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Microscopic Anatomy of the Periodontium

• This chapter focuses on the microscopic structures of the periodontium.
• The foundational aspects of histology, tissue, cells, and extracellular matrix are critical for understanding the complex structures of the periodontium.
• The periodontium is composed of multiple tissues: epithelial, connective, nerve, and muscle, crucial in its overall function.

Microscopic Anatomy of Tissue

• Histology: The study of microscopic features of tissues.
• Tissue: A group of interconnected cells performing similar functions.
• Tissues and organs: Composed of various cell types and extracellular elements.

Cells

• Cells are the smallest structural units capable of independent functioning.
• Cells group together to form tissues.
• There are four basic tissue types: epithelial, connective, nerve, and muscle.

Extracellular Matrix

• A mesh-like network surrounding cells.
• Physically supports cells within tissue.
• Provides a biomechanical framework for cell migration and interaction.
• Primarily composed of ground substance and fibrous proteins.
• Sparse in epithelial tissue (primarily basal lamina).
• Plentiful in connective tissue.

Microscopic Anatomy of Epithelial Tissue

• Forms the outer surface of the body and lines body cavities (mouth, stomach, and intestines).
• Skin and oral mucosa are composed of stratified squamous epithelium (layers of flat cells).
• Epithelial cells are tightly packed and bound together.
• Basal lamina is a thin mat of extracellular matrix secreted by epithelial cells supporting overlying epithelium.

Keratinization

• A process by which surface epithelial cells become stronger and waterproof.
• Keratinized epithelial cells lack nuclei, forming a tough, resistant layer (e.g., skin).
• Nonkeratinized epithelial cells have nuclei and act as a protective cushion.

Blood Supply of Epithelial Cells

• Epithelial cells are avascular (lack blood vessels).
• They receive oxygen and nutrients from blood vessels in underlying connective tissue via diffusion.

Microscopic Anatomy of Connective Tissue

• Fills spaces between tissues and organs in the body.
• Supports or binds other tissues.
• Composed of sparse cells (fibroblasts, phagocytes, lymphocytes) and abundant extracellular substance.
• Dental connective tissues include cementum, dentin, alveolar bone, and pulp.
• Enamel is the exception, classified as epithelial tissue.

Epithelial-Connective Tissue Interface

• The site where epithelial and connective tissues meet.
• Basal lamina is not visible under a light microscope.
• Aids in the attachment of epithelial cells to adjacent structures.
• A basement membrane is visible with a light microscope beneath the epithelium.
• A combination of basal lamina and reticular lamina.
• The most common pattern is tight interdigitation, where tissues interlock like clasped fingers.
• Also composed of epithelial ridges or rete pegs.
• Finger-like extensions of connective tissue projecting into the epithelium.

Morphologic Patterns of the Epithelial-Connective Tissue Interface (cont.)

• Seen in healthy sulcular epithelium and healthy junctional epithelium.
• A smooth non-interdigitizing interface without epithelial or connective tissue papillae.

Function of the Epithelial-Connective Tissue Interface

• Enhances adhesion of epithelium to connective tissue by increasing the surface area.
• Allows skin to resist mechanical forces.
• Provides a large area to receive nourishment from underlying connective tissue.

Epithelial Cell Junctions

• Cellular structures that mechanically 'lock' a cell and its cytoskeleton to its neighbor or basal lamina, forming a structurally strong unit.
• Tissues like the epithelium of the skin have the most abundant number of cell junctions.
• They can withstand severe mechanical stresses.

Desmosomes and Hemidesmosomes

• Create cell-to-cell or cell-to-basal lamina connections.
• Important junctions found in gingival epithelium.

Microscopic Anatomy of Gingival Epithelium

• Specialized stratified squamous epithelium enabling optimal function in a wet oral cavity.
• Three anatomical areas: oral epithelium, sulcular epithelium, and junctional epithelium.

Oral Epithelium

• Covers the outer surface of free and attached gingiva, extending from the crest of the gingival margin to the mucogingival junction.
• Keratinized stratified squamous epithelium.
• Divided into cell layers (e.g., stratum basale, stratum spinosum, stratum corneum).

Cell Layers of the Oral Epithelium

• Includes basal cell layer (stratum basale), prickle cell layer (stratum spinosum), granular cell layer (stratum granulosum), and keratinized cell layer (stratum corneum).

Sulcular Epithelium

• Epithelial lining of the gingival sulcus, continuous with oral epithelium.
• Extends from the crest of the gingival margin to the coronal edge of junctional epithelium.
• Thin, non-keratinized with three distinct layers: basal cell layer, prickle cell layer, and superficial cell layer.
• Permits gingival crevicular fluid flow from gingival connective tissue to the sulcus.

Sulcular Epithelium (cont.)

• Permeable, allowing gingival crevicular fluid to flow into the gingival sulcus.
• The flow increases in cases of disease.
• Joins connective tissue at a smooth interface without epithelial ridges. No interdigitation.

