BDS [Orthodontics] course

1. Post Natal Growth And Development
PROF (Dr.) SAIBEL FARISHTA

2. There are many treatment modalities that can be initiated during the
growing age.
Post Natal Growth Of The Cranial Base
The maxilla is attached to the cranial base by means of a number of
sutures. The mandible is also attached to the cranial base at the TMJ.
Thus growth processes occuring at the cranial base can affect the
placement of maxilla and mandible.
The cranial base grows post-natally by – cortical drift and remodelling,
elongation at synchondroses and by sutural growth.
Remodeling And Cortical Drift
Remodeling refers to a process where bone deposition and resorption
occurs so as to bring about change in size, shape and relationship of the
bone. The cranium is divided into a number of compartments by bony
elevations and ridges present in the cranial base. These elevated ridges
and bony partitions show bone deposition, while the predominant part of
the floor shows bone resorption. This intracranial bone resorption helps
in increasing the intracranial space to accommodate the growing brain.

3. The cranial base is perforated by the passage of a number of blood
vessels and nerves communicating with the brain. The foramina that
allows these nerves and blood vessels undergo drifting by bone
deposition and resorption so as to constantly maintain their relationship
with the growing brain.

4. Most of the bones of the cranial base are formed by a cartilagenous
process. Later the cartilage is replaced by bone. Certain bands of
cartilage remain at the junction of various bones, these areas are called
Synchondroses. These are primary cartilages and important growth sites
of the cranial base. Important Synchondroses found in the cranial base
are – Spheno-occipital, Spheno-ethmoidal, Inter-sphenoid and
Intra-occipital synchondrosis.
Elongation At The Synchondrosis
• Spheno-occipital Synchondrosis – It is the cartilaginous junction
between the sphenoid and the occipital bones. It is believed to be the
most important and principal growth cartilage of the cranial base during
childhood. It is believed to be active upto 12-15 years of age. At 20 years
of age, the sphenoid and occipital segments then fuse in the midline.
It provides a pressure or compression adapted bone growth, in contrast
to tension adapted growth seen in sutures. This is because the cranial
base supports the weight of the brain and face which bears down on the
synchondrosis in the midline of the vranial base. As endochondral bone
growth occurs at the spheno-occipital synchondrosis, the sphenoid and
occipital bones are moved apart.

5. At the same time new endochondral bone is laid down in the medullary
region and cortical bone is formed in the endosteal and periosteal
regions. Thus the sphenoid and occipital bones increase in length and
width.
The direction of growth of the spheno occipital synchondrosis is upwards.
It therefore carries the anterior part of the cranium bodily forwards. The
growth at the synchondrosis continues till the obliteration of the same by
formation of bone.
Closure of the synchondrosis occurs at around 13-15 years of age.

6. • Spheno-ethmoid Synchondrosis – This is a cartilaginous band between
the sphenoid and ethmoid bone. It ossifies by 5-25 years of age.
• Inter-sphenoidal Synchondrosis – It is a cartilaginous band between the
2 parts of the sphenoid bone. It is believed to ossify at birth.
• Intra-Occipital Synchondrosis – This ossifies by 3-5 years of age.

7. Sutural Growth
The cranial base has a number of bones that are joined to one another
by means of sutures. Some of the sutures that are present are – Spheno-
frontal, Fronto-temporal, Spheno-ethmoid, Fronto-ethmoid and Fronto-
zygomatic.
As the brain enlarges during growth, bone formation occurs at the ends
of the bone.
Timing Of Cranial Base Growth
• By Birth, 55-60% of adult size
• By 4-7 years, 94% of adult size
• By 8-13 years, 98% of adult size

8. Post Natal Growth Of Maxilla
The growth of the naso-maxillary complex is produced by the following
mechanisms – displacement, growth at sutures and surface remodeling.
• Displacement – Maxilla is attached to the cranial base by means of
a number sutures. Thus the growth of the cranial base has a direct
bearing on the naso-maxillary growth.
A passive or secondary displacement of the naso-maxillary complex
occurs in a downward and forward direction as the cranial base
grows. The passive displacement of the maxilla is an important
growth mechanism during the primary dentiton years but becomes
less important as growth of cranial base slows.
A primary type of displacement is also seen in a forward direction.
This occurs by growth of the maxillary tuberosity in a posterior
direction. This results in the whole maxilla being carried anteriorly.
The amount of this forward displacement equals the amount of
posterior lengthening.

10. • Growth At Sutures – The maxilla is connected to the cranium and
cranial base by a number of sutures, these are – Fronto-nasal,
Fronto-maxillary, Zygomatico-temporal, Zygomatico-maxillary and
Pterygo-palatine.
These sutures are all oblique and more or less are parallel to each
other. This allows the downward and forward repositioning of the
maxilla as growth occurs at these sutures. As growth of the
surrounding soft tissue occurs, the maxilla is carried downwards and
forwards. This leads to opening up of space at the sutural
attachments. New bone is now formed on either side of the suture.
Thus the overall size of the bones on either side increases. Hence a
tension related bone formation occurs at the sutures.

11. The following bone remodeling changes are seen in naso-maxillary
complex –
[i] Resorption occurs on the lateral surface of the orbital rim leading to
lateral movement of the eye-ball. To compensate, there is bone
deposition on the medial rim of the orbit and external surface of the
lateral rim.
[ii] The floor of the orbit faces superiorly, laterally and anteriorly. Surface
deposition occurs here and results in growth in a superior, lateral and
anterior direction.
[iii] Bone deposition occurs along the posterior margin of the maxillary
tuberosity. This causes lengthening of the dental arch and enlargement
of the antero-posterior dimension of the entire maxillary body. This helps
to accommodate the erupting molars.
• Surface Remodeling – Massive remodeling of bone occurs by bone
deposition and resorption, which increases the bone size, shape and its
functional relationship.

