Craniofacial Growth Theories Quiz

Introduction to Growth & Development

• Growth is a general term, implying changes in magnitude, specifically an increase in size.
• Growth, in the context of anatomy, refers to an increase in size.
• Growth can also be defined as the normal change in the amount of living substance.
• Commonly, growth refers to an increase in size and number.
• Growth is a measurable change in any morphological parameter.
• Growth is the process of self-multiplication of living substance.

Development

• Development is a progress towards maturity.
• Development encompasses all naturally occurring, progressive, and unidirectional sequential changes from a single cell to a multi-functional unit, ending with death.
• Development signifies a maturational process characterized by progressive differentiation at the cellular and tissue levels.

Major Themes of Development

• Changing complexity: Complexity increases during development from the sub-cellular to the whole organism. A complex period for developing dentition is when the dentitions transition from each other.
• Shifts from competent to fixation: Differentiated undifferentiated cells become fixed.
• Shifts from dependent to independent: Increasing independence within all organizational levels as development progresses.
• Ubiquity of genetic control modulated by environment: Genetic control during development is constantly altered by environmental interactions.

Growth and Development

• Growth is mostly an anatomical phenomenon that is quantitative in nature.
• Development is physiological and behavioral, often qualitative in nature.
• The two processes work in tandem, with morphogenetic patterns relying on self-multiplication, differentiation, and organization; time acts as the fourth dimension.

Components of Growth

• Craniofacial growth can be divided into growth mechanism, growth pattern, and growth timing.

Growth Mechanism

• At the cellular level, increased cell size (hypertrophy) or cell number (hyperplasia) are potential growth mechanisms.
• Secretion of extracellular material may also contribute to soft tissue and uncalcified cartilage growth.
• Growth mechanisms differ for hard tissues, as they do not mineralize like soft tissues.
• Bone growth, due to its calcified nature, does not rely on proliferation or hypertrophy of cells but on specific growth mechanisms like intramembranous and endochondral ossification.

Bone Growth Mechanisms

• Intramembranous Bone Formation:

  • Undifferentiated cells of connective tissue cluster together.
  • Primary ossification center forms small spicules of bone.
  • Osteoblasts form organic matrix which eventually ossifies.
  • A delicate trabecular meshwork forms before osteoid formation rapidly calcifies.

• Endochondral Bone Formation:

  • Hypertrophy of chondrocytes and matrix calcifies.
  • Cells degenerate.
  • Blood vessels and connective tissues invade the area.
  • Osteoblasts differentiate and produce osteoid tissue.
  • Osteogenic tissues replace degenerating cartilage.
  • Osteoblastic tissue calcifies.

• Bone Development Stages: Details on bone development stages from primary ossification centers & cartilage cavity formation, vascular invasion and spongy bone formation to formation of periosteum, and secondary ossification centers to final ossification of epiphyses with cartilage formation only in epiphyseal and articular cartilages.

Types of Cranial Cartilage

• Primary cartilage, like the spheno-occipital synchondrosis, nasal septal cartilage are insensitive to local factors.
• Secondary cartilage, like the condylar and coronoid cartilages, are influenced by local factors with modulating effects.

Mechanisms of Growth

• Ossification: Apposition at sutures, remodeling of bones, and the growth centers at synchondroses are mentioned for cranial vault, cranial base, nasomaxillary complex, and mandible with specific roles described for each.

Growth Processes

• Deposition: Addition of new bone is a component of bone growth processes
• Resorption: Bone removal is a bone growth process.
• The surface of bone facing the direction of growth shows deposition and the opposite surface facing away undergoes resorption.

Growth Fields

• Outer and inner surfaces of bones display mosaic-like growth patterns.
• Growth activity can be either depository or resorptive, with opposing fields often characterized by opposite activity.
• The irregularities in growth activity are a result of varied functions imposed by attachments on the bone.

Growth Sites and Centers

• Growth fields important for bone growth are the periosteal/sutural bone-forming areas like mandibular condyle, maxillary tuberosity and synchondroses in the basicranium and sutures.
• The alveolar process is a specific growth site.
• A growth center is where growth is independent.
• The center is a specific location where growth occurs.

Basic Phenomena Involved in Growth Mechanisms

• Conversion of cartilage (synchondroses, nasal, condylar cartilage) is a crucial growth mechanism.
• Sutural deposition contributes to bone growth.
• Periosteal remodeling is relevant to bone growth.

Synchondroses

• Temporary bands of cartilage found at the junctions of bones of endochondral origin.
• Considered as the growth centers and pacemakers of the cranial base.
• Some, like the spheno-occipital synchondrosis, persist postnatally.