Junctional Epithelium

• Forms the base of the sulcus and joins gingiva to tooth.
• Attaches to the tooth slightly coronal to the cementoenamel junction (CEJ).
• Thin, nonkeratinized, semipermeable.
• The easiest entry point for bacteria into connective tissue.
• Contains only basal and prickle cell layers.
• Approximately 0.71 to 1.35 mm in length and tapers from 15 to 30 cells thick to 4 to 5 cells thick in the apical zone.
• Exhibits a smooth, flush interface with connective tissue in healthy cases.

Functions of Junctional Epithelium

• Attachment.
• Barrier.
• Host defense.

Attachment of the Cells of the Junctional Epithelium

• Components include closely packed epithelial cells, desmosomes, hemidesmosomes, and sparse extracellular matrix with internal and external basal lamina.

Attachment of Junctional Epithelium

• Attaches to the tooth surface through hemidesmosomes.
• Interacts with underlying connective tissue through hemidesmosomes and external basal lamina.

Microscopic Anatomy of Gingival Connective Tissue of the Free and Attached Gingiva

• Function: Provides support to gingiva, attaches gingiva to the cementum of the tooth root and the alveolar bone.
• Also known as lamina propria.
• Abundant extracellular matrix with few cells (around 5%).

Cells of the Gingival Connective Tissue

• Three cell types: fibroblasts (secrete collagen), mast cells, and immune cells (macrophages, neutrophils, lymphocytes).
• Fibers of connective tissue are produced by fibroblasts.

Extracellular Matrix of the Gingival Connective Tissue

• Collagen fibers, fibroblasts, vessels, and nerves are embedded in the extracellular matrix.
• 55% to 65% of the matrix comprises protein fibers.
• 30% to 35% of the matrix is gel-like material.

The Supragingival Fiber Bundles of the Gingival Connective Tissue

• Network of rope-like collagen fiber bundles located coronally to the crest of the alveolar bone.
• Support gingival tissue.

Features of the Supragingival Fiber Bundles

• Embedded in a gel-like extracellular matrix.
• Strengthens attachment of junctional epithelium to the tooth.
• Provides structural support to gingival tissue.

Functions of the Supragingival Fiber Bundles

• Braces the gingiva against the teeth and reinforces junctional epithelium attachment.
• Provides rigidity to withstand mastication forces.
• Connects gingiva to the cementum and alveolar bone.
• Stabilizes adjacent teeth.

Classification of Supragingival Fiber Groups

• Categories include: Circular (C), Alveologingival (AG), Dentogingival (DG), Periosteogingival (PG), Intergingival (IG), Intercircular (IC), Interpapillary (IP), Transgingival (TG), and Transeptal (TS).

The Periodontal Ligament Fibers of the Gingival Connective Tissue

• Thin sheet of fibrous connective tissue surrounding the roots of teeth.
• Connects root cementum to the socket wall.
• Vary in thickness (0.05 to 0.25 mm).
• Composed of connective tissue fibers, cells, and extracellular matrix.

Functions of the Periodontal Ligament Fibers

• Supportive: anchors the tooth to the socket and separates it from the socket wall.
• Sensory: transmits tactile pressure and pain sensations.
• Nutritive: blood vessels nourish the cementum and bone.
• Formative: responsible for collagen formation (fibroblasts), cementum formation (cementoblasts), and bone formation (osteoblasts).
• Resorptive: resorption of bone or cementum in response to pressure.

Principal Fiber Groups of the Periodontal Ligament

• Include: Alveolar crest fibers, Horizontal fibers, Oblique fibers, Apical fibers, and interradicular fibers.

Sharpey's Fibers of the Periodontal Ligament

• Calcified terminal ends of periodontal ligament fibers embedded within cementum and alveolar bone.
• Attachment occurs during cementum and bone formation.

Microscopic Anatomy of Cementum

• Mineralized tissue covering tooth roots.
• Composed mainly of hydroxyapatite (calcium and phosphate).
• Attaches the tooth to the bone via periodontal ligament collagen fibers.
• Maintains root integrity, supports tooth maintenance, aids in repair, and possibly influences periodontal ligament regeneration.

Components of Mature Cementum

• Organic portion: Densely packed collagen fibers and groups of proteins.
• Mineralized portion: Made of hydroxyapatite crystals.
• Blood vessels and nerves absent.
• Biological components: Growth factors produced during formation stored in the matrix.

Conservation of Cementum During Periodontal Instrumentation

• Historically, aggressive removal of cementum was necessary to treat bacterial products.
• Research now demonstrates that bacterial products are not located within the cementum, thus highlighting the importance of preserving the cementum for new attachments.

Types of Cementum

• Categories include: Intermediate (found at the CEJ), Acellular (primary), and Cellular (secondary).

Three Possible Arrangements of Enamel at the Cementum

• Possible arrangements of enamel at the cementum include: Overlap the enamel, meet the enamel, or a gap.
• Often abbreviated as OMG.

Microscopic Anatomy of Alveolar Bone

• Part of the maxilla and mandible forming and supporting tooth sockets.
• Anatomical components include: Alveolar bone proper, Trabecular bone, and Cortical (compact) bone.

Microscopic Anatomy of Alveolar Bone (cont.)

• Function: Protects tooth roots, resists mechanical forces and inflammation.
• Characteristics: Major cell types include osteoblasts and osteoclasts. Rigid extracellular matrix due to mineralization. Blood vessels and nerve innervation.