Anatomy and Histology of the Periodontium

Gingiva (normal clinical appearance): no muscles, no glands; keratinized

• Color: coral pink but does vary with individuals and races due to cutaneous pigmentation
• Papillary contour: pyramidal shape with one F and one L papilla and the col filling interproximal space to the contact area (col the starting place gingivitis)
• Marginal contour: knife-edged and scalloped
• Texture: stippled (orange-peel texture); blow air to dry out and see where stippling ends to see end of gingiva
• Consistency: firm and resilient (push against it and won’t move); bound to underlying bone
• Sulcus depth: 0-3mm
• Exudate: no exudates (blood, pus, water)

  Anatomic and histological structures

Gingival unit: includes periodontium above alveolar crest of bone

a. Alveolar mucosa: histology- non-keratinized, stratified, squamous epithelium, submucosa with glands, loose connective tissue with collagen and elastin, muscles.  No epithelial ridges, no stratum granulosum (flattened cells below keratin layer)

b. Mucogingival junction: clinical demarcation between alveolar mucosa and attached gingiva

c. Attached gingiva: histology- keratinized, stratified, squamous epithelium with epithelial ridges (basal cell layer, prickle cell layer, granular cell layer (stratum granulosum), keratin layer); no submucosa

• Dense connective tissue: predominantly collagen, bound to periosteum of bone by Sharpey fibers
• Reticular fibers between collagen fibers and are continuous with reticulin in blood vessels

d. Free gingival groove: demarcation between attached and free gingiva; denotes base of gingival sulcus in normal gingiva; not always seen

e. Free gingival margin: area from free gingival groove to epithelial attachment (up and over ® inside)

• Oral surface: stratified, squamous epithelium with epithelial ridges
• Tooth side surface (sulcular epithelium): non-keratinized, stratified, squamous epithelium with no epithelial ridges (basal cell and prickle cell layers)

f. Gingival sulcus: space bounded by tooth surface, sulcular epithelium, and junctional epithelium; 0-3mm depth; space between epithelium and tooth

g. Dento-gingival junction: combination of epithelial and fibrous attachment

• Junctional epithelium (epithelial attachment): attachment of epithelial cells by hemi-desmosomes and sticky substances (basal lamina- 800-1200 A, DAS-acid mucopolysaccharides, hyaluronic acid, chondroitin sulfate A, C, and B), to enamel, enamel and cementum, or cementum depending on stage of passive eruption.  Length ranges from 0.25-1.35mm.
• Fibrous attachment: attachment of collagen fibers (Sharpey’s fibers) into cementum just beneath epithelial attachment; ~ 1mm thick

h. Nerve fibers: myelinated and non-myelinated (for pain) in connective tissue.  Both free and specialized endings for pain, touch pressure, and temperature -> proprioception.  If dentures, rely on TMJ.

i.Mesh of terminal argyophilic fibers (stain silver), some extending into epithelium

ii  Meissner-type corpuscles: pressure sensitive sensory nerve encased in CT

iii.Krause-type corpuscles: temperature receptors

iv. Encapsulated spindles

i. Gingival fibers:

i.  Gingivodental group:

• Group I (A): from cementum to free gingival margin
• Group II (B): from cementum to attached gingiva
• Group III (C): from cementum over alveolar crest to periosteum on buccal and lingual plates

ii.  Circular (ligamentum circularis): encircles tooth in free gingiva

iii. Transeptal fibers: connects cementum of adjacent teeth, runs over interdental septum of alveolar bone.  Separates gingival unit from attachment apparatus.

Transeptal and Group III fibers the major defense against stuff getting into bone and ligament.

2.  Attachment apparatus: periodontium below alveolar crest of bone

Periodontal ligament: Sharpey’s fibers (collagen) connecting cementum to bone (bundle bone).  Few elastic and oxytalan fibers associated with blood vessels and embedded in cementum in cervical third of tooth.  Components divided as follows:

i. Alveolar crest fibers: from cementum just below CEJ apical to alveolar crest of bone

ii.Horizontal fibers: just apical to alveolar crest group, run at right angles to long axis of tooth from cementum horizontally to alveolar bone proper

iii.Oblique fibers: most numerous, from cementum run coronally to alveolar bone proper

iv. Apical fibers: radiate from cementum around apex of root apically to alveolar bone proper, form socket base

v. Interradicular fibers: found only between roots of multi-rooted teeth from cementum to alveolar bone proper

vi. Intermediate plexus: fibers which splice Sharpey’s fibers from bone and cementum

vii. Epithelial Rests of Malassez: cluster and individual epithelial cells close to cementum which are remnants of Hertwig’s epithelial root sheath; potential source of periodontal cysts.

