2 Microscopic Anatomy of the Periodontium

Microscopic Anatomy of the Periodontium

Chapter Overview

  • Authors: Jill S. Gehrig, Daniel E. Shin

  • Source: Foundations of Periodontics for the Dental Hygienist, Sixth Edition

  • Publisher: Jones & Bartlett Learning

  • Focus: Microscopic anatomy relating to periodontal support structures and tissues.

Microscopic Anatomy of Tissue

  • Histology: The study of microscopic features of tissues, essential for understanding the cellular composition and organization of tissues within the body.

  • Tissue: A group of interconnected cells that perform similar functions; tissues work together to form organs.

Cells

  • Definition: The smallest structural unit capable of functioning independently.

  • Functionality: Cells group together to form various types of tissues.

  • Four Basic Types of Tissue:

    • Epithelial

    • Connective

    • Nerve

    • Muscle

Extracellular Matrix

  • Structure: A mesh-like network surrounding cells that supports and influences their behavior within the tissue.

  • Functions:

    • Physically supports cells

    • Provides a biomechanical framework for cell migration and interaction

  • Composition: Mainly consists of ground substance and fibrous proteins; sparse in epithelial tissues and abundant in connective tissues.

Microscopic Anatomy of Epithelial Tissue

  • General Characteristics: Epithelial tissues form the outer surface of the body and line body cavities.

  • Specifics: The skin and oral mucosa consist of stratified squamous epithelium.

Composition of Epithelial Tissue

  • Structure: Characterized by plentiful cells that are closely packed and bound together.

  • Basal Lamina: A thin layer of extracellular matrix secreted by epithelial cells that supports the overlying epithelium.

Keratinization

  • Definition: The process by which surface epithelial cells become more robust and waterproof.

    • Keratinized Epithelial Cells: Lacking nuclei, forming a tough, resistant layer on skin.

    • Nonkeratinized Epithelial Cells: Contain nuclei and serve as cushioning layers.

Blood Supply of Epithelial Cells

  • Characteristics: Epithelial cells are avascular, meaning they lack blood vessels.

  • Nourishment: Obtain oxygen and nutrients by diffusion from underlying connective tissue vessels.

Microscopic Anatomy of Connective Tissue

  • Functionality: Fills spaces between tissues and organs, providing support and binding other tissues together.

  • Histological Composition: Contains sparse cells, such as fibroblasts, phagocytes, and lymphocytes, along with abundant extracellular substance.

  • Includes Structures: Cementum, dentin, alveolar bone, and pulp, while enamel is categorized as epithelial tissue.

Epithelial-Connective Tissue Interface

  • Definition: The site where epithelial and connective tissues meet, fundamental for tissue adherence.

    • Basal Lamina: Not visible under light microscopy, aids in attaching epithelial cells to adjacent structures.

    • Basement Membrane: A thin layer visible under light microscopy beneath the epithelium, a combination of basal lamina and reticular lamina.

Morphologic Patterns of the Epithelial-Connective Tissue Interface

  • Tight Interdigitation Pattern: Most common; tissues interdigitate like clasped fingers, enhancing adhesion.

    • Epithelial Ridges or Rete Pegs: Extensions of epithelial tissue into connective tissue.

    • Connective Tissue Papillae: Finger-like extensions of connective tissue into the epithelium, correlated with healthy gingival architecture (gingival stippling).

Smooth Non-Interdigitizing Interface

  • Represents areas without epithelial ridges or connective tissue papillae, observed in healthy sulcular and junctional epithelium.

Functions of the Epithelial-Connective Tissue Interface

  • Enhancement of Adhesion: Increases surface area for better attachment of epithelium to connective tissue.

  • Resilience: Contributes to the ability of skin/gingiva to resist mechanical forces while providing nourishment from underlying connective tissue.

Epithelial Cell Junctions

  • Definition: Structures that mechanically connect epithelial cells and their cytoskeletons to neighboring cells or the basal lamina.

  • Importance: Form structurally strong units essential for maintaining integrity in high-stress tissues like skin epithelium.

Types of Epithelial Cell Junctions

Desmosomes

  • Function: Create cell-to-cell connections, crucial in gingival epithelium for structural support.

Hemidesmosomes

  • Function: Form cell-to-basal lamina connections; also crucial in gingival epithelium.

Microscopic Anatomy of Gingival Epithelium

  • Characteristics: Specialized stratified squamous epithelium adapted for a wet oral environment.

  • Anatomical Areas:

    • Oral Epithelium

    • Sulcular Epithelium

    • Junctional Epithelium

Oral Epithelium

  • Location: Covers the outer surface of free and attached gingiva from the crest of the gingival margin to the mucogingival junction.

  • Characteristics: Covered by keratin, divided into multiple cell layers.

Cell Layers of the Oral Epithelium

  • Basal Cell Layer: Stratum basale.

  • Prickle Cell Layer: Stratum spinosum.

  • Granular Cell Layer: Stratum granulosum.

  • Keratinized Cell Layer: Stratum corneum.

Sulcular Epithelium

  • Description: Thin, nonkeratinized epithelial lining of the gingival sulcus, extending from the gingival margin crest to the junctional epithelium's coronal edge.

  • Layers:

    • Basal Cell Layer

    • Prickle Cell Layer

    • Superficial Cell Layer

  • Permeability: Allows flow of gingival crevicular fluid from the connective tissue into the sulcus but presents a flush interface without epithelial ridges.

Junctional Epithelium

  • Location: Forms the base of the sulcus, attaching the gingiva to the tooth.

  • Characteristics: Thin, nonkeratinized, semipermeable; attaches slightly coronal to the cementoenamel junction (CEJ) in health.

  • Structure: Composed of only basal and prickle cell layers.

  • Dimensions: Ranges from 0.71 to 1.35 mm in length, composed of 15 to 30 cells thick at the coronal zone, tapering to 4 to 5 cells thick at the apical zone.

  • Functionality: Represents the easiest entry point for bacteria into connective tissue.

Functions of the Junctional Epithelium

  • Attachment: Secures gingiva to tooth surface.

  • Barrier: Acts as a defense against microbial invasion.

  • Host Defense: Plays a role in immune response.

Attachment Structure of Junctional Epithelium

  • Components:

    • Close-packed epithelial cells

    • Hemidesmosomes and desmosomes

    • Sparse extracellular matrix containing internal and external basal laminae.

Microscopic Anatomy of Gingival Connective Tissue

  • Function: Provides structural solidity to gingiva, adhering it to root cementum and alveolar bone.

  • Also Known As: Lamina propria

  • Composition: Characterized by a high abundance of extracellular matrix with relatively few cells, with cells constituting about 5% of the connective tissue.

Cells of Gingival Connective Tissue

  • Types:

    • Fibroblasts

    • Mast Cells

    • Immune Cells (macrophages, neutrophils, lymphocytes)

  • Function: Fibroblasts produce fibers of connective tissue.

Extracellular Matrix of Gingival Connective Tissue

  • Composition: Contains collagen fibers, fibroblasts, blood vessels, and nerves embedded within the matrix.

  • Ratios: 55% to 65% consist of protein fibers, with 30% to 35% as gel-like material.

Supragingival Fiber Bundles of Gingival Connective Tissue

  • Description: A network of collagen fiber bundles situated coronal to the alveolar bone crest.

Features of Supragingival Fiber Bundles

  • Matrix Integration: Embedded in gel-like extracellular matrix.

  • Functionality: Strengthens the junctional epithelium's attachment to the tooth surface.

  • Dentogingival Unit: Combination of junctional epithelium and supragingival fibers providing structural integrity to gingival tissue.

Functions of Supragingival Fiber Bundles

  • Adhesion: Brace gingiva against the tooth providing attachment reinforcement for junctional epithelium.

  • Resistance and Stability: Provide rigidity to withstand forces during mastication and stabilize adjacent teeth.

Classification of Supragingival Fiber Groups

  1. C: Circular

  2. AG: Alveologingival

  3. DG: Dentogingival

  4. PG: Periosteogingival

  5. IG: Intergingival

  6. IC: Intercircular

  7. IP: Interpapillary

  8. TG: Transgingival

  9. TS: Transseptal

Periodontal Ligament Fibers

  • Description: A thin sheet of fibrous connective tissue surrounding the roots of teeth, anchoring them in place. Thickness ranges between 0.05 mm and 0.25 mm, influenced by age and tooth function.

  • Components: Composed of connective tissue fibers, various cells, and extracellular matrix.

Functions of Periodontal Ligament Fibers

  • Anchor: Secures tooth to its socket while allowing separation from the socket wall.

  • Blood Supply and Innervation: Houses nerve endings and blood vessels vital for sensation and health.

  • Formative Functions: Involves cells like fibroblasts and osteoblasts, aiding in tooth and bone remodeling.

Principal Fiber Groups of the Periodontal Ligament

  1. Alveolar crest fibers

  2. Horizontal fibers

  3. Oblique fibers

  4. Apical fibers

  5. Interradicular fibers

Sharpey’s Fibers

  • Definition: Calcified terminal ends of periodontal ligament fibers embedded in the cementum and alveolar bone during the forming processes.

Microscopic Anatomy of Cementum

  • Definition: A mineralized tissue that covers the roots of teeth, providing attachment to bone via periodontal ligament collagen fibers. Prevalent in maintaining root integrity, it aids tooth repair and regeneration.

  • Biological Role: A key component of periodontal tissues potentially influencing the activities of periodontal cells.

Components of Mature Cementum

  • Organic Portion: Densely packed collagen fibers and protein aggregates.

  • Mineralized Portion: Composed primarily of hydroxyapatite crystals.

  • Characteristic: Lacks blood vessels and nerves, but contains biological components including growth factors encapsulated within the matrix.

Conservation of Cementum During Periodontal Instrumentation

  • Historical Perspective: Aggressive removal of cementum previously recommended due to bacterial penetration concerns.

  • Current Research: Suggests that bacterial by-products do not reside in cementum, advocating for its preservation for potential new attachment and growth factors.

Types of Cementum

  1. Intermediate

  2. Acellular (Primary)

  3. Cellular (Secondary)

Enamel-Cementum Arrangement

  • Possible Arrangements:

    1. Overlap the enamel

    2. Meet the enamel

    3. Gap

  • Abbreviation: Often referred to as OMG; all three arrangements may exist concurrently.

Microscopic Anatomy of Alveolar Bone

  • Description: Comprises part of the maxilla and mandible that forms and supports the teeth sockets.

  • Anatomical Components:

    1. Alveolar bone proper

    2. Trabecular bone

    3. Cortical (compact) bone

Alveolar Bone Functionality and Characteristics

  • Functions: Protects tooth roots, responds to mechanical forces and infection/inflammation.

  • Major Cell Types: Osteoblasts (bone formation) and osteoclasts (bone resorption).

  • Extracellular Matrix: Rigid due to mineralization, containing blood vessels and nerve innervation for physiological functions.