Lecture 5: Growth and Facial Development

Why are soft tissues considered poorly studied in growth?

Because most research focuses on bone behavior, while soft tissues adapt secondarily and are harder to quantify

What are the two major categories of bone behavior in growth?

Bone development (genetic) and soft tissue adaptation (environmental)

What environmental factor is highlighted as influencing mandibular growth?

Mouth breathing

What are the two major types of bone growth?

Endochondral and intramembranous.

What type of bones grow via endochondral ossification?

Long bones and the cranial base

What is the key feature of endochondral growth?

Replacement of a cartilage model with bone

What structure drives longitudinal growth in long bones?

The growth plate (epiphyseal plate)

What two factors influence growth plates?

Genetic programming and mechanical stress (pressure/tension).

What is the cranial base composed of?

Chondrocranium — cartilage that ossifies endochondrally

What are the three major cranial base synchondroses?

Spheno-ethmoidal, intersphenoidal, and spheno-occipital

Which cranial base synchondrosis closes last?

Spheno-occipital synchondrosis (12–15 years).

Why is cranial base growth important for facial development?

It influences the cranial base angle, which affects maxillary and mandibular position

What type of bones grow via intramembranous ossification?

Facial bones, cranial vault, mandible (except condyle), and clavicles

What tissue is replaced during intramembranous ossification?

Vascularized mesenchyme → bone

What is the key feature of intramembranous growth?

It causes displacement of adjacent structures as bone expands

What is bone modeling?

The process of shaping bone through apposition and resorption on different surfaces

What is bone remodeling?

The turnover of bone to maintain shape and adapt to function

What is Enlow’s V principle?

A growing bone displaces in space, and to maintain shape, bone is added inside the V and resorbed outside the V.

What does the V principle help predict?

The direction of growth of a bone.

What is drift?

Combined resorption and apposition that moves a bone through space while maintaining shape

What is displacement?

Movement of a bone due to growth of adjacent structures (primary or secondary displacement)

Growth plates are _______ centers of bone elongation.

genetically programmed

_____ can alter mandibular posture.

Mouth breathing

True or False: Growth plates respond to pressure and tension.

True

True or False: The spheno‑ethmoidal synchondrosis closes at 6 years.

True

True or False: Drift allows bones to increase in volume while maintaining shape.

True

True or False: Soft tissues grow independently of bone.

False: they adapt to bone growth

True or False: Cranial base growth has no effect on facial development.

False: it strongly influences facial position and rotation.

Why is endochondral growth highly relevant to dentistry?

The mandibular condyle grows endochondrally, influencing mandibular length and rotation

What happens to cartilage in a growth plate during endochondral ossification?

It is replaced by immature bone, then remodeled into mature bone.

What is the role of mechanical stress in endochondral growth?

Pressure inhibits growth; tension stimulates growth — a key orthodontic principle.

Why is the cranial base angle clinically important?

It influences maxillary projection and mandibular rotation.

Which cranial base synchondrosis closes first?

Intersphenoidal synchondrosis (at birth).

What is the first step in intramembranous ossification?

Mesenchymal cells differentiate into osteoblasts.

What is osteoid?

Unmineralized bone matrix secreted by osteoblasts

What happens to osteoblasts once they become trapped in osteoid?

They become osteocytes

What is the difference between bone modeling and remodeling?

Modeling changes shape; remodeling maintains structure

What is the “resorption–apposition” concept?

Bone is removed from one surface and added to another to maintain shape during displacement

True or False: Displacement only occurs from a bone’s own growth.

False: it can be primary or secondary.

Why is drift essential for craniofacial development?

It allows bones to increase in volume, change shape, and move spatially without distorting anatomy

What is primary displacement of bone?

Movement of a bone due to its own growth

What is secondary displacement of bone?

Movement of a bone due to growth of neighboring bones

What is the clinical significance of displacement?

It explains how the maxilla and mandible move forward and downward during growth.

What is the relationship between cortical and cancellous bone in growth?

Cortical bone provides shape and strength, while cancellous bone allows rapid turnover and remodeling

Why is cortical bone important in orthodontics?

It determines resistance to tooth movement and anchorage

What is the significance of high‑density cortical bone in the mandible?

It makes mandibular tooth movement slower and requires greater force control

What is the “wall and platform” analogy in Enlow’s text?

Bone is resorbed on one side and added on the other, like a wall being rebuilt while the platform moves forward

What is the effect of growth on the mandibular ramus?

Posterior apposition and anterior resorption allow the ramus to move posteriorly while increasing height

What is the effect of growth on the mandibular body?

Lingual resorption and buccal apposition expand the arch and reposition teeth

What is the effect of growth on the nasal cavity?

Enlargement via lateral wall resorption and midline apposition

What is the effect of growth on the palate?

Lateral drift and lateral expansion

What is the effect of growth on the alveolar process?

It grows in response to tooth eruption, not independently

Why is the alveolar process considered “tooth‑dependent”?

Without teeth, the alveolar bone does not develop and resorbs

Drift is the combination of ____ and _____

resorption; apposition

Cortical bone provides ____ and _____

strength; shape.

_____ bone allows rapid turnover.

Cancellous

What is the effect of drift on the palate?

The palate drifts inferiorly, increasing vertical facial height.

What is the effect of drift on the nasal cavity?

Lateral wall resorption enlarges the nasal cavity

What is the effect of drift on the orbits?

Posterior resorption and anterior apposition move the orbits forward as the face grows

What is the effect of drift on the zygomatic bone?

Posterior resorption and anterior apposition move the zygoma forward and outward.

What is the effect of drift on the mandibular ramus?

Posterior apposition and anterior resorption reposition the ramus posteriorly while increasing height

What is the effect of drift on the chin (pogonion)?

Anterior apposition and posterior resorption move the chin forward.

What is the effect of drift on the maxillary tuberosity?

Posterior apposition lengthens the dental arch for molar eruption

What happens to alveolar bone if a tooth is congenitally missing?

The alveolar ridge fails to develop and may resorb

What is the effect of growth on the midface?

Downward and forward displacement due to cranial base growth and maxillary remodeling.

What is the effect of growth on the mandible?

Downward and forward displacement due to ramus remodeling and condylar growth.

What is the effect of condylar growth on mandibular position?

It lengthens the mandible and influences jaw rotation

What is the effect of posterior ramus apposition?

Moves the mandible posteriorly while increasing ramus height.

What is the effect of anterior ramus resorption?

Allows the mandible to translate forward during growth.

Wxhat is the effect of inferior border apposition?

Increases vertical facial height

What is the effect of superior border resorption?

Maintains mandibular shape while allowing vertical growth

What is the effect of maxillary sutural growth?

Moves the maxilla downward and forward

Why are sutures considered growth sites rather than growth centers?

They respond to functional demands and adjacent growth, not intrinsic genetic programming like growth plates

What is the clinical significance of sutural growth?

It drives cranial vault expansion and contributes to midface displacement

What is the difference between a growth site and a growth center?

Growth centers are genetically programmed (e.g., synchondroses); growth sites respond to environmental and functional forces (e.g., sutures)

What is the primary growth center of the cranial base?

The spheno‑occipital synchondrosis

What is the primary growth site of the maxilla?

The circummaxillary sutures

What is the primary growth site of the mandible?

The condylar cartilage (endochondral)

What is the role of the condyle in mandibular growth?

It provides vertical and anteroposterior lengthening of the mandible

Why is the condyle considered an adaptive growth site?

It responds to functional loading, posture, and occlusion

What is the effect of condylar growth on mandibular rotation?

It influences whether the mandible rotates clockwise or counterclockwise