viii. Nerve fibers: myelinated and non-myelinated; abundant supply of sensory free nerve endings capable of transmitting tactile pressure and pain sensation by trigeminal pathway and elongated spindle-like nerve fiber for proprioceptive impulses

Cementum: 45-50% inorganic; 50-55% organic (enamel is 97% inorganic; dentin 70% inorganic)

i.  Acellular cementum: no cementocytes; covers dentin (older) in coronal ½ to 2/3 of root, 16-60 mm thick

ii. Cellular cementum: cementocytes; covers dentin in apical ½ to 1/3 of root; also may cover acellular cementum areas in repair areas, 15-200 mm thick

iii. Precementum (cementoid): meshwork of irregularly arranged collagen in surface of cementum where formation starts

iv. Cemento-enamel junction (CEJ): 60-65% of time cementum overlaps enamel; 30% meet end-to-end; 5-10% space between

v. Cementum slower healing than bone or PDL.  If expose dentinotubules ® root sensitivity.

Alveolar bone: 65% inorganic, 35% organic

i. Alveolar bone proper (cribriform plate): lamina dura on x-ray; bundle bone receive Sharpey fibers from PDL

ii. Supporting bone: cancellous, trabecular (vascularized) and F and L plates of compact bone

Blood supply to periodontium

i. Alveolar blood vessels (inferior and superior)

A) Interalveolar: actually runs through bone then exits, main supply to alveolar bone and PDL

B) Supraperiosteal: just outside bone, to gingiva and alveolar bone

C) Dental (pulpal): to pulp and periapical area

D) Terminal vessels (supracrestal): anastomose of A and B above beneath the sulcular epithelium

E) PDL gets blood from: most from branches of interalveolar blood vessels from alveolar bone marrow spaces, supraperiosteal vessels when interalveolar vessels not present, pulpal (apical) vessels, supracrestal gingival vessels

ii. Lymphatic drainage: accompany blood vessels to regional lymph nodes (esp. submaxillary group)

Junctional Epithelium

The junctional epithelium (JE) is a critical component of the periodontal tissue, playing a vital role in the attachment of the gingiva to the tooth surface. Understanding its structure, function, and development is essential for comprehending periodontal health and disease.

Structure of the Junctional Epithelium

1. Composition:

   • The junctional epithelium consists of a collar-like band of stratified squamous non-keratinized epithelium.
   • This type of epithelium is designed to provide a barrier while allowing for some flexibility and permeability.

2. Layer Thickness:

   • In early life, the junctional epithelium is approximately 3-4 layers thick.
   • As a person ages, the number of epithelial layers can increase significantly, reaching 10 to 20 layers in older individuals.
   • This increase in thickness may be a response to various factors, including mechanical stress and inflammation.

3. Length:

   • The length of the junctional epithelium typically ranges from 0.25 mm to 1.35 mm.
   • This length can vary based on individual anatomy and periodontal health.

Development of the Junctional Epithelium

• The junctional epithelium is formed by the confluence of the oral epithelium and the reduced enamel epithelium during the process of tooth eruption.
• This fusion is crucial for establishing the attachment of the gingiva to the tooth surface, creating a seal that helps protect the underlying periodontal tissues from microbial invasion.

Function of the Junctional Epithelium

• Barrier Function: The junctional epithelium serves as a barrier between the oral cavity and the underlying periodontal tissues, helping to prevent the entry of pathogens.
• Attachment: It provides a strong attachment to the tooth surface, which is essential for maintaining periodontal health.
• Regenerative Capacity: The junctional epithelium has a high turnover rate, allowing it to regenerate quickly in response to injury or inflammation.

Clinical Relevance

• Periodontal Disease: Changes in the structure and function of the junctional epithelium can be indicative of periodontal disease. For example, inflammation can lead to increased permeability and loss of attachment.
• Healing and Repair: Understanding the properties of the junctional epithelium is important for developing effective treatments for periodontal disease and for managing healing after periodontal surgery.

