Postnatal growth of the skull and jaws _ Dr. Nabil Al-Zubair

POSTNATAL GROWTH
of
THE SKULL and JAWS
Dr. Nabil Al-Zubair

• What initiates growth?
• What controls the extent & timing of growth?

What initiates growth?
Somatotrophin hormone
(growth hormone)
released from the pituitary gland

What controls the extent & timing of growth?
• Highly conserved homeobox genes
provide the genetic “blue print” for
growth & development
• These genes are the same in all
animals & are highly conserved
• Gives rise to family resemblance – a
disturb of the genes can cause
chromosome defects such as Trisomy
21 (Down’s syndrome)
Genetic control Environmental control

What controls the extent & timing of growth?
• Psychological stress in emotionally
deprived children inhibit the release
of growth hormone
• Moss’s functional matrix theory
Genetic control Environmental control

Mechanisms of bone growth
Bone deposition & resorption
Cortical drift
Displacement

(1) Bone deposition & resorption
• Bone changes in shape & size by two basic
mechanisms
(1) bone deposition &
(2) bone resorption
• The process of bone deposition & resorption
together is called
“Bone Remodeling”

Bone deposition & resorption
The changes that bone deposition &
resorption can produce are:
a. Change in size
b. Change in shape
c. Change in proportion
d. Change in relationship with
adjacent structures

(2) Cortical drift
• A combination of bone deposition &
resorption resulting in:
a growth movement towards the depositing
surface is called
“cortical drift”
Deposition = Resorption
Thickness of the bone remains constant
Deposition > Resorption
Thickness of the bone increases

• PALATE, where bone is
deposited on the inferior
surface and resorbed from
its superior surface.
 The change in the position of a bony structure owing to
remodelling of that structure is called drift
Examples

1. Primary Displacement:
2. Secondary Displacement
(3) Displacement
It is the movement of the whole bones as a unit
Displacement can be of two types:

a- if a bone gets displaced as a result of
its own growth
b- For example growth of the maxilla at
the tuberosity region results in:
pushing of the maxilla against the
cranial base which results in:
the displacement of the maxilla in a
forward & downward direction
1. Primary Displacement:

2. Secondary displacement:
a- if a bone gets displaced as a
result of growth &
enlargement of an adjacent
bone
b- For example, the growth of the
cranial base causes
the forward & downward
displacement of the maxilla

Osteogenesis
Endochondral bone formation
Intra-membranous bone formation

OSTEOGENESIS
• Bone formation takes place in two ways:
1. Endochondral bone formation
2. Intra-membranous bone formation
The process of bone formation is called osteogenesis

The bone formation is preceded by formation of a cartilaginous
model which is subsequently replaced by bone
Endochondral bone formation occurs as follows
Cartilage Bone

Mesenchymal cells
Chondroblasts
Hyaline cartilage
alkaline phosphatase
The surrounding inter-cellular substance becomes calcified
Thus the nutrition to the cartilage cells is cut off leading to their death
Primary areolaeSecondary areolae
The blood vessels & osteogenic cells
from the preichondrium invade the
calcified cartilaginous matrix
OsteoblastsOsteoid
Calcified to form a lamella of bone
Preichondrium
condensed

• Instead bone is laid down directly in a fibrous membrane
• The intra-membranous bone is formed in the following manner:
• The formation of bone is not preceded by
formation of a cartilaginous model

Mesenchymal cells
Collagen fiber
Enlarge & acquire a basophilic cytoplasm & form osteoblasts
Secrete a gelatinous matrix called osteoid around the collagen fiber
They deposit calcium salts into the
osteoid leading to conversion of
osteoid into bone lamella
osteoid bone lamella
Now another layer of osteoid is secreted & this goes on & on.
Ca++
aggregated

Theories of growth
Genetic theory
Sutural theory
Cartilaginous theory
The functional matrix concept

What is the primary determinant of growth ?
Structures thought to be involved:
Bone
Cartilage
Soft tissue
What are the components which have innate growth potential over which there is
genetic & environmental influence ?
‫فطري‬

• Simply states that all growth is
controlled by genetic influence & is
pre-planned
• One of the earliest theories put
forward
Genetic theory

• Sicher believed that cranio-facial
growth occurs at the sutures
• According to him :
• The sutures had innate growth
potential & that the sutures push
apart the bones → an increase in size
Sutural theory
Old school of thought:

• Disproved by transplanting a suture
→ no sutural growth was produced
• Growth takes place in untreated
cases of cleft palate even in the
absence of sutures
Some points against Sutural theory:

