Ch. 2 Microscopic Anatomy of the Periodontium

Tissue is a group of…

interconnected cells that perform a similar function within an organism

Tissues and organs of the body are composed of several different types of ____ and ________ elements outside of the cells

cells, extracellular

Cells:

Smallest structural unit capable of functioning independently

• as a group, they form tissue

Four basic types of tissue:

1. Epithelial

2. Connective

3. Nerve

4. Muscle

Extracellular Matrix:

• Gel-like substance (mesh-like) containing interwoven protein fibers surrounding most cells

• serves as scaffolding for cells as it creates a framework where cells can interact with one another

• Fibers of the matrix are collage (majority), elastin and reticular fibers

Extracellular Matrix in Epithelial Tissue:

• sparse

• thin mat called basal lamina underlies epithelium

Extracellular Matrix in Connective Tissue:

more plentiful

Microscopic Anatomy of Epithelial Tissue:

• epithelial tissue is the body’s skin or epidermis and lines body cavities (mouth, stomach) mucosa

• closely packed epithelial cells are bound into sheets

• the only part of extracellular tissue that is part of epithelial tissue is the thin mat called basal lamina (supports like a scaffolding)

Keratinized Epithelial Cells:

• process by which epithelial cells on a surface become stronger and waterproof

• keratinized epithelial cells have no nuclei

• mostly heavily keratinized body parts-hands, feet

Non Keratinized Epithelial Cells:

• have nuclei

• softer and more flexible

• found in mucosa: lining of cheeks

  • allows. flexibility to speak and chew

Blood Supply of Epithelial Cells:

• epithelial cells are avascular

• they contain no blood vessels

• receive O2 and nourishment from vessels in underlying connective tissue

  • called diffusion

Connective tissue fills _____ between tissues and organs in the body and ______ or binds other tissue

space, supports

Connective tissue cells are ______ ______ in extracellular matrix

sparsely distributed

Is extracellular matrix a major component of connective tissue?

Yes

Connective tissue is composed of:

• Fibroblasts that form extracellular matrix

• Macrophages that devour invading microorganisms

• Neutrophils that devour invading microorganisms

• Lymphocytes as part of the immune system

Examples of Dental Connective Tissue:

• cementum

• dentin

• alveolar bone

• pulp

The interface is where epithelial tissue and connective tissue meet and can be…

wavy or smooth

• if it is a wavy boundary, it will have deep extensions of epithelial ridges of epithelium that reach down into connective tissue

• epithelial ridges are also called rete pegs

Summary of Epithelial Tissues:

• many, many cells; composed primarily of cells

• very little extracellular matrix

• no blood supply

Summary of Connective Tissue:

• few cells

• comprised mostly of extracellular matrix

• rich blood supply

Wavy Boundaries:

• enhances adhesion of epithelium to connective tissue by increasing surface area

  • allows skin to resist mechanical forces

• provides larger area to receive nourishment from underlying connective tissue

Epithelial Cell Junctions:

• cellular structures that mechanically attach a cell’s cytoskeleton to its neighbor or the basal lamina

• binding is needed to form a structurally strong unit

• the more the mechanical stresses, the more the abundant cell junctions

Cell Junction: Desmosome

connects two neighboring epithelial cell cytoskeletons

• cell-to-cell connection

• found in gingival epithelium

Cell Junctions: Hemidesmosome

connects epithelial cells to the basal lamina

• cell-to-basal lamina connection

• also found in gingival epithelium

Microscopic Anatomy of Gingival Epithelium:

stratified squamous epithelium in the oral cavity functions well in a wet environemnt

Three Anatomical Areas of Gingival Epithelium:

• Oral Epithelium (OE)

• Sulcular Epithelium (SE)

• Junctional Epithelium (JE)

Oral Epithelium:

• covers outer surface of free gingiva and attached gingiva from the crest of the gingival margin to the mucogingival junction

• may be keratinized or parakeratinized (partially keratinized)

• joins connective tissue in a wavy interface with epithelial ridges

Four Layers of Stratified Squamous Epithelium:

• Cube-shaped cells in the basal layer

• Spine-like cells in the prickle cell layer

• Flattened cells in the granular cell layer

• Flattened cells with extensive intracellular keratin in the keratinized cell layer (Stratum Corneum)

Microscopic Anatomy of Sulcular Epithelium:

• the epithelial lining of the gingival sulcus is thin and nonkeratinized

• continuous with oral epithelium extending from crest of gingival margin to coronal edge of junctional epithelium

• permeable, allowing fluid to flow from gingival connective tissue into sulcus-gingival crevicular fluid

The Cellular Layers of the Sulcular Epithelium:

• Basal cell layer

• Prickle cell layer

• Superficial cell layer

Microscopic Anatomy of Junctional Epithelium:

• forms the base of the sulcus and joins gingiva to the tooth

• in health, JE attaches to the tooth slightly coronal to the cementoenamel junction

