Orthodontics- growth and development

1. GROWTH AND
DEVELOPMENT

3. • Growth can be defined as an increase in
size or number.
• Development can be defined as an
increase in complexity.
• Growth is largely an anatomic
phenomenon whereas development is
physiological and behavioral.

5. Patterns Of Growth
• Pattern of growth refers to changes in proportions over
time.
• Example All the tissues of the body do not grow at
the same rate.Scammons curve for growth for the
four major tissue systems of the body shows that
growth of the neural tissues is nearly complete by 6
or 7 years of age. General body tissue including
muscle bone and viscera show an s shaped curve
with a definite slowing of the rate of growth during
childhood and acceleration at puberty. Lymphoid
tissues proliferate far beyond the adult amount in
late childhood, and then undergo involution at the
same time that growths of the genital tissues
accelerate rapidly.

6. Timing of Growth
• Timing in growth refers to the fact that the same
event happens for different individuals at
different times or in other words the biologic
clocks of different individuals are set differently.
• In human adolescence, some children grow
rapidly and mature early, completing their growth
quickly and thereby appearing on the high side
of development charts until their growth ceases
and their contemporaries begin to catch up.

7. METHODS OF STUDYING
PHYSICAL GROWTH

8. Craniometry
• This was the first of the
measurement
approaches for studying
growth based on
measurements of human
skulls. It has the
advantage that rather
precise measurements
can be made on dry
skulls and has the
important disadvantage
that it provides cross
sectional data which is
not supportive for growth
studies.

9. Anthropometry
In this technique, various
landmarks established in
studies of dry skulls are
measured in living individuals’
simply by using soft tissue
points overlying these bony
landmarks. Although the soft
tissue introduces variation,
anthropometry does make it
possible to follow the growth of
an individual directly, making
the same measurements
repeatedly at different times.
This produces longitudinal
data which is advantageous for
growth studies.

10. Cephalometric Radiology
• This method is not only important
in the study of growth, but also in
the clinical evaluation of
orthodontic patients. This
technique allows a direct
measurement of bony skeletal
dimensions, since the bone can be
seen through the soft tissue
covering in a radiograph, but it
also allows the same individual to
be followed over time. Growth
studies are done by
superimposing a tracing or digital
model of a later cephalogram on
an earlier one, so that the changes
can be measured. The
disadvantage of this technique is
that it produces a two dimensional
image of a three dimensional
structure therefore all
measurements are not possible.

11. 3 D Imaging
• CT allows the 3D constructions of
the cranium and face, to plan
surgical treatment for patients with
facial deformities. CBCT has been
applied to facial scans reducing
the amount of radiation dose and
allowing scans of patients with
radiation dose much closer to hat
of cephalograms. MRI also
provides 3D images that can be
used in studies of growth, with the
advantage that there is no
radiation exposure with this
technique. This method has
already been applied to analysis of
growth changes produced by
functional appliances.

12. Vital staining
• This is a technique in which dyes that stain mineralized
tissues are injected into an animal. These dyes remain in
the bones and teeth of the animal and can be detected
later by the sacrifice of the animal. A dye called alizarin
which is still is used for vital staining studies reacts
strongly with where bone calcification is occurring. Since
these are the sites of active skeletal growth, the dye
marks the location at which active growth was occurring
when it was injected. These studies are not possible in
human beings. Tetracycline a drug used to treat
infections is an excellent vital stain that binds to calcium
at growth sites in the same way as alizarin. With the
development of radioactive tracers, it has been possible
to use any almost any radioactively labeled metabolite
that can be incorporated in tissues as a vital stain. The
gamma emitting isotope Tc99 can be used to detect
areas of rapid bone growth in humans.

13. Implant Radiography
• In this technique applicable to
studies of human beings, inert
metal pins are placed in bones
anywhere in the skeleton,
including the face and the jaws. If
metallic implants are placed in the
jaws, a considerable increase in
the accuracy of a longitudinal
cephalometric analysis of growth
pattern can be achieved.
Superimposing cephalometric
radiographs on the implanted pins
allows precise observation of both
changes in the position of one
bone to another and changes in
the external contours of individual
bones.

14. THEORIES OF GROWTH
CONTROL

15. Growth site and growth centre
• Three major theories have attempted to explain
the determinants of craniofacial growth.
• The first one is based upon bone as the primary
determinant, second on the cartilage while the
third one is based upon soft tissue matrices.
• Growth Site is a location at which growth occurs
• Growth Centre is a location at which
independent (genetically controlled) growth
occurs.

16. Growth Centre
Growth Centre- site of endochondral
ossification with tissue-separating force
(genetically controlled) growth occurs. ,
contributing to the increase of skeletal
mass.
i.e. location at which independent growth
occurs

17. Growth Site
Growth site: regions of periosteal or sutural
bone formation and modeling resorption
adaptive to environmental influences.
i.e. merely location at which growth occurs.

18. Sutural Dominance Theory
• SICHER – studies using vital dyes – sutures
caused much of growth
• “….the primary event in sutural growth is the
proliferation of the connective tissue between
the two bones. If the sutural connective tissue
proliferates it creates the space for oppositional
growth at the borders of the two bones.”
• Connective tissue in sutures of nasomaxillary
complex & vault – separated bones like
synchondrosis & epiphyseal plate

21. • 2 differing views concerning the structure of the
sutures –
1. Three-layer structure:
- Connective tissue
between the two bones - same as cartilage at
the base of the skull, epiphyses, and articular
surfaces of long bones
- "spreading" of the suture, initiated by the
proliferation of the middle layer cells of the
sutural tissue.
-"tissue-separating force" in the
sutural tissue.