• This theory was put forward by James
Scott.
• According to him:
– intrinsic growth controlling factors
are present in
cartilage & periosteum
with sutures being only secondary
• He viewed the cartilaginous sites
throughout the skull as primary centers
of growth
• Growth of the maxilla is attributed to the
nasal septal cartilage

1. In many bones,
cartilage growth occurs, while bone
merely replaces it
2. Nasal septal cartilage also show
innate growth potential on being
transplanted to another site
Points favour this theory include:

• The functional matrix concept of Melvin
Moss revitalized the studies on growth &
development at a time when the Sutural
growth theory by Sicher & Cartilaginous
growth theory of Scott were severely
criticized for their inadequacy
• The functional matrix concept attempts
to comprehend the relationship b/w
form & function

• The functional matrix hypothesis claims
that:
The origin, form, position, growth &
maintenance of all
(skeletal tissues & organs)
are always
Secondary, compensatory & necessary
response to
Chronologically & morphologically prior events
or processes that occur in
specifically related
(non-skeletal tissues, organs or function
spaces)

• A number of relatively independent function
are carried out in the cranio-facial region of the
human body
• Some of the function carried out include:
(1) respiration, (2) olfaction, (3) vision, (4) hearing,
(5) balance, (5) chewing, (6) digestion, (7)
swallowing, (8) speech & (10) neural
integration
• Each of these functions is carried out by a
functional cranial component

• Each functional cranial component consist
of all of the tissues, organs, spaces &
skeletal parts necessary to carry out a
given function
• The functional cranial component is
divided into:
1. Functional matrix
2. Skeletal unit

Moss’s functional matrix theory
Genetic control is expressed in the soft
tissue
& the cartilage & bone secondarily
Soft tissue
Genetic control
Cartilage Bone
 State that : “growth of the face occurs
as a response to functional needs & is
mediated by the soft tissue in which
the jaws are embedded”
 Brain growth cranium size
 O2 demand Max. sinus
development
 The orbit grows as a result of eye
growth

Enlow’s expanding ‘V’ PRINCIPLE
• Many of facial bones or parts of bone
have a ‘V’ shaped pattern of growth
• The growth movements & enlargement
of these bones occur towards the wide
ends of the ‘V’ as a result of
(1 ) differential deposition &
(2 ) selective resorption of bone

• Bone deposition occurs on the inner
side of the wide end of the ‘V’ & bone
resorption on the outer surface
• Deposition also takes place at the ends
of the 2 arms of the ‘V’ resulting in
growth movement towards the ends
• The ‘V’ pattern of growth occurs in a
number of regions such as the (1) base
of the mandible,
(2) ends of long bones,
(3) mandibular body,
(4) palate etc.,.
+ +- -
++

POSTNATAL GROWTH OF THE
SKULL AND JAWS

MECHANISMS OF BONE GROWTH
Bone grows either by:
1. Replacement of cartilage
(endochondral ossification)
2. Periosteal activity
(intramembranous ossification)

Endochondral ossification-
• This form of bone growth is under tight intrinsic control (genetic).
1. The epihyseal plates of long bones &
•This process is seen in both:
2. The synchondroses of the cranial base.
Spheno-occiptal
Spheno- ethmoidal
Spheno-
occiptal

Intramembranous ossification-
Bone is laid down and resorbed
by
The investing periosteum
and endosteum.
Periosteal remodelling
also needed to
Maintain the overall shape of the bone as it grows

Head
Cranial vault Cranial base
MandibleNaso-maxillary complex

Mechanisms of growthOssification
 Apposition at sutures
 Remodeling due to “ functional matrix” of
expanding brain
Intra-
membranous
Cranial
vault
 Growth centers at synchondrosesEndochondoralCranial base
Growth is directed by
orientation of the sutures
forwards & downwards
 Apposition at
sutures
 Remodeling
 Alveolar
development to allow
eruption of teeth
Intra-
membranous
except for
nasal cartilage
Naso-
maxillary
complex
 Increase in ramal
height by condylar
growth
 Increase in body
height due to Alveolar
eruption of teeth
 2/3 of jaw is completed
at age 10 years
Apposition at sutures
 Remodeling due to “
functional matrices” of
attached muscles
Intra-
membranous
Mandible

