tensile strength to the gingival fibers, essential for maintaining the integrity of the gingiva.
     2. Reticular Fibers:
        • These fibers provide a supportive network within the connective tissue.
     3. Elastic Fibers:
        • Contribute to the elasticity and flexibility of the gingival tissue.

   • Type IV Collagen:

     • Found branching between the Type I collagen bundles, it is continuous with the fibers of the basement membrane and the walls of blood vessels.

Langerhans Cells

1. Description:

   • Langerhans cells are dendritic cells located among keratinocytes at all suprabasal levels of the gingival epithelium.
   • They belong to the mononuclear phagocyte system and play a critical role in immune responses.

2. Function:

   • Act as antigen-presenting cells for lymphocytes, facilitating the immune reaction.
   • Contain specific granules known as Birbeck’s granules and exhibit marked ATP activity.

3. Location:

   • Found in the oral epithelium of normal gingiva and in small amounts in the sulcular epithelium.
   • Absent from the junctional epithelium of normal gingiva.

Changes in the Periodontal Ligament (PDL) with Aging

1. Aging Effects:
   • With aging, several changes have been reported in the periodontal ligament:
     • Decreased Numbers of Fibroblasts: This reduction can lead to impaired healing and regeneration of the PDL.
     • Irregular Structure: The PDL may exhibit a more irregular structure, paralleling changes in the gingival connective tissues.
     • Decreased Organic Matrix Production: This can affect the overall health and function of the PDL.
     • Epithelial Cell Rests: There may be a decrease in the number of epithelial cell rests, which are remnants of the Hertwig's epithelial root sheath.
     • Increased Amounts of Elastic Fibers: This change may contribute to the altered mechanical properties of the PDL.

Platelet-Derived Growth Factor (PDGF)

Platelet-Derived Growth Factor (PDGF) is a crucial glycoprotein involved in various biological processes, particularly in wound healing and tissue repair. Understanding its role and mechanisms can provide insights into its applications in regenerative medicine and periodontal therapy.

Overview of PDGF

1. Definition:

   • PDGF is a glycoprotein that plays a significant role in cell growth, proliferation, and differentiation.

2. Source:

   • PDGF is carried in the alpha granules of platelets and is released during the process of blood clotting.

3. Discovery:

   • It was one of the first growth factors to be described in scientific literature.
   • Originally isolated from platelets, PDGF was found to exhibit mitogenic activity specifically in smooth muscle cells.

Functions of PDGF

1. Mitogenic Activity:

   • PDGF stimulates the proliferation of various cell types, including:
     • Smooth muscle cells
     • Fibroblasts
     • Endothelial cells
   • This mitogenic activity is essential for tissue repair and regeneration.

2. Role in Wound Healing:

   • PDGF is released at the site of injury and plays a critical role in:
     • Promoting cell migration to the wound site.
     • Stimulating the formation of new blood vessels (angiogenesis).
     • Enhancing the synthesis of extracellular matrix components, which are vital for tissue structure and integrity.

3. Involvement in Periodontal Healing:

   • In periodontal therapy, PDGF can be utilized to enhance healing in periodontal defects and promote regeneration of periodontal tissues.
   • It has been studied for its potential in guided tissue regeneration (GTR) and in the treatment of periodontal disease.

Clinical Applications

1. Regenerative Medicine:

   • PDGF is being explored in various regenerative medicine applications, including:
     • Bone regeneration
     • Soft tissue healing
     • Treatment of chronic wounds

2. Periodontal Therapy:

   • PDGF has been incorporated into certain periodontal treatment modalities to enhance healing and regeneration of periodontal tissues.
   • It can be used in conjunction with graft materials to improve outcomes in periodontal surgery.

Theories Regarding the Mineralization of Dental Calculus

Dental calculus, or tartar, is a hard deposit that forms on teeth due to the mineralization of dental plaque. Understanding the mechanisms by which plaque becomes mineralized is essential for dental professionals in managing periodontal health. The theories regarding the mineralization of calculus can be categorized into two main mechanisms: mineral precipitation and the role of seeding agents.

1. Mineral Precipitation

Mineral precipitation involves the local rise in the saturation of calcium and phosphate ions, leading to the formation of calcium phosphate salts. This process can occur through several mechanisms:

A. Rise in pH

• Mechanism: An increase in the pH of saliva can lead to the precipitation of calcium phosphate salts by lowering the precipitation constant.
• Causes:
  • Loss of Carbon Dioxide: Bacterial activity in dental plaque can lead to the loss of CO2, resulting in an increase in pH.
  • Formation of Ammonia: The degradation of proteins by plaque bacteria can produce ammonia, further elevating the pH.

B. Colloidal Proteins

• Mechanism: Colloidal proteins in saliva bind calcium and phosphate ions, maintaining a supersaturated solution with respect to calcium phosphate salts.
• Process:
  • When saliva stagnates, these colloids can settle out, disrupting the supersaturated state and leading to the precipitation of calcium phosphate salts.

C. Enzymatic Activity

• Phosphatase:
  • This enzyme, released from dental plaque, desquamated epithelial cells, or bacteria, hydrolyzes organic phosphates in saliva, increasing the concentration of free phosphate ions and promoting mineralization.
• Esterase:
  • Present in cocci, filamentous organisms, leukocytes, macrophages, and desquamated epithelial cells, esterase can hydrolyze fatty esters into free fatty acids.
  • These fatty acids can form soaps with calcium and magnesium, which are subsequently converted into less-soluble calcium phosphate salts, facilitating calcification.

2. Seeding Agents and Heterogeneous Nucleation

The second theory posits that seeding agents induce small foci of calcification that enlarge and coalesce to form a calcified mass. This concept is often referred to as the epitactic concept or heterogeneous nucleation.

A. Role of Seeding Agents

• Unknown Agents: The specific seeding agents involved in calculus formation are not fully understood, but it is believed that the intercellular matrix of plaque plays a significant role.
• Carbohydrate-Protein Complexes:
  • These complexes may initiate calcification by chelating calcium from saliva and binding it to form nuclei that promote the deposition of minerals.

Clinical Implications

1. Understanding Calculus Formation:

   • Knowledge of the mechanisms behind calculus mineralization can help dental professionals develop effective strategies for preventing and managing calculus formation.

2. Preventive Measures:

   • Maintaining good oral hygiene practices can help reduce plaque accumulation and the conditions that favor mineralization, such as stagnation of saliva and elevated pH.

3. Treatment Approaches:

   • Understanding the role of enzymes and proteins in calculus formation may lead to the development of therapeutic agents that inhibit mineralization or promote the dissolution of existing calculus.

4. Research Directions:

   • Further research into the specific seeding agents and the biochemical processes involved in calculus formation may provide new insights into preventing and treating periodontal disease.