35 - Eruption & shedding - Marchant 2024

1. Introduction to Tooth Eruption and Shedding

  • Speaker: Jeffrey K. Marchant, Ph.D.

  • Focus: Mechanisms of tooth movement, eruption, shedding, and associated structures

2. Objectives of the Presentation

  • Tooth Movements: Understand the various types of tooth movements

  • Eruption Mechanisms: Grasp the mechanisms driving tooth eruption and influencing factors

  • Tooth Resorption: Describe the mechanisms of tooth resorption

  • Primary Cuticle and Attachment Epithelium: Discuss formation and function

3. Types of Tooth Movements

3.1 Pre-eruptive Movements

  • Occurs up to crown completion (before root formation)

  • Caused by:

    • Permanent tooth growth

    • Jaw growth

  • Linked with alveolar bone remodeling

  • Involves:

    • Body movement

    • Resorption

    • Synthesis

    • Compression & Tension

3.2 Eruptive Movements (Prefunctional)

  • Initiates during root formation

  • Crown formation complete

  • Involves fusion of:

    • Reduced enamel epithelium (REE) and oral epithelium (OE)

  • Tooth emergence and intraoral movement until opposing crown contact

3.3 Functional Movements

  • Associated with root completion

  • Duration: 1-1.5 years for primary teeth, 2-3 years for permanent teeth

  • Final organization of periodontal ligament (PL) fibers occurs

  • Compensatory movements for:

    • Enamel wear

    • Tooth wear/loss

4. Forces Driving Tooth Eruption

4.1 Pulpal Pressure and Growth

  • Growth of pulpal cells creates force

  • Sympathectomy affects vascular dilation and eruption timing

  • Surgical removal shows pulp is not essential for eruption

4.2 Traction by Periodontal Fibers

  • Collagen fibers contract, assisting in upward tooth movement

  • Myofibroblasts in PL aid contraction

  • Lathyrogens disrupt collagen but do not hinder eruption

4.3 Root Elongation

  • Roots drive crown movement toward the oral cavity

  • Seen in various conditions like rootless teeth and dentin dysplasia

4.4 Alveolar Bone Remodeling

  • Bone formation supports erupting tooth; resorption accommodates root

  • Effects of bone growth on exposure are noted

5. Mechanisms of Eruption

  • Pressure Changes:

    • Reduced pressure above tooth

    • Increased pressure below promotes fibroblast proliferation and vascular supply

6. Factors Affecting Eruption

6.1 Local Factors

  • Overcrowding

  • Tooth impaction

  • Ankylosis

6.2 Systemic Factors

  • Osteopetrosis

  • Calcium disruptions (e.g., Rickets)

6.3 Environmental Factors

  • Presence of supernumerary teeth

7. Pathway of Permanent Tooth Eruption

  • Gubernacular Cord:

    • Guides tooth eruption

    • Removal shows independence from this structure

  • Eruption Rates: 1-10 μm/day (intraosseous); 75 μm/day (extraosseous)

8. Tooth Resorption Mechanisms

8.1 Involving Odontoclasts

  • Role of monocyte-macrophage differentiation in resorption

  • Different resorptive cells: odontoclasts, ameloclasts, cementoclasts, osteoclasts

8.2 Primary Cuticle Formation

  • Fusion of reduced enamel epithelium with oral epithelium

8.3 Junctional Epithelium Construction

  • Layers involved include: outer enamel epithelium (OEE), inner enamel epithelium (IEE), oral epithelium (OE)

9. The Role of the Junctional Epithelium

  • Establishes attachment between gingival soft tissue and tooth enamel structure

  • Significant in health and disease states of the periodontium