Microscopic Anatomy of the Periodontium Study Notes

Chapter 2—Microscopic Anatomy of the Periodontium

Section 2—Microscopic Anatomy of the Gingival Epithelium

Topic Overview—Gingival Histology

  • What are the microscopic characteristics of the epithelial tissue of the gingiva?

  • How are the epithelial cells of the gingiva connected?

  • How does the gingiva connect to the tooth?

Gingival Epithelium

  • It is a type of stratified squamous epithelium designed to function well in the wet environment of the oral cavity.

  • Microscopic anatomy is similar to that of the skin.

Gingival Tissue

  • The gingival tissue consists of:

    • A thin protective layer of the epithelial tissue, covering the underlying connective tissue.

Anatomical Areas of the Gingival Epithelium

  1. Oral epithelium—covers the free and attached gingiva

  2. Sulcular epithelium—lines the sulcus

  3. Junctional epithelium—located at the base of the sulcus

Oral Epithelium (OE)

  • Epithelial covering of the outer surface of the free and attached gingiva.

  • Extends from the crest of the gingival margin to the mucogingival junction.

  • The junction between OE and the underlying connective tissue is a wavy boundary in health.

  • The oral epithelium may be keratinized or parakeratinized (partially keratinized).

  • Tall epithelial ridges of the OE extend down into the underlying connective tissue.

  • A dense network of collagen fibers is visible in the connective tissue.

Sulcular Epithelium (SE)

  • The epithelial lining of the gingival sulcus.

  • Consists of a thin, nonkeratinized epithelium, making it less resistant to stresses.

  • The junction of the SE with the connective tissue is smooth in health (no wavy junction).

  • The SE is permeable, allowing fluid to flow from the gingival connective tissue into the sulcus—gingival crevicular fluid.

Junctional Epithelium (JE)

  • The epithelium that forms the base of the sulcus and joins the gingiva to the tooth.

  • Length = 0.71 mm to 1.35 mm.

  • Thickness: 15 to 30 cells thick at the coronal zone, 4 to 5 cells thick at the apical zone.

  • Nonkeratinized epithelium, making these cells less protective compared to the oral epithelium.

Keratinization

  • The epithelial cells of both the sulcular and junctional epithelium are nonkeratinized, hence these areas provide the easiest entry point for bacteria to invade the underlying connective tissue.

  • In health, the JE has a smooth interface with the connective tissue (no wavy junction).

Importance of Epithelium

  • A continuous sheet of epithelium protects the body and covers all its outer surfaces.

  • This epithelial covering creates a barrier to prevent bacteria and viruses from entering the body.

Importance of Junctional Epithelium

  • When a tooth erupts, it penetrates the oral epithelium, creating an opening for microorganisms to enter the body like an open door.

  • The body attempts to seal the opening by attaching the gingival epithelium to the tooth—this connection forms the junctional epithelium.

Junctional Epithelium Anatomy

  • Like epithelial tissues elsewhere, the junctional epithelium has:

    • Cells

    • Extracellular matrix (EM) consisting of two thin mats: internal basal lamina and external basal lamina.

  • Epithelial cells are connected by desmosomes.

Functions of the Junctional Epithelium

  • The JE attaches the gingiva to the enamel and/or cementum of the tooth.

  • Provides a seal at the base of the gingival sulcus or periodontal pocket.

  • Acts as a protective barrier between plaque biofilm and underlying connective tissue of the periodontium.

Attachments at Different Levels

  • Attachment to the Tooth Surface: Epithelial cells attach using:

    • Hemidesmosomes

    • Internal basal lamina

  • Attachment to the Connective Tissue: Epithelial cells attach using:

    • Hemidesmosomes

    • External basal lamina

Recap—Gingival Epithelium

  • The OE covers the outer surface of the gingiva.

  • The SE lines the gingival sulcus, and the JE forms the base of the sulcus and attaches the gingival epithelium to the tooth.

  • In health, the OE has a wavy boundary with connective tissue, whereas SE and JE have smooth boundaries.

  • JE presents plentiful cells, connected by desmosomes, with an extracellular matrix consisting of internal and external basal lamina.

Section 3—Microscopic Anatomy of Gingival Connective Tissue

Topic Overview—Connective Tissue

  • What are the microscopic characteristics of the connective tissue of the gingiva?

  • What are the microscopic characteristics of the periodontal ligament?

Gingival Connective Tissue

  • It provides solidity to the gingiva and attaches gingiva to the cementum of the root and the alveolar bone.

  • Also known as lamina propria.

Extracellular Matrix (ECM)

  • The gingival connective tissue has an abundant extracellular matrix, consisting of:

    • Cells constitute only 5% of the gingival connective tissue.

    • Protein fibers (collagen) make up about 55% to 65% of the gingival connective tissue, forming a dense network that holds connective tissue together.