22. 2. Five-layer structure :
-Each bone at the suture has
its own two-layer periosteum covering +
opposing surfaces of the bones
-fifth layer between these periosteal layers
- allows for slight adjustments between the
bones during growth -active proliferating
role - layers of the periosteums of each
bone.

23. Evidence against Sutural
dominance theory
1. Subcutaneous auto transplants of the
zygomaticomaxillary suture area in the guinea pig have
not been found to grow – lack of innate growth
potential.
2. Growth of sutures – respond to external stimuli.
3. Extirpation of facial sutures - no appreciable effect on
growth of the skeleton.
4. Shape of sutures - depends on functional stimuli
5. Closure of sutures -extrinsically determined.
6. Sites of sutures - not predetermined .

24. CONCLUSION:
• Sutures are growth sites not centres.
• Adaptive, compensatory or secondary
growth occurs in these sutures.

25. Cartilaginous theory
SCOTT’S HYPOTHESIS:
• Intrinsic growth-controlling factors in cartilage &
periosteum.
• Sutures are secondary & dependent on
extrasutural influences.
• Cartilaginous part of skull must be recognised as
primary centres of growth, with nasal septum
being a major contributor in maxillary growth, per
se.
• Sutural growth – responsive to synchondrosis
proliferation & local environmental factors.

26. Cranial Base Synchondroses

27. • Removal of spheno-occipital
synchondrosis - results in an arrest of
growth in length of the cranial base .
• Pressure & tension – little effect on
cartilage.
• Intramembranous bone- immediate
response.

29. • Endochondral cranial base – lesser
response to brain growth than
intramembranous cranial vault.
• Primary centres of growth – Sarnat, Burdi,
Baume, Petrovic & others.

30. • Endochondral ossification at the synchondroses-
only a response to external stimuli?
• Cartilage- lacks same amount of independent
growth potential as transplants of epiphyseal
cartilage under similar experimental conditions.
• Spheno-occipital synchondrosis appears to
close much earlier than is usually stated in the
textbooks -11 to 16 years of age

31. Nasal septal cartilage
• Scott- primary cartilage in nasal septum –
primary mechanism for growth of nasomaxillary
complex.
• Latham- ligament extending from nasal septal
cartilage to to anterior premaxillary region –
SEPTOPREMAXILLARY LIGAMENT.
• This is an important relation between midfacial
& nasal septal growth – especially before birth.

33. • Histologic examination - endochondral
ossification at the septo-ethmoidal junction
and area of proliferation at the vomeral
edge of the cartilage
• In the palatal area - resorption on the
nasal side and apposition on the oral side
of the bony palate.

34. Condylar cartilage

35. • Growth of the condylar cartilage is responsible for the
anteroposterior growth of the mandible- primary growth
centre.
• Scott- growth of the condylar cartilage enables the
condyle "to grow upwards and backwards so as to
maintain the contact at the temporomandibular joint as
the mandible is carried downwards and forwards by the
growth of the upper facial skeleton."
• If the condylar cartilage is transplanted to a relatively
nonfunctional site, such as the subcutaneous or brain
tissue, it does not maintain its structure and does not
behave like the condylar cartilage in situ.
• Bilateral condylectomy, congenital absence of the rami-
no appreciable effect on the growth of the rest of the
mandible in humans.

36. Functional Matrix Theory
• According to this theory the control growth lies within the
adjacent soft tissues.
• This theory was put forward by Moss in 1960.
• This theory holds that neither the cartilage of the
mandibular condyle nor the nasal septum is a
determinant of jaw growth. Instead the growth of the face
occurs as a response to functional needs and is
mediated by the soft tissue in which the jaws are
embedded i.e. the soft tissue grows and both bone and
cartilage react.
• Growth of the cranial vault is a direct response to the
growth of the brain. Pressure exerted by the brain
separates the cranial bones at the sutures, and new
bone passively fills in at these sites so that the brain
case fits the brain. cranium is also very small, and the
condition of microcephaly

37. • In hydrocephalus, the absorption of CSF is impeded,
fluid accumulates and intracranial pressure builds up.
This pressure does not allow the brain to grow and these
patients have small brains but this condition leads to an
enormous skull.
• Other example is the relationship between the eye and
the orbit. An enlarged eye will cause a corresponding
change in the size of the orbital cavity and the eye acts
as functional matrix.
• According to Moss, the major determinant of growth of
the maxilla and mandible is the enlargement of the oral
and nasal cavities which grow in response to functional
needs.

38. • In summary, it appears that growth of the cranium
occurs almost entirely in response to growth of the brain.
Growth of the cranial base is primarily the result of
endochondral growth and bony replacement at the
synchondroses, which have independent growth
potential but perhaps are influenced by growth of the
brain. Growth of the maxilla occurs from a combination
of growth at sutures and direct remodeling of the
surfaces of bone. The maxilla is translated downwards
and forwards as the face grows, and new bone fills at the
sutures. Growth of the mandible occurs by
endochondral proliferation at the condyle and apposition
and resorption of bone at its surfaces. It seems clear that
that the mandible is translated in space, by the growth of
the muscles and other adjacent soft tissue structures,
and that addition of new