• thin and nonkeratinized, easily penetrable

• easiest entry point for bacteria to invade into connective tissue

• comprised of closely packed epithelial cells

• has a sparse extracellular matrix with a thin basal lamina between JE and the tooth surface and JE and gingival connective tissue

Two Cell Layers of Junctional Epithelium:

• basal cell layer

• prickle cell layer

15 to 30 cells thick at coronal zone and tapers to 4 to 5 cells thick at the apical zone

Cells next the tooth form __________that attach the internal basal lamina with the tooth surface

hemidesmosomes

Cells next to gingiva that form ____________ that attach the external basal lamina with gingival connective tissue

hemidesmosomes

The interface tissue of the junctional epithelium is ____ with connective tissue

smooth

Junctional Epithelium’s Importance to Teeth:

• when teeth erupt through epithelium (protective coating covering body), they create an opening where bacteria can enter the body

• the body’s attempt to “seal” the opening created during eruption results in junctional epithelium

• JE provides an attachment between gingiva and tooth sealing the base of the periodontal pocket

Microscopic Anatomy of Gingival Connective Tissue:

• also known as lamina propria, gingival connective tissue provides solidity and attaches gingiva to root cementum and alveolar bone

• is the opposite of gingival epithelium in that it has an abundance of extracellular matrix and few cells

• extracellular matrix is produced by fibroblasts

• protein fibers, including collagen fibers, account for 55% to 65% of gingival connective tissue: gel-like material 30-35%

• collagen forms the rigid “cuff” around the tooth

• transportation of water, nutrients, oxygen, and metabolites to the gingiva occurs within the matrix

Three Types of Cells in Gingival Connective Tissues:

• fibroblasts

• mast cells

• immune cells-macrophages, neutrophils, and lymphocytes

Supragingival Fiber Bundles:

• a network of rope-like collagen fiber bundles located coronal to the crest of alveolar bone

• strengthen attachment of JE to tooth by bracing the gingival margin against the tooth

• JE and gingival fibers are known collectively as dentogingival unit

Supragingival Fibers Function to:

• reinforce attachment of JE to tooth

• provide rigidity to free gingiva so it can withstand chewing forces

• connect free gingiva with root cementum and alveolar bone

• connect adjacent teeth to one another

9 different fibers bundles named after orientation and insertion:

• alveologingival

• circular

• dentogingival

• periosteo gingival

• intergingival

• intercurricular

• interpapillary

• transgingival

• transseptal

Periodontal Ligament Fibers:

• rope-like collagen fibers that stretch across space between cementum and alveolar bone of tooth socket

• have a rich supply of nerves and blood vessels

• main function is to provide support and sensing of pain and tactile pressure

• embedded ends are known as Sharpey fibers

5 Principal Periodontal Ligament Fibers:

• alveolar crest

• horizontal

• oblique

• apical

• interradicular

Microscopic Anatomy of Cementum:

• mineralized tissue covering tooth roots

• periodontal ligament fibers embed in cementum to attach tooth to bone

• involved in tooth repair and generation

• seals open dentinal tubules

• continues to grow in thickness as we age, to compensate for occlusal/incisal attrition

Three Components of Mature Cementum:

• Organic: densely packed collagen fibers oriented parallel to long axis of tooth

  • groups of proteins form cementum proteins that may regulate formative mineralization

• Mineralized: hydroxyapatite crystals

• Biologic: growth factor molecules are produced during formation then stored in matrix to assist with periodontal ligament regeneration

Cementum Conservation when Instrumenting:

• instrumentation can lead to exposure of dentin, causing hypersensitivity

• cementum removal is not necessary to eliminate bacteria

• preservation of cementum is important because of its source for growth factors

Three Types of Cementum:

• Intermediate-located at CEJ

• Acellular-composed mainly of Sharpey Fibers, contains no living cells

• Cellular-contains cementocytes and fibroblasts

  • present at apical and interradicular parts of root

Three Arrangements of Cementum to Enamel (OMG):

• cementum overlaps enamel for a short distance

• cementum meets enamel

• cementum leaves a gap between itself and enamel

Functions of Alveolar Bone:

• alveolar bone protects roots of teeth by forming bony sockets that provide support

• constantly undergoes periods of bone remodeling when teeth are subject to mechanical forces

• comprised of mineralized connective tissue formed by osteoblasts

• least stable part of periodontium because of constant osteoclastic/osteoblastic action

Two Major Cell Types:

• osteoblastss which produce the bone matrix of collagen fibers and other protein fibers

• osteoclasts which are cells that remove mineral material and organic matrix of bone

Characteristics of the Alveolar Bone:

• extracellular matrix contains-collagen fibers and gel-like substances-major component

• bone matrix is rigid because of mineral deposition of calcium and phosphate-subsequently transformed into hydroxyapatite

• alveolar bone contains-blood vessels and nerve innervation