Nasal Septal Cartilage

• Plays a crucial role during prenatal and early postnatal growth of the middle face.
• Important in maxilla growth.
• Occupies a unique position when it pushes the maxilla forward and downward.

Conylar Cartilage

• A type of cartilage which plays an essential but secondary role in the mandible's growth in relation to adaptation.

Sutures

• Vital for craniofacial growth as they allow limited movements in the united bones, act as growth areas, and absorb mechanical stresses.
• Sutures are composed of three or five layers: proliferation zone separating two bones, with a fifth connective tissue layer contributing towards slight adjustments during growth.

Periosteum

• An osteogenic zone.
• Plays a significant role in altering bone size and shape.
• Matrix producing/ proliferating cells respond to mechanical forces, with tension promoting bone deposition and pressure inhibiting it.

Growth Pattern

• Describes changes in the size and shape of a bone.
• It involves two primary processes: modeling and remodeling.

Modeling

• Independent resorption and formation sites modify bone shape, size, or both.
• Bone modeling is crucial for shaping bones and adaptation to external loads (e.g., head-gear therapy).

Remodeling

• A coupled sequence of resorption and formation to replace previously existing bone.
• This process continually adjusts the bone's structure.
• Remodeling modifies bone's shape and size subtly as it adapts to its environment.

Relocation

• Progressive and sequential movement of component parts as a bone enlarges.
• The basis for remodeling in bones.

Types of Remodeling

• Biochemical: Maintains calcium levels.
• Secondary: Rebuilds cancellous bone with Haversian systems.
• Pathological: Occurs after disease or trauma.
• Growth: Necessary for adjustments during growth.

Functions of Remodeling

• Relocating components throughout the bone
• Adapting bone shape for various different functions.
• Modifying bone size.
• Fine-tuning the fit between various bones..
• Responding to changing conditions.

Enlow's V-Principle

• One of the fundamental concepts of facial growth.
• Many facial and cranial bones exhibit a V-shaped configuration.
• Bone deposition (growth) occurs on the inner side of the V and resorption on the outer.
• Growth proceeds towards the wider end of the V.

Examples of V-principle application:

• Bone deposition on the lingual side of coronoid processes results in growth and increase in that part of the ramus.
• Bone growth produces a posterior direction in coronoid processes.
• Applying the V-principle to the mandible results in increases in posterior and superior directions.
• Applying the principle to the maxilla causes an increase in the transverse dimension and consequently increases the airway space.

Growth Movements:

• Cortical drift: Bone relocation/ shifting of an enlarging portion of the bone by the remodeling of its osteogenic tissues.
• Displacement: Physical movement of the entire bone as a single unit. This takes place at points away from the bone's enlargement.

Primary Displacement

• Bone growth occurs via surface deposition; other bones in direct contact shift away.
• The force of growing soft tissues around the bone pushes it away from surrounding parts, creating space for enlargement.

Secondary Displacement

• The movement of bones caused by separate enlargements of other nearby or distant bones.
• Result of bone enlargement occurring in adjacent and soft tissues, and transmitted to other, adjacent parts.

Age Equivalence

• Due to variations, individuals at the same chronological age can differ in maturation and size.
• Biologic age is more appropriate for comparison.
• Skeletal and dental ages are used for comparing growth.

Growth Timing

• Timing variations in growth are because of differences in individuals' biological clocks.
• It is genetically controlled, as reflected in sex-related and environmental differences.

Growth Spurts

• Periods of accelerated growth.
• Related to hormonal alterations.
• Timing varies based on sex. There are normal infantile, juvenile, and pubertal growth spurts. Timing occurs at specific ages.

Changing Concepts and Hypotheses of Craniofacial Growth

• Various theories regarding facial growth have evolved over time, including remodeling, genetic, sutural, Scott’s, functional matrix, van Limborgh’s, servosystem, and growth relativity theories.

Bone Remodeling Theory (Brash 1930)

• Bone growth is primarily by apposition on surfaces.
• Jaw growth occurs through bone deposition at posterior surfaces.

Conclusion

• Malocclusion and facial deformities often arise from deviations in the normal developmental processes.
• Understanding facial growth is crucial for effective orthodontic treatment.

References

• Lists of researchers, their articles, and editions of books pertinent to facial growth studies are presented.

Test your knowledge on the various theories of craniofacial growth including Hunterian growth, remodeling theory, Genetic Theory, and the Sutural Hypothesis. This quiz will challenge your understanding of the roles of jaws, sutures, and cartilages in craniofacial development.