• Perinatal transmission (90%)
• Window phase: HBsAg ↓, anti-HBs ↑
• Infectivity: HBsAg + HBeAg
• First marker post-infection: HBsAg
• IgM anti-HBc = acute infection
• Reverse transcriptase → P gene
  | Hepatitis C | Most chronic & linked to liver disease
  | Hepatitis A | Prophylaxis: Human IgG
  | Hepatitis E | Most epidemic-prone in India
  | Councilman bodies | Seen in acute viral hepatitis

• Junctional Epithelium: Attached to enamel via hemidesmosomes; to connective tissue via external basal lamina.
• Corneocyte Formation: Keratinohyalin granules disappear, forming filaggrin.
• Langerhans Cells: Suprabasal level; antigen-presenting with Birbeck granules.
• Keratinization: Oral epithelium is 0.2 – 0.3 mm thick; may be keratinized or parakeratinized.

Erythema Multiforme

• Characteristics: Erythema multiforme presents with "target" or "bull's eye" lesions, often associated with:
  • Etiologic Factors:
    • Herpes simplex infection.
    • Mycoplasma infection.
    • Drug reactions (e.g., sulfonamides, penicillins, phenylbutazone, phenytoin).

Smoking

• Pack years = Packs/day × Years of smoking

Diabetes

• Causes collagen cross – linking via AGEs formation

AIDS

• Most common oral lesion: Candidiasis
• Most common oral malignancy: Kaposi sarcoma

Junctional Epithelium

The junctional epithelium (JE) is a critical component of the periodontal tissue, playing a vital role in the attachment of the gingiva to the tooth surface. Understanding its structure, function, and development is essential for comprehending periodontal health and disease.

Structure of the Junctional Epithelium

1. Composition:

   • The junctional epithelium consists of a collar-like band of stratified squamous non-keratinized epithelium.
   • This type of epithelium is designed to provide a barrier while allowing for some flexibility and permeability.

2. Layer Thickness:

   • In early life, the junctional epithelium is approximately 3-4 layers thick.
   • As a person ages, the number of epithelial layers can increase significantly, reaching 10 to 20 layers in older individuals.
   • This increase in thickness may be a response to various factors, including mechanical stress and inflammation.

3. Length:

   • The length of the junctional epithelium typically ranges from 0.25 mm to 1.35 mm.
   • This length can vary based on individual anatomy and periodontal health.

Development of the Junctional Epithelium

• The junctional epithelium is formed by the confluence of the oral epithelium and the reduced enamel epithelium during the process of tooth eruption.
• This fusion is crucial for establishing the attachment of the gingiva to the tooth surface, creating a seal that helps protect the underlying periodontal tissues from microbial invasion.

Function of the Junctional Epithelium

• Barrier Function: The junctional epithelium serves as a barrier between the oral cavity and the underlying periodontal tissues, helping to prevent the entry of pathogens.
• Attachment: It provides a strong attachment to the tooth surface, which is essential for maintaining periodontal health.
• Regenerative Capacity: The junctional epithelium has a high turnover rate, allowing it to regenerate quickly in response to injury or inflammation.

Clinical Relevance

• Periodontal Disease: Changes in the structure and function of the junctional epithelium can be indicative of periodontal disease. For example, inflammation can lead to increased permeability and loss of attachment.
• Healing and Repair: Understanding the properties of the junctional epithelium is important for developing effective treatments for periodontal disease and for managing healing after periodontal surgery.