12. [iv] Bone resorption occurs on the lateral wall of the nose leading to an
increase in size of the nasal cavity.
[v] Bone resorption is seen on the floor of the nasal cavity. To
compensate, there is bone deposition on the palatal side. Thus s
downward shift occurs leading to increase in maxillary height.
[vi] The zygomatic bone moves in a posterior direction. This is achieved
by resorption on the anterior surface and deposition on the posterior
surface.
[vii] The face enlarges in width by bone formation on the lateral surface
of the zygomatic arch and resorption on its medial surface.
[viii] The ANS prominence increases due to bone deposition.
[ix] As the teeth start erupting, bone deposition occurs at the alveolar
margins. This increases the maxillary height and depth of the palate.
[x] The entire wall of the sinus, except the mesial wall undergoes
resorption. This results in increase in size of the maxillary antrum.

14. Post Natal Growth Of Mandible
Of the facial bones, the mandible undergoes the largest amount of
post natal growth and also exhibits the largest variability in
morphology. While the mandible appears in the adult as a single
bone, it is developmentally and functionally divisible into several
skeletal sub-units. The basal bone or the body of the mandible forms
one unit, to which is attached the alveolar process, the coronoid
process, the condylar process, the angular process, ramus, lingual
tuberosity and the chin.
Ramus
The ramus moves progressively posteriorly by combination of
deposition and resorption. Resorption occurs on the anterior part and
deposition on the posterior region. This results in a drift of the ramus
posteriorly. The functions of remodeling of the ramus are: to
accommodate the increasing mass of masticatory muscles inserted
into it, to accommodate the enlarged breadth of the pharyngeal
space and to facilitate the lengthening of the mandibular body, which
in turn accomodates the erupting molars.

15. Corpus or Body Of Mandible
The anterior border of the adult ramus exhibits bone resorption,
while the posterior border shows bone deposition. The displacement
of the ramus results in the conversion of former ramal bone into the
posterior part of the body of mandible. In this manner the body of
the mandible lendthens. Thus additional space made available by
means of resorption of the anterior border of the ramus is made use
of to accommodate the erupting permanent molars.
Angle of The Mandible
On the lingual side of the angle of mandible - resorption takes place
on the posterio-inferior aspect, while deposition occurs on the
antero-superior aspect. On the buccal side, resorption occurs on the
anterio-superior part, while deposition takes place on the postero-
superior part. This results in flaring of the angle of the mandible as
age advances.

17. The Lingual Tuberosity
The lingual tuberosity is a direct equivalent of the maxillary tuberosity,
which forms a major site of growth for the lower bony arch. It forms
the boundary between the ramus and the body. The lingual tuberosity
moves posteriorly by deposition on it’s posteriorly facing surface. The
lingual tuberosity protrudes in a lingual direction lies well towards the
midline of the ramus. The prominence of the tuberosity is increased by
the presence of a large resorption field just below it. This resorption
field produces a depression, the lingual fossa. The combination of
resorption in the fossa and depositionon the medial surface of the
tuberosity itself accentuates the prominence of the lingual tuberosity.
The Alveolar Process
Alveolar process develops in response to the presence of tooth buds.
As the teeth erupt the alveolar process develops and increases in
height by bone deposition at the margins. The alveolar bone adds to
the height and thickness of the body of the mandible and is
manifested as a ledge extending lingual to the ramus to accommodate
the 3rd molars. In case of absence of teeth, the alveolar bone fails to
develop and it resorbs in the event of tooth extraction.

19. The Chin
In infancy, the chin is usually under developed. As age advances the
chin growth becomes significant. It is influenced by sexual and specific
genetic factors. Usually males have prominent chin. The mental
protuberance forms by bone deposition during childhood. Its
prominence is accentuated by bone resorption that occurs in the
alveolar region above it. The deepest point in this concavity is known
as Point B.
The Condyle
The condyle is an important growth site. The condylar head is covered
by a thin layer of cartilage called the condylar cartilage. The presence
of condylar cartilage covering the condyle is an adaptation to
withstand the compression that occurs at the joint. There are two
schools of thought regarding the role of the condyle –
• It was earlier believed that growth occurs at the surface of the
condylar cartilage by means of bone deposition. Thus the condyle
grows towards the cranial base. As the condyle pushes against the
cranial base, the entire mandible gets displaced forwards and
downwards.

20. • It is now believed that the growth of soft tissues including the
muscles and connective tissues carries the mandible forwards away
from the cranial base. Bone growth follows secondarily at the condyle
to maintain constant contact with cranial base.
The condylar growth rate increases at puberty reaching a peak
between 12.5 – 14 years. The growth ceases around 20 years.

21. The Coronoid Process
The growth of the coronoid process follows the enlarging ‘V’ principle.
Viewing the longitidanal section posteriorly - deposition occurs on the
lingual [medial] surfaces of the left and right coronoid process.
Although additions take place on the lingual side, the vertical
dimension of the coronoid process also increases. It follows the ‘V’
principle.
From the occlusal aspect, the deposition on the lingual of the coronoid
process brings about a posterior growth movement in the ‘V’ patern.
Briefly, the coronoid process has a propeller like twist, so that its
lingual side faces three general directions all at once – posteriorly,
superiorly and medially.

22. THANK YOU