Growth of skull & jaws

1. Growth of Skull & Jaws
Dr.Noor AlTamimi

2. • Endochondral and Intramembranous ossification
• Types of cartilaginous growth
• Synchondroses
• Growth of condylar cartilage
Contents

3. Skull Growth
• There are several interrelated factors determine
the growth of skull & jaws.
• General Effects: which influence the overall
shape & growth rate of bones include:
Hormonal influences
Nutritional influences
Genetic influences
Socio-economic influences

4. • Local effects:
 The growth pattern followed by a particular part.
 The effect of enclosed tissues (Capsular Matrices) on the adjacent
bones.
 Muscle attachments, joints, adjacent soft tissues influence the
detailed architecture of bones (Periosteal Matrices)

5. Bone Formation
• There are two types of bone formation and both
start with coalescence of mesodermal or
ectomesenchymal cells into dense groups in a
process known as Condensation.

6. • Endochondral ossification (ECO):
When the condensed mesenchymal cells
differentiate into chondroblasts which form a
cartilaginous template of the bone and the
subsequent replacement of cartilage tissue by
bone.

7. • Cartilage replacing bones those that
develop by ECO include post cranial
skeleton - except the clavicles – plus the
cranial base.

8. • Intramembranous ossification (IMO):
The direct conversion of mesenchymal
tissue into bone with no catrilaginous
precursors.
• Dermal bones which mineralize by IMO
inlcudes the cranial vault, lower jaw, facial
skeleton & the clavicles

9. Cranial vault are formed by IMO and follow
Neural growth pattern.
Facial skeleton undergo IMO and follow
Somatic growth curve.
Cranial base develop by ECO and conform
Neural growth then adjust to somatic growth
pattern.

10. Cartilaginous Growth
Appositional growth
results in the increase of the diameter or
thickness of the cartilage. The new cells derive
from the perichondrium and occur on the surface
of the cartilage model

11. Interstitial growth
results in an increase of cartilage mass and
occurs from within. Chondrocytes undergo
mitosis within their lacuna, but remain
imprisoned in the matrix, which results in
clusters of cells called "isogenous groups."

13. Synchondroses
• are the cartilaginous joints of the skull which
form when neighboring centers of ossification
within a continuous mass of hyaline cartilage
enlarge and encroach upon each other.
• Cranial base synchondroses are important
growth centers of the craniofacial skeleton and
the last sites in the cranium to terminate growth.

14. HISTOLOGICAL
STRUCTURE
Progenitor zone
Proliferative zones
Hypertrophic zone

16. • Spheno-ethmoidal synhondrosis:
 An active growth site prenatally, but the
cartilage is replaced by fibrous tissue shortly
after birth where growth continues after its
conversion to a suture.
Ossification at this synchondrosis contributes to
the enlargement of the cranial base anterior to
the pituitary fossa.

17. • Spheno-occipital synchondrosis
Principal site of elongation of the basicranial axis
& growth continues until early teens.
The joint is grown over, starting on the
intracranial surface & is completely obliterated at
maturity, no joint is visible between the sphenoid
& occipital bones after this age.

18. Growth of the Mandible
• By 6 weeks of development, Meckel’s
cartilage forms a rod of cartilage stretching
from the otic capsule to the midline in each first
pharyngeal arch. The anterior ends of the two
cartialges are united by a bridge of
ectomesnchyme.

19. The Mandible is a Dermal bone which develop in close association with,
but not from Meckel’s cartilage.

20. • By 7 weeks, ossification center appear in the V
of the mental & incisive nerves of each half of
the mandible, then it spreads anteriorly &
posteriorlly on the lateral aspect of the nerves &
the mandible. Then it spreads beneath these
structures & spreads upward to form a U shape
enclosing the teeth & nerves.
• The U is later roofed front to back to form the
Mandibular canal.

21. • The Body of the mandible is produced by
single center of ossification & runs from the
anterior midline symphysis to the area which will
become the mandibular foramen.
As the body of the mandible grows it will contact
Meckel’s cartilage & causes its resorption.

22. • The ramus is formed by 10th
week by rapid backward
spread of ossification,
rudementary backward
pointing coronoid & condyalr
processes are visible.The
part of Meckel’s cartilage
lying medial to the ramus is
resorbed, but its
perichondrium remains as
the Sphenomandibular
ligament.

23. • Secondary cartilages are cartilages that
appear in the mandible - which shouldn’t
happen since it’s a dermal bone –
• are derived from cell lines which have
already differentiated to produce dermal
bone.
• Growth sites producing bone by ECO

24. 3Secondary
Cartilages
2Cartilages in the Ramus
-Condylar Cartilage
-Coronoid Cartilage Symphyseal cartilages

25. Condylar Cartilage
The largest & most important one, appears at 12
weeks on the superior & lateral aspects of the
condylar process.
Active throughout the growth period until
maturity.

26. Undergoes enlargement & forms a conical mass
in the condyalr process, as far as the mandibular
foramen. As the cartilage grows it’s replaced
inferiorly by bone.
By 5 months, much of the original cartilage has
ossified, leaving a narrow zone of growth
cartilage persisting beneath the articular surface
of the condylar head of the mandible.

28. Coronoid Cartilage
Appear at 12 weeks as a cartilaginous strip on
the anterior bordeer of the summit of the
coronoid process, but ceases activity &
disappears within weeks

29. Symphyseal cartilages
Small nodules of secondary cartilage which
develop in the midline symohysis .
The mandible at birth is still separated into right
& left halves by the mental symphysis which
fuses at abut the end of the 1st
post natal year as
the cartilages ossify.