Comparison: Epithelial vs Connective Tissue of the Gingiva

  • Epithelial Tissues:

    • Many, many cells; composed primarily of cells

    • Very little extracellular matrix

    • No blood supply

    • Contains internal and external basal lamina

  • Connective Tissue:

    • Few cells but comprises mostly of extracellular matrix (strong, ropelike fibers)

    • Rich blood supply

Supragingival Fiber Bundles

  • A network of ropelike collagen fiber bundles in the gingival connective tissue.

Functions of Fiber Bundles

  • Brace the free gingiva firmly against the tooth.

  • Reinforce attachment of the junctional epithelium to the tooth.

  • Provide rigidity to withstand chewing.

  • Unite free gingiva with the cementum of the root and bone.

  • Connect adjacent teeth to one another.

Fiber Groups

  1. Circular Fibers: Encircle the tooth in a ring-like manner, not attached to cementum; connect adjacent teeth.

  2. Alveologingival Fibers: Extend from periosteum of alveolar crest into gingival connective tissue, attaching gingiva to bone.

  3. Dentogingival Fibers: Embedded in cementum near the CEJ; fan out into lingual connective tissue to attach gingiva to teeth.

  4. Periostogingival Fibers: Extend laterally from periosteum of alveolar bone, attaching gingiva to bone.

Additional Fiber Groups

  • Intergingival Fibers (IG): Extend in a mesiodistal direction along the dental arch, linking adjacent teeth into a dental unit.

  • Intercircular Fibers (IC): Encircle several teeth, linking adjacent teeth into a dental unit.

  • Interpapillary Fibers (IP): Located in papillae, connecting oral and vestibular interdental papillae of posterior teeth.

  • Transgingival Fibers (TG): Connect tissues along the direction of the teeth.

  • Transseptal Fibers (TS): Pass from the cementum of one tooth over the crest of alveolar bone to the adjacent tooth, securing alignment of teeth in arch.

Dentogingival Unit

  • The junctional epithelium plus the gingival fibers forms the dentogingival unit, providing structural support to the gingival tissue.

Section 4—Microscopic Anatomy of Root Cementum and Alveolar Bone

Topic Overview—Cementum and Alveolar Bone

  • What are the microscopic characteristics of cementum?

  • What are the microscopic characteristics of alveolar bone?

Microscopic Anatomy of Cementum

  • Defined as the calcified layer of connective tissue that covers the root of the tooth.

  • A thin layer of cementum covers the dentin of the root, and the periodontal ligament holds the tooth in the bony socket of the alveolar bone.

Functions of Cementum

  • Seals and covers open dentinal tubules.

  • Acts to protect the underlying dentin.

  • Attaches periodontal fibers to the tooth.

  • Forms at the apical areas of roots to compensate for the loss of tooth tissue caused by attrition.

Components of Cementum

  • Organic matrix: Composed of densely packed collagen fibers held together with a gel matrix.

  • Mineralized portion: Contains no blood vessels or nerves.

Types of Cementum

  1. Acellular Cementum:

    • Contains no cementocytes within the mineralized tissue.

    • First to be formed, covering the cervical third or half of the root.

    • Not produced during the life of the tooth.

    • Thickness ranges from 30 to 60 µm and consists mostly of Sharpey fibers.

  2. Cellular Cementum:

    • Contains cementocytes within the mineralized tissue.

    • Continues to form after the tooth erupts.

    • Less calcified than acellular cementum, deposited at intervals throughout the life of the tooth.

    • Thickness ranges from 150 to 200 µm.

Cementoenamel Junction (CEJ)

  • The cementum may have one of three relationships with the enamel of the tooth crown:

    • Overlap—60% of cementum overlaps the enamel.

    • Meet—30% of cementum meets the enamel.

    • Gap—10% small gap between the cementum and enamel.

Microscopic Anatomy of the Alveolar Bone

  • Consists of:

    1. Alveolar bone proper

    2. Trabecular bone

    3. Compact bone

Functions of Alveolar Bone

  • Forms the bony sockets of the teeth.

  • Supports and protects the roots of the teeth.

Characteristics of Alveolar Bone

  • Mineralized connective tissue made by osteoblasts, rigid due to calcium salts deposited in the extracellular matrix.

  • Contains blood vessels and nerves; constantly undergoes formation and resorption.

Components of Alveolar Bone

  • Osteoblasts: Bone builders that initiate mineralization.

  • Osteoclasts: Bone consumers that remove mineralized material and the organic matrix.

Recap—Cementum and Alveolar Bone

  • The cementum meets the enamel in one of three possible relationships—overlap, meet, or gap (remember OMG).

  • The alveolar bone is mineralized connective tissue made by osteoblasts, constantly undergoing periods of formation and resorption.