Mechanisms of growthOssification
 Apposition at sutures
 Remodeling due to “ functional matrix” of
expanding brain
Intra-
membranous
Cranial
vault
 Growth centers at synchondrosesEndochondoralCranial base
Growth is directed by
orientation of the sutures
forwards & downwards
 Apposition at
sutures
 Remodeling
 Alveolar
eruption of teeth
Intra-
membranous
except for
nasal cartilage
Naso-
maxillary
complex
 Increase in ramal
height by condylar
growth
 Increase in body
height due to Alveolar
eruption of teeth
 2/3 of jaw is completed
at age 10 years
Apposition at sutures
 Remodeling due to “
functional matrices” of
attached muscles
Intra-
membranous
Mandible
Spheno-occiptal
Spheno- ethmoidal
Spheno-
occiptal

Elongation at the synchondroses
• Most of the bones of the cranial
base are formed by a cartilaginous
process
• Later the cartilage is replaced by
bone
• Certain bands of cartilage remain
at the junction of various bones.
• These areas called Synchondroses.
They are important growth sites of
the cranial base
• The important synchondroses found
in the cranial base are:
1. Spheno-occipital synchondroses
2. Spheno-ethmoidal synchondroses
3. Inter-sphenoid synchondroses
4. Inter-occipital synchondroses

Growth centers
(1) Spheno – occipital synchondrosis:
Active until age 16 years
Calcification completed at age 25 years
Spheno-occiptal
Spheno- ethmoidal
Spheno-
occiptal

Cranial Base
• The SOS is anterior to the TMJ but
posterior to the anterior cranial
fossa and its growth influences the
facial skeletal pattern.
• Growth at the SOS
 (1) Increases the length of the cranial
base, and
since the maxilla and mandible are both
relate to this structure, the latter
(2) plays an important part in how
the 2 jaws relate to each other.

Growth centers
(2) Fronto – ethmoidal synchondrosis:
Active until puberty
Spheno-occiptal
Spheno- ethmoidal
Spheno-
occiptal

Growth centers
(3) Spheno – ethmoidal synchondrosis:
Active until age 7 years
Spheno-occiptal
Spheno- ethmoidal
Spheno-
occiptal

Timing of cranial base growth
a. By birth, 55-60% of adult size is attained
b. By 4-7 years, 94% of adult size is attained
c. By 8-13 years, 98% of adult size is attained

The maxillary complex
• The maxilla enlarges AP by
(1) Deposition of bone posterioly at the
tuberosities which enlarge the dental
arches.
(2) Anterior displacement occurs as bone is
laid down on its posterior aspect.
• Downward growth occurs by
(1) development of the alveolar process and
(2) dental eruption, and also by
(3) inferior drift of the hard palate.

The maxillary complex
• Lateral growth in the mid-face
occurs by displacement apart of
the 2 halves of the maxilla,
with deposition of bone at the midline
suture.
• Maxillary growth ceases at ;
- 15 yrs (girls) &
- 17 yrs (boys).

• The basal bone or the body of
themandible forms one unit, to
which is attached
(1) the alveolar process,
(2) the coronoid process,
(3) the condylar process,
(4) the angular process,
(5) the ramus,
(6) the lingual tuberosity &
(7) the chin

• The ramus moves progressively
posterior by: a combination of
deposition & resorption
• Resorption occurs on the anterior part
of the ramus while bone deposition
occurs on the posterior region
• This results in a ‘drift’ of the ramus in
a posterior direction
Ramus

• The functions of remodeling of the ramus
are:
1. To accommodate the increasing mass of
masticatory muscles inserted into it
2. To accommodate the enlarged breadth of
the pharyngeal space
3. To facilitate the lengthening of the
mandibular body, which in turn
accommodates the erupting molars
Ramus

• Alveolar process develops in response
to the presence of tooth buds
• As the teeth erupt the alveolar process
develops & increases in height by bone
deposition at the margins
• In case of absence of teeth, the
alveolar bone fails to develop & it
resorbs in the event of tooth extraction
The alveolar process

• The chin is a specific human
characteristic & is found in its fully
developed form in recent man only
• In infancy, the chin is usually
underdeveloped
• As the age advances the growth of chin
becomes significant
The chin

• Usually males are seen to have
prominent chins compared to females
The chin

The Mandible
• Growth of the condylar cartilage
elongates the mandible.
• Most mandibular growth occurs as
a result of periosteal activity which
maintains the shape.
Growth ceases at 17 yrs in girls and 19 yrs in boys.

Overall facial growth
1. Head occupies 30% of the body
length & 12% in adulthood
2.The face occupies less than
30% of the skull height &
60% in adulthood, this
demonstrate how rapidly the
brain grows immediately
after birth
3.The brain is fully grown at age
8 years on average

Postnatal growth of the skull and jaws _ Dr. Nabil Al-Zubair

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