Components of Gingival Crevicular Fluid (GCF) and Matrix Metalloproteinases (MMPs)

Gingival crevicular fluid (GCF) is a serum-like fluid found in the gingival sulcus that plays a significant role in periodontal health and disease. Understanding its composition, particularly glucose and protein content, as well as the role of matrix metalloproteinases (MMPs) in tissue remodeling, is essential for dental professionals.

Composition of Gingival Crevicular Fluid (GCF)

1. Glucose and Hexosamines:

   • GCF contains compounds such as glucose, hexosamines, and hexuronic acid.
   • Glucose Levels:
     • Blood glucose levels do not correlate with GCF glucose levels; in fact, glucose concentration in GCF is three to four times greater than that in serum.
     • This elevated glucose level is interpreted as a result of the metabolic activity of adjacent tissues and the influence of local microbial flora.

2. Protein Content:

   • The total protein content of GCF is significantly less than that of serum.
   • This difference in protein concentration reflects the unique environment of the gingival sulcus and the specific functions of GCF in periodontal health.

Matrix Metalloproteinases (MMPs)

1. Definition and Function:

   • MMPs are a family of proteolytic enzymes that degrade extracellular matrix molecules, including collagen, gelatin, and elastin.
   • They are produced by various cell types, including:
     • Neutrophils
     • Macrophages
     • Fibroblasts
     • Epithelial cells
     • Osteoblasts and osteoclasts

2. Classification:

   • MMPs are classified based on their substrate specificity, although it is now recognized that many MMPs can degrade multiple substrates. The classification includes:
     • Collagenases: e.g., MMP-1 and MMP-8 (break down collagen)
     • Gelatinases: Type IV collagenases
     • Stromelysins
     • Matrilysins
     • Membrane-type metalloproteinases
     • Others

3. Activation and Inhibition:

   • MMPs are secreted in an inactive form (latent) and require proteolytic cleavage for activation. This activation is facilitated by proteases such as cathepsin G produced by neutrophils.
   • Inhibitors: MMPs are regulated by proteinase inhibitors, which possess anti-inflammatory properties. Key inhibitors include:
     • Serum Inhibitors:
       • α1-antitrypsin
       • α2-macroglobulin (produced by the liver, inactivates various proteinases)
     • Tissue Inhibitors:
       • Tissue inhibitors of metalloproteinases (TIMPs), with TIMP-1 being particularly important in periodontal disease.
   • Antibiotic Inhibition: MMPs can also be inhibited by tetracycline antibiotics, leading to the development of sub-antimicrobial formulations of doxycycline as a systemic adjunctive treatment for periodontitis, exploiting its anti-MMP properties.

Merkel Cells

1. Location and Function:
   • Merkel cells are located in the deeper layers of the epithelium and are associated with nerve endings.
   • They are connected to adjacent cells by desmosomes and are identified as tactile receptors.
   • These cells play a role in the sensation of touch and pressure, contributing to the sensory functions of the oral mucosa.

Clinical Implications

1. GCF Analysis:

   • The composition of GCF, including glucose and protein levels, can provide insights into the inflammatory status of the periodontal tissues and the presence of periodontal disease.

2. Role of MMPs in Periodontal Disease:

   • MMPs are involved in the remodeling of periodontal tissues during inflammation and disease progression. Understanding their regulation and activity is crucial for developing therapeutic strategies.

3. Therapeutic Applications:

   • The use of sub-antimicrobial doxycycline as an adjunctive treatment for periodontitis highlights the importance of MMP inhibition in managing periodontal disease.

4. Sensory Function:

   • The presence of Merkel cells in the gingival epithelium underscores the importance of sensory feedback in maintaining oral health and function.

Stippling of the Gingiva

• Stippling refers to the textured surface of the gingiva that resembles the skin of an orange. This characteristic is best observed when the gingiva is dried.

• Characteristics:

  • Location:
    • The attached gingiva is typically stippled, while the marginal gingiva is not.
    • The central portion of the interdental gingiva may exhibit stippling, but its marginal borders are usually smooth.
  • Surface Variation:
    • Stippling is generally less prominent on the lingual surfaces compared to the facial surfaces and may be absent in some individuals.
  • Age-Related Changes:
    • Stippling is absent in infancy, begins to appear around 5 years of age, increases until adulthood, and may start to disappear in old age.

Attached Gingiva

• Definition: The attached gingiva is the portion of the gingiva that is firmly bound to the underlying alveolar bone and extends from the free gingival groove to the mucogingival junction, where it meets the alveolar mucosa.

