Orthodontics Lecture Series: Growth and Development

Introduction

• Speaker: Ryan, an orthodontics resident
• Focus on high-yield exam content
• Overview of clinical applications and general knowledge

Growth vs. Development

• Growth:

  • Increase in size or number
  • Hypertrophy: increase in size of cells
  • Hyperplasia: increase in number of cells
  • Quantitative factors: height, weight, length, width

• Development:

  • Increase in complexity or specialization of functions
  • Qualitative factors: day-to-day function, behavior

Laws of Growth and Development

1. Pattern: Predictable changes in how the body grows over time
2. Timing: General ages expected for growth
3. Variability: Individual differences in growth

Cephalocaudal Growth Gradient

• Body parts near the head grow faster initially, while those further away grow later.
• Example:
  • At 2 months in utero, head is 50% of total length; by adulthood, it's 12%.

Kamen's Growth Curves

• Axes:

  • X-axis: age (years)
  • Y-axis: tissue size

• Curves:

  • Lymphoid, Neural, Maxilla, Mandible, General Body, Genital Tissues
  • Neural tissues grow rapidly post-birth, reaching near adult size by ages 6-7.
  • Lymphoid tissues grow rapidly until age 10, then shrink during puberty.
  • Genital tissues grow significantly during the pubertal growth spurt.

Distance and Velocity Growth Curves

• Distance Curve: Tracks accumulated height over time (never decreases).
• Velocity Curve: Shows rate of growth (slope of distance curve).
  • Girls have earlier growth spurts (around age 12) than boys (around age 14).

Assessing Growth and Maturity

• Chronological Age: Common but not always a good indicator of maturity.
• Dental Age: Based on dental development, but less reliable.
• Skeletal Age: Measured by:
  1. CBM Staging: Cervical vertebral maturation from cephalometric x-rays.
  2. Hand-Wrist Method: X-ray of hand/wrist bones.
• Biologic Age: Based on markers like menarche and secondary sex characteristics (best indicator).

Mechanisms of Growth

• Growth Sites: Areas where growth occurs.
• Growth Centers: Sites that can grow independently.

Modes of Growth

1. Endochondral Ossification:

   • Growth from within (increased length).
   • Involves cartilage model replaced by bone.
   • Examples: Epiphyseal plates, cranial base synchondroses.

2. Intramembranous Ossification:

   • Growth from outside (increased thickness).
   • Bone develops directly from connective tissue without cartilage.
   • Example: Cranial vault, maxilla, mandible.

Theories of Craniofacial Growth Control

1. Suture Theory: Genetic control with sutures as growth centers (debunked).
2. Cartilage Theory: Epigenetic control with cartilage determining growth.
3. Functional Matrix Theory: Environmental control where soft tissue growth drives bone and cartilage change.

Regions of Craniofacial Growth

1. Cranial Vault: Grows wider to accommodate the brain.
2. Cranial Base: Growth through endochondral ossification at synchondroses.
3. Maxilla: Grows through intramembranous ossification at sutures and surfaces.
4. Mandible: Mix of intramembranous and endochondral growth mechanisms.

Summary of Growth Patterns

• Width grows first (10-12 years), followed by anteroposterior (14-16 years), and vertical growth (18-20 years or later).

Conclusion

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