Microscopic Anatomy of the Periodontium Chapter 2

Microscopic Anatomy of the Periodontium

Learning Objectives

  • Cells of Periodontal Tissues: Discuss types of cells present.

  • Tissue Types: Explain the four types of tissues in the human body.

  • Extracellular Matrix:

    • Describe its composition and function.

    • Identify locations of keratinized and non-keratinized cells, basal layers, epithelial basal lamina, connective tissue, and blood vessels.

  • Cell Functions: Describe purposes and forms of functions.

  • Epithelial-Connective Tissue Interface: Features and functions.

  • Connective Tissue Components: Define major components and their characteristics.

  • Gingival Epithelium Structure: Outline features and compare keratinized versus non-keratinized areas.

  • Junctional Epithelium Characteristics: Describe health indicators and structural features.

Video Reviews and Aids

  • Periodontal Tissues Review Video:

    helpful for reinforcing content.

  • Key Video Aids: Focused on topics like desmosomes vs. hemidesmosomes, epithelial vs. connective tissue, and keratinization.

Microscopic Anatomy Overview

  • Histology: Study of microscopic features of tissues.

  • Tissue Definition:

    • Defined as a group of interconnected cells performing similar functions.

    • Composed of various cells and extracellular elements forming organs.

Cell Organization

  • Hierarchy of Life Forms:

    • Cells: Smallest units able to function independently.

    • Tissues: Formed by groups of cells.

    • Organs: Composed of multiple tissue types.

    • Systems: Groups of organs functioning together.

Tissue Types

  • Four Basic Tissue Types:

    • Epithelial: Covers surfaces and lines cavities.

    • Connective: Binds and supports other tissues.

    • Muscle: Facilitates movement.

    • Nervous: Transmits impulses for coordination.

Extracellular Matrix (ECM)

  • Description: Mesh-like network surrounding cells.

  • Function: Supports cells and provides a framework for cell migration and interaction.

  • Composition:

    • Mainly ground substance and fibrous proteins.

    • Variability in abundance between epithelial and connective tissues:

    • Sparse in epithelial tissue (primarily the basal lamina).

    • More abundant in connective tissues.

Epithelial Tissue Anatomy

  • Function: Constitutes the outer surface of the body and lines body cavities.

  • Composition: Comprised mainly of packed cells with minimal ECM.

  • Characteristics:

    • Stratified squamous epithelium in skin and oral mucosa.

Keratinization Process

  • Definition: Process where surface epithelial cells become waterproof and tougher.

  • Location: Found in high-friction areas, like palms and soles.

  • Types of Cells:

    • Keratinized: Lack nuclei, form a tough protective layer.

    • Nonkeratinized: Contain nuclei, serve as cushions in tissue.

Blood Supply to Epithelial Cells

  • Characteristics: Epithelial tissues are avascular (lack blood vessels).

  • Nourishment: Received through diffusion from blood vessels in underlying connective tissues.

Connective Tissue Anatomy

  • Function: Fills spaces between tissues, supports, and binds other tissues.

  • Composition:

    • Sparse cellular makeup (fibroblasts, phagocytes, neutrophils, lymphocytes).

    • Contains abundant extracellular substances such as cementum, dentin, alveolar bone, pulp.

Epithelial-Connective Tissue Interface

  • Description: Site of interaction between epithelial and connective tissues; may be smooth or wavy.

  • Wavy Interface Features: Increase adhesion surface area, assist in resisting mechanical force, and improve nourishment absorption from connective tissue.

  • Basal Lamina: Aids epithelial attachment to adjacent structures; includes both basal and reticular lamina.

Morphologic Patterns of Interface

  • Common Patterns: Tight interdigitation resembling clasped hands.

    • Epithelial Ridges (Rete Pegs): Extensions into connective tissue improving adhesion and nutrient uptake.

    • Gingival Stippling: Associated with healthy periodontium, correlating with rete pegs presence.

  • Smooth Interface: Lacking interdigitating structures; observed in healthy sulcular and junctional epithelium.

Functions of the Epithelial-Connective Tissue Interface

  • Enhances adhesion to connective tissue through increased surface area.

  • Supports the skin against mechanical forces and secures nourishment channels.

Junctions in Epithelial Cells

  • Desmosomes: Mechanically link cells and provide resistance against stress.

  • Hemidesmosomes: Attach epithelial cells to the basal lamina, crucial in gingival epithelium.

Cell Composition Recap

  • Epithelial Tissues: Predominantly cellular with minimal extracellular matrix.

  • Connective Tissue: Few cells with a substantial extracellular matrix.

  • Blood Supply: Epithelial tissues lack blood supply, whereas connective tissues possess a rich blood supply.

Gingival Epithelium Anatomy

  • Type: Specialized stratified squamous epithelium accommodating the wet oral environment.