• Characteristics:

  • Structure:
    • The attached gingiva is classified as a mucoperiosteum, tightly bound to the underlying alveolar bone.
  • Width:
    • The width of the attached gingiva is greatest in the incisor region, measuring approximately:
      • 3.5 – 4.5 mm in the maxilla
      • 3.3 – 3.9 mm in the mandible
    • It is narrower in the posterior segments, measuring about:
      • 1.9 mm in the maxillary first premolars
      • 1.8 mm in the mandibular first premolars.
  • Histological Features:
    • The attached gingiva is thick and keratinized (or parakeratinized) and is classified as masticatory mucosa.
    • Masticatory mucosa is characterized by a keratinized epithelium and a thick lamina propria, providing resistance to mechanical forces.

Masticatory vs. Lining Mucosa

• Masticatory Mucosa:

  • Found in areas subject to high compression and friction, such as the gingiva and hard palate.
  • Characterized by keratinized epithelium and a thick lamina propria, making it resistant to masticatory forces.

• Lining Mucosa:

  • Mobile, distensible, and non-keratinized.
  • Found in areas such as the lips, cheeks, alveolus, floor of the mouth, ventral surface of the tongue, and soft palate.

• Specialized Mucosa:

  • Found on the dorsum of the tongue, adapted for specific functions such as taste.

Transforming Growth Factor-Beta (TGF-β)

Transforming Growth Factor-Beta (TGF-β) is a multifunctional cytokine that plays a critical role in various biological processes, including development, tissue repair, immune regulation, and inflammation. Understanding its functions and mechanisms is essential for appreciating its significance in health and disease.

Overview of TGF-β

1. Half-Life:

   • Active TGF-β has a very short half-life of approximately 2 minutes. This rapid turnover is crucial for its role in dynamic biological processes.

2. Functions:

   • TGF-β is involved in several key physiological and pathological processes:
     • Development: Plays a vital role in embryonic development and organogenesis.
     • Tissue Repair: Promotes wound healing and tissue regeneration by stimulating the proliferation and differentiation of various cell types.
     • Immune Defense: Modulates immune responses, influencing the activity of immune cells.
     • Inflammation: Regulates inflammatory processes, contributing to both pro-inflammatory and anti-inflammatory responses.
     • Tumorigenesis: Involved in cancer progression, where it can have both tumor-suppressive and tumor-promoting effects depending on the context.

3. Cellular Effects:

   • Stimulates:
     • Osteoblasts: Promotes the differentiation and activity of osteoblasts, which are responsible for bone formation.
     • Fibroblasts: Enhances the proliferation and activity of fibroblasts, contributing to extracellular matrix production and tissue repair.
   • Inhibits:
     • Osteoclasts: Suppresses the activity of osteoclasts, which are responsible for bone resorption.
     • Epithelial Cells: Inhibits the proliferation of epithelial cells, affecting tissue homeostasis.
     • Most Immune Cells: Generally inhibits the activation and proliferation of various immune cells, contributing to its immunosuppressive effects.

4. Production and Activation:

   • TGF-β is produced as an inactive propeptide (latent form) and requires activation to become biologically active.
   • Activation Conditions: The activation of TGF-β typically requires acidic conditions, which can occur in various physiological and pathological contexts, such as during inflammation or tissue injury.

Clinical Implications

1. Wound Healing:

   • TGF-β is crucial for effective wound healing and tissue repair, making it a target for therapeutic interventions in regenerative medicine.

2. Bone Health:

   • Its role in stimulating osteoblasts makes TGF-β important in bone health and diseases such as osteoporosis.

3. Cancer:

   • The dual role of TGF-β in tumorigenesis highlights its complexity; it can act as a tumor suppressor in early stages but may promote tumor progression in later stages.

4. Autoimmune Diseases:

   • Due to its immunosuppressive properties, TGF-β is being studied for its potential in treating autoimmune diseases and in transplant medicine to prevent rejection.

Desquamative Gingivitis

• Characteristics: Desquamative gingivitis is characterized by intense erythema, desquamation, and ulceration of both free and attached gingiva.
• Associated Diseases:
  • Lichen Planus
  • Pemphigus
  • Pemphigoid
  • Linear IgA Disease
  • Chronic Ulcerative Stomatitis
  • Epidermolysis Bullosa
  • Systemic Lupus Erythematosus (SLE)
  • Dermatitis Herpetiformis