Concepts of growth& development II
ORTD 431, lecture 4
Pages 35-48, 94-98, 108-112 3rd addition Proffit
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The Nature of Skeletal Growth
 At the cellular level , there are only three
possibilities for growth
1. Hypertrophy
increase in cell size
2. Hyperplasia
increase in cell No.
3. Secretion of extracellular matrix (ECM)
 In fact all three processes occur in the skeletal
growth where hyperplasia is the most prominent
followed by hypertrophy then EMC
 Secretion of ECM is most important in skeletal
system growth
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 Thus there is a distinction between growth of soft or
non mineralized tissue and hard , calcified tissues.
 Hard tissue includes ( bone, teeth and sometimes
cartilages)
 Soft tissues are every thing else
 In most instance cartilage behaves like soft tissue
and should be included in soft tissue group
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Interstitial Growth
- Growth of soft tissues occurred by
combination of hyperplasia and hypertrophy
this phenomenon go every where within the
tissues the result is interstitial growth
- It occurs in at all points within the tissue
- Is characteristic of nearly all the soft tissues
and of uncalcified cartilage within the skeletal
system.
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Direct or surface apposition of bone
• Appositional growth growth by addition at
the periphery of a particular part.
• Interstitial growth that occurring in the
interior of structures already formed.
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 The periosteum play an important role in
adding thickening of bone and reshaping the
outer contour of bone.
 As long as the rate of proliferations of
cartilage cells equal or faster than maturation
and secretion of ECM are high , there is
growth as they slow growth will slow too
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The nature of skeletal growth
In general bone formation in the body occurs
primarily through two main scenarios:
1.Endochondral bone formation ( a transitional
cartilage is formed).
Sites: chondrocranium and long bones.
2.Intramembranous bone formation no cartilage
model (direct apposition of bone in the ECM).
Sites : mandible, maxilla, and cranial vaults.
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Remodeling
Growth process by which apposition (bone
addition) takes place in one area and resorption
( bone removal) takes place in another area.
Function of remodelling :
1- Create the changing size of the whole bone.
2- Relocate each parts of the whole bone to
allow bone enlargement.
3- Shape the bone to accommodate its
functions.
4- Provide fine tune fitting to all bone parts to
each other and to the surrounding soft tissues.
5- Carry out continuous structural adjustments
to adapt to intrinsic and extrinsic changes in
condition.
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Development of mandible
 In the mandible , bone formation begins just
lateral to meckels cartilage and spreads
posteriorly along it without any direct
replacement of the cartilage by the newly
forming bone of the mandible .
 Meckels cartilage disintegrate except some
remnants which stay as
1. Sphenomandibular ligaments
2. Tow of conductive ossicles.
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The condylar cartilage ( secondary cartilage)
develops initially as a separate area of
condensation from that of the body of the
mandible , and only later is incorporated
within it. Fusion of the cartilage with the
mandibular body occurs at 4 months . But the
condylar cartilage persists after birth.
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Development of Maxilla
The maxilla also forms initially as mesenchymal
condensation lateral to the nasal capsules . The
growth cartilage contribute to lengthening of
the head and anterior displacement of the
maxilla.
An accessory cartilage ( zygomatic or
molar cartilage), which forms in the developing
malar process , disappears and is totally
replaced by bone before birth
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Site and types of growth in the
craniofacial complex
 To understand growth in any area of the
body , it is necessary to understand:
1. Site or location of growth
2. Type of growth occurring on that location
3.The determinant or controlling factors in that
growth
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The site growth in craniofacial complex
1) The cranial vault , the bone that cover the
upper and outer surface of the brain
2) The cranial base , the bony floor under the
brain, which is also the dividing line between
the brain and the face.
3) The nasomaxillary complex made up from
the nose, maxilla, and associated small
bones
4) The mandible
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Cranial Vault
 Bone formation occurs via intramembranous
pathway ( by periostum)
 At birth, the flat bones of the skull are widely
separated by relatively loose connective tissues
the Fontanelles allows a considerable
deformation of the skull at birth
this allows
the relatively large head to pass through the birth
canal.
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Cranial Vault
 After birth, apposition of bone along the edges of
Fontanelles.
 Remodeling at the sutures is the major
mechanism for growth of the cranial vault.
 In addition there is tendency for remodeling on
the outer & inner surfaces of the flat bone ,
which allows changes in the contour during
growth.
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The Cranial Base
 Bony floor under the brain
 Bones are formed initially in cartilage and
later transformed by endochondral
ossification to bone.
 In general, cranial base is a midline structure
grow throw the endochondral pathway
(cranial base )and as you move laterally ,at
sutures and surface remodeling become more
important.
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The Cranial Base
• At synchonrosis , a band of immature
proliferating cartilage cells is located between
the centers of ossification.
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Growth at intersphenoid synchonrosis
A band of immature proliferating cartilage cells is
located at the center of the synchonrosis, while a
band of maturing cartilage cells extend in both
directions away from the center , and endochondral
ossification occurs at both margins.
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The cranial base
 Growth at the synchondrosis lengthens this
area of cranial base .
 Even within cranial base , bone remodeling
on surface is also important it is the
mechanism by which the sphenoid sinus
enlarges, for instance.
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Maxillary (nasomaxillary complex) growth
 The maxilla develops postnatally entirely by
intermembanous ossification.
 No cartilage replacement
 Growth occur in two ways:
1) Apposition of new bone at the sutures.
2) Surface remolding .
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Maxillary (nasomaxillary complex) growth
 As growth of the surrounding soft tissues
translates The maxilla downward and forward
, opening up Space at its superior and
posterior sutural attachments, new bones is
added on both sides of sutures.
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Mandible
 Hyperplasia, hypertrophy, and endochodral replacement occur in the
condylar cartilage
 all other areas of the mandible are formed by direct surface
apposition and remodeling.
The chin moves downward and forward.
The correct concept of mandibular growth is that the mandible
translated downward and forward and grows upward and backward.
 the actual growth occurs at condyle and along the posterior surface
of the ramus (removal of bone from anterior surface of ramus and
deposition of bone on the posterior surface make the mandible grow
longer
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Theories of growth
 Three major theories in recent years have attempted to
explain the determinants of craniofacial growth:
1) Bone , like other tissues, is the primary determinant
of its own growth
2)Cartilage is the primary determinant of skeletal
growth ,while bones responds secondarily and
passively.
3) The soft tissue matrix in which the skeletal
elements are embedded is the primary determinant
of growth , and both bone and cartilage are
secondary followers.
 Sites Vs. center of growth
 Functional matrix theory.
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