Lecture 14 & 15 Postnatal Craniofacial Growth 2026

What is growth (general definition)?

An increase in size, or more precisely an increase in at least one measurable dimension, via increase in cell number, cell size, or increase in mass of non-cellular substances

What is biological growth?

The irreversible, permanent increase in the size, mass, or volume of an organism over a specific period

What are the three cellular mechanisms of biological growth?

Hyperplasia (increase in cell number), hypertrophy (increase in cell size), and accretion (accumulation of non-cellular materials like bone matrix)

What is hyperplasia?

An increase in cell number

What is hypertrophy?

An increase in cell size

What is accretion?

Accumulation of non-cellular materials, such as bone matrix

Is biological growth measurement value-neutral or value-laden?

Value-neutral; it is easily quantifiable using standard physical metrics

What is determinate growth?

Growth that ceases once the adult state is attained (typical of many animals, including humans)

What is indeterminate growth?

Growth that continues indefinitely throughout life, seen in some organisms like plants or fish

What does facial growth require, according to the lecture?

Intimate morphogenic interrelationships among all component growing, changing, and functioning soft and hard tissue parts; no part is developmentally independent and self-contained

What is the growth process in the face working toward?

An ongoing state of composite functional and structural equilibrium

What is development?

The process of progressive, orderly functional and structural changes that occur over an organism's lifespan; focuses on increasing complexity, specialization, and maturity

How does growth differ from development in nature of change?

Growth is quantitative (adding cells and mass); development is qualitative (gaining new abilities, shapes, and functions)

What is the timeline of growth vs development?

Growth is determinate, usually stopping at adult maturity; development is a continuous, lifelong process until death

What are the underlying processes of growth vs development?

Growth: cell division (mitosis), cell enlargement, accretion of intercellular substances. Development: gene expression, tissue differentiation, organogenesis, neuro-motor maturation

What is endochondral ossification?

Bone formation occurring by formation of a cartilaginous model that is gradually replaced by bone

Where does endochondral ossification occur in the craniofacial skeleton?

Basal part of the skull and long bones

What happens to residual cartilage after endochondral ossification?

It gives rise to the articular cartilage or the growth plate between the epiphysis and diaphysis of long bones

What is intramembranous ossification?

Bone formation that occurs when mesenchymal cells differentiate directly into osteoblasts and deposit bone matrix within connective tissue, with no intermediate cartilage formation

Where does intramembranous ossification occur in the craniofacial skeleton?

Cranial vault and both jaws

When does intramembranous ossification begin in development?

Around week 6

In intramembranous ossification, what do ossification centers merge to form, and what do those merge into?

Ossification centers merge to form a trabecula; trabeculae merge to form spongy bone

What are the endochondral elements of the craniofacial skeleton (per the diagram)?

Temporal bone, occipital bone, condyle, zygomatic bone, auditory ossicles (malleus, incus, stapes)

What are the intramembranous elements of the craniofacial skeleton (per the diagram)?

Frontal bone, parietal bone, nasal bone, maxilla, mandible

What structures act as bidirectional, primary cartilage growth plates that elongate the neurocranium floor?

The spheno-occipital and intersphenoid synchondroses of the cranial base

What role does the nasal septal cartilage play in craniofacial growth?

It acts as a primary cartilage growth center, serving as a biological "pacemaker" that physically expands and thrusts the entire midface and maxilla forward and downward during childhood

What kind of growth center is the mandibular condylar cartilage?

A secondary cartilage growth center; it does not develop from the original embryonic chondrocranium but forms independently within the intramembranous mandibular ramus, allowing upward and backward growth

How does the cranial vault (calvarium) grow?

Sutural growth driven primarily by physical expansion of the brain (tension in sutural membranes), supplemented by periosteal apposition on outer surfaces and remodeling resorption on inner surfaces

How does the nasomaxillary complex (maxilla) grow?

Entirely intramembranously; primary bone apposition occurs at the circummaxillary sutures and posterior maxillary tuberosity, pushing (displacing) the maxilla anteriorly and inferiorly relative to the cranium

How does the mandibular body form?

Via intramembranous ossification (main body and ramus)

Why can't hard (mineralized) tissue grow interstitially?

Once mineralization takes place, interstitial growth becomes impossible; bone can only grow by direct addition of new bone to the surface of existing bone via periosteal cells (surface apposition)

How does soft tissue growth occur?

By a combination of hyperplasia and hypertrophy, resulting in interstitial growth

What is appositional growth?

Growth occurring at outer/inner tissue surfaces (periosteum/endosteum) via surface deposition by specialized cells

What is interstitial growth?

Growth occurring deep within the interior of a tissue via mitotic division of internal cells (e.g., chondrocytes)

Does appositional growth occur in bone?

Yes; it increases width/diameter throughout life

Does interstitial growth occur in bone?

No; rigid mineralized bone matrix cannot expand internally

Does appositional growth occur in cartilage?

Yes; it adds width at the edge

Does interstitial growth occur in cartilage?

Yes; it lengthens/expands the cartilage model from within

What are the three measurement (observational) approaches for studying growth?

Longitudinal studies, cross-sectional studies, and mixed longitudinal studies

What is a longitudinal study of growth?

A group of children examined repeatedly over a long period during active growth; valuable for growth rates and individual variability, but difficult to retain subjects and requires long data collection

What is a cross-sectional study of growth?

A large number of individuals of different ages examined once to obtain growth information at particular ages; allows estimation of mean population growth rate quickly, but rate/velocity standards can only come from longitudinal studies

What is a mixed longitudinal study?

A combination of cross-sectional and longitudinal designs; subjects of different ages are each examined for a short period of time (e.g., studying birth-to-21 growth in only 6 years using overlapping age cohorts)

What is craniometry?

Precise measurements done on dry skulls, used to study skeletal remains of human ancestors and growth patterns of extinct populations

What is anthropometry?

Measurements of skeletal dimensions on living individuals using landmarks established from dry skull studies, using overlying soft tissue points; repeated measurements produce longitudinal data

What are key features of cephalometric radiology?

Head is precisely oriented before radiograph, radiographic magnification is controlled, allows direct measurement of bony skeletal dimensions, but produces a 2D representation of a 3D structure

What is an advantage of 3D cephalometry over traditional 2D cephalometric radiology?

It avoids the limitation of representing a 3D structure in only two dimensions

List the cross-sectional vs longitudinal tradeoffs in duration.

Cross-sectional: short duration of study. Longitudinal: longer duration of study (years)

List the cross-sectional vs longitudinal tradeoffs in variability and sample size.

Cross-sectional: variability within sample can conceal growth details, uses large sample size. Longitudinal: shows individual variations in growth curve (especially timing), uses small number of subjects

What can cross-sectional studies estimate that longitudinal cannot, and vice versa?

Cross-sectional allows estimation of mean rate of growth; longitudinal allows accurate prediction of adult height

What is the distance curve (cumulative curve)?

A growth curve created by plotting size attained as a function of age; data can be derived from cross-sectional or longitudinal studies

What is the velocity curve (incremental curve)?

A growth curve indicating the rate of growth over a period, showing the increment added each year; data are derived from longitudinal studies only

On a classic height distance/velocity curve, what happens around age 14 in the example shown?

An acceleration of growth (adolescent growth spurt) is seen as a peak in the velocity curve

What are the three experimental approaches for studying growth?

Vital staining, radioactive tracers, and implant radiology

What is vital staining used for in growth studies?

Uses dyes (e.g., alizarin red, tetracycline) that stain mineralizing tissues; injected into a living animal, deposited in bones/teeth, and detected later after sacrifice of the animal

What can tetracycline staining reveal clinically about a child's growth history?

Because tetracycline deposits in mineralizing tissue at the time of administration, the location of staining in tooth crowns can reveal when in development (e.g., age) high doses were given

What is the radioactive tracer method for studying growth?

Radioactive tracers (e.g., Technetium 99mTc) label metabolites incorporated into tissues, detecting areas of rapid growth in humans (diagnosing localized growth problems) or via autoradiography in animal studies

What is implant radiology (the Björk method)?

A method developed by Professor Björk using inert metal pins implanted permanently into bones (including face/jaws) to allow precise superimposition of cephalometric radiographs, revealing relative bone positions and contour changes over time

What are the three important concepts in the study of growth (per this lecture)?

Pattern of growth, growth variability, and timing

What does "pattern of growth" refer to?

A complex set of proportions; the schematic changes in overall body proportions during normal growth and development (e.g., from fetus to adult)

What condition is described as the most common form of dwarfism, primarily affecting the long bones?

Achondroplasia (about 1 per 26,000 live births)

What are clinical features of achondroplasia?

Limbs disproportionately shorter than the trunk, bowed limbs, increased lumbar lordosis, and a face that is small relative to the head

What is the cephalocaudal gradient of growth?

An axis of increased growth extending from the head toward the feet; applies to craniofacial growth and skull proportion changes from birth to adulthood

According to Scammon's curves, when is growth of neural tissue nearly complete?

By about 6 or 7 years of age

According to Scammon's curves, what pattern do general body tissues (muscle, bone, viscera) follow?

An S-shaped curve, with a definite slowing during childhood and acceleration at puberty

According to Scammon's curves, how do lymphoid tissues grow?

They proliferate far beyond the adult amount in late childhood, then undergo involution

According to Scammon's curves, when does genital tissue growth accelerate?

Rapidly, at the same time lymphoid tissue undergoes involution (around puberty)

Does mandibular growth follow the general body curve or the neural curve more closely?

The mandible follows the general body curve more closely than the maxilla; the pubertal acceleration in general body growth parallels the increase in sexual organ development

Why is growth variability clinically important?

It is important to recognize abnormal or pathologic growth by comparing a child to peers on a standard growth chart/norms for height, weight, skeletal, and dental development

How is the "normal range" typically defined statistically on growth charts?

Measurements falling within one standard deviation around the mean, corresponding to between the 16th and 84th percentile

Are patients who fall outside the normal growth range necessarily abnormal?

No; they are unusual but not necessarily abnormal

What is a "distance curve" used to construct height growth standards?

A curve built from data on large numbers of subjects, differing between males and females, used separately in clinical applications

When does the adolescent growth spurt begin in females vs males?

Females: about 10.5 to 11 years. Males: about 12.5 to 13 years. Duration is about 2 to 2.5 years in both sexes

In girls, when does menarche occur relative to peak height velocity?

Menarche always follows the peak velocity of the adolescent growth spurt in height

How does weight growth variability compare to height?

There is more variation in weight measurements than height measurements

When is the average adolescent weight spurt in girls vs boys?

Girls: about 12 years. Boys: about 14 years

How does the peak velocity of the weight spurt relate to the height spurt?

The peak velocity for weight spurt lags behind the peak velocity for height by an average of 3 months

What does "timing" mean as a concept in growth variability?

Variation that arises because the same growth events happen at different times in different individuals (e.g., the adolescent growth spurt occurring earlier or later)

What tends to happen with early-maturing vs late-maturing children over time?

Early-maturing children grow rapidly and appear large on developmental charts until growth ceases; late-maturing/slow-growing children initially appear behind but eventually catch up and may surpass the early maturers

How does the intensity of the adolescent growth spurt relate to its timing?

The earlier the adolescent growth spurt occurs, the more intense it appears to be

When using menarche as a zero time reference point, how do velocity curves compare between early and late maturers?

The growth pattern in each case is quite similar, with almost all variation resulting from differences in timing rather than pattern

Why is chronologic age not always a good indicator of individual growth status?

Because of timing and variability, so biologically measured (developmental) age is more meaningful; developmental age is a more reliable expression of individual growth status

What is morphologic age?

A maturity indicator based on height, comparing a child's height to same-age and other age groups; useful from late infancy to early adulthood

What is sexual age?

A maturity indicator based on the development of secondary sex characteristics; useful only for adolescent growth

What is skeletal age?

A maturity indicator determined by assessing development of cervical vertebrae or bones of the hand and wrist, from appearance of calcification centers to epiphyseal plate closure

Why is skeletal age considered the gold standard for tracking physical maturation?

It directly reflects somatic growth and is highly correlated with height velocity, pubertal growth spurts, and long bone development

What atlas/method is commonly used to evaluate hand-wrist radiographs for skeletal age?

Greulich and Pyle's Radiographic Atlas of Skeletal Development of the Hand and Wrist (1959); also Fishman's method of radiographic skeletal maturation evaluation

What is the Cervical Vertebral Maturation (CVM) method?

A method with five developmental stages (CVMS I through CVMS V) based on morphological features of the bodies of C2, C3, and C4, used to assess skeletal maturity from a single cephalogram

Between which CVMS stages does the peak in mandibular growth occur?

Between CVMS II and CVMS III

What is dental age based on?

Two methods: observation of age at eruption of primary and permanent teeth (tooth eruption age), and rating of tooth development from crown calcification to root completion using x-rays of developing teeth

How well does dental age correlate with skeletal maturity indicators?

Poorly correlated with general body height, weight, and skeletal maturity indicators

What is a limitation of chronological age as a maturity indicator?

It is strictly time-based from birth date and does not reflect a child's true physiological or developmental maturity level

What are the three (four) major theories that attempt to explain determinants of craniofacial growth?

Sutural Growth Theory, Primary Cartilage Theory, Functional Matrix Theory, and Servosystem Theory

What is a "site" of growth?

A location at which growth occurs passively, reacting to other determinants; there is no tissue-separating force (e.g., condyle, sutures)

What is a "center" of growth?

A location at which independent, genetically controlled growth occurs; it is a growth initiator and tissue-separating force that pushes tissues apart (e.g., craniofacial synchondrosis, nasal cartilage)

Who introduced the Sutural Growth (Suture) Theory and when?

Sicher, in 1952

What did Sicher hypothesize in the Sutural Growth Theory?

That osteogenesis of the chondrocranium and desmocranium is genetically controlled and sutures are the dominant tissue structures; pressure from new bone formation at synchondroses, sutures, and the mandibular condyle pushes bones apart, making these sites both sites and centers of growth

What evidence argues against sutures being true growth centers?

Transplantation experiments show sutures fail to grow after being transplanted to other locations, and sutures respond (react) rather than act independently when pushed or pulled, altering their growth pattern

Who developed the Primary Cartilage Theory?

Scott

What does the Primary Cartilage Theory state?

That cartilage and periosteum are growth centers and sutures are passive; cartilage does the growing while bone merely replaces it. The mandibular condyle was considered the pacemaker for mandibular growth

Is the mandibular condyle analogous to an epiphyseal growth plate, according to modern experiments?

No; although the analogy (condyle as epiphysis-like structure) is attractive, modern experiments indicate it is incorrect