  • Anatomical Regions: Consists of three areas: oral epithelium, sulcular epithelium, and junctional epithelium.

    • Oral Epithelium: Covers the outer surface from the crest of the gingival margin to the mucogingival junction; keratinized.

    • Sulcular Epithelium: Single layer, nonkeratinized, lining the sulcus.

    • Junctional Epithelium: Attaches gingiva to the tooth, thin, and semipermeable.

Oral Epithelium Detailed Structure

  • Layer Structure:

    • Basal Cell Layer (Stratum Basale): Provides a foundation for regeneration.

    • Prickle Cell Layer (Stratum Spinosum): Offers structural integrity.

    • Granular Cell Layer (Stratum Granulosum): Contributes to keratinization.

    • Keratinized Cell Layer (Stratum Corneum): The outermost protective layer.

Sulcular Epithelium Characteristics

  • Structure: Thin, nonkeratinized epithelium, continuous with the oral epithelium.

  • Fluid Permeability: Allows gingival crevicular fluid passage into the sulcus; flow varies by health status.

  • Attachment: Joins connective tissue with a smooth interface, lacking interdigitation.

Junctional Epithelium Functions

  • Attachment Function: Binds gingiva to tooth surface, acting as a barrier against bacteria.

  • Structural Features:

    • Length: 0.71 to 1.35 mm.

    • Thickness: 15 to 30 cells at the coronal end; tapers to 4-5 cells at the apical end.

Junctional Epithelium Importance

  • Erupting teeth disrupt the epithelial barrier; junctional epithelium provides closure to prevent infection.

Junctional Epithelium Composition

  • Cells: Dense with minimal extracellular matrix; contains hemidesmosomes and basal lamina.

  • Attachments: Secures to tooth via hemidesmosomes; remains inconspicuous under light microscopy.

Microscopic Anatomy of Gingival Connective Tissue

  • Function: Provides structural integrity and attachment of gingiva to root cementum and alveolar bone (also called lamina propria).

  • Cells: Composed of a small percentage of cells (5%); includes fibroblasts, mast cells, and immune cells.

Extracellular Matrix of Gingival Connective Tissue

  • Composition:

    • 55% to 65% collagen fibers.

    • 30% to 35% gel-like matrix material providing structural support.

Supragingival Fiber Bundles

  • Purpose: Reinforce the attachment of junctional epithelium to the tooth; embedded in gel-like extracellular matrix.

  • Dentogingival Unit: Composed of junctional epithelium and supragingival fibers, essential for gingival tissue support.

Functions of Supragingival Fiber Bundles

  • Stabilization: Protect gingiva and tooth alignment during mastication.

  • Connective Functions: Link gingiva to cementum and alveolar bone.

Anatomy of Periodontal Ligament Fibers

  • Structure: Surrounds tooth roots; connects root cementum to the socket wall.

  • Thickness: Varies (0.05 to 0.25 mm), depending on age and tooth function.

  • Cellular Composition: Includes fibroblasts, cementoblasts, osteoblasts, and others.

Principal Fiber Groups of Periodontal Ligament

  • Types:

    • Alveolar crest fibers

    • Horizontal fibers

    • Oblique fibers

    • Apical fibers

    • Interradicular fibers

Sharpey’s Fibers

  • Definition: Calcified ends of periodontal ligaments embedded in cementum and alveolar bone; crucial for attachment.

Microscopic Anatomy of Cementum

  • Definition: Mineralized tissue covering tooth roots; vital for tooth attachment and repair.

  • Composition:

    • Involves collagen fibers and hydroxyapatite crystals.

    • Avascular structure lacking blood vessels and nerves.

Cementum Types

  • Intermediate Cementum: Found at the cementoenamel junction (CEJ).

  • Acellular (Primary) Cementum: Mainly comprised of Sharpey fibers; lacks living cells.

  • Cellular (Secondary) Cementum: Contains cementocytes and fibroblasts, located at the apical and interradicular root regions.

Relationships at the Cementum-Enamel Junction (CEJ)

  • Arrangements: Enamel can:

    • Overlap cementum

    • Meet cementum

    • Present a gap

  • Abbreviation: This is commonly noted as OMG (Overlap, Meet, Gap).

Microscopic Anatomy of Alveolar Bone

  • Definition: Part of the maxilla and mandible forming the tooth socket.

  • Structure:

    1. Alveolar bone proper

    2. Trabecular bone

    3. Cortical (compact) bone

Function of Alveolar Bone

  • Protection: Safeguards tooth roots against mechanical forces.

  • Adaptation: Responds to mechanical stimuli and inflammation.

Key Cells in Alveolar Bone

  • Osteoblasts: Bone-building cells initiating mineralization. (Hint: “b = build”)

  • Osteoclasts: Bone-resorbing cells that remove mineralized material (Hint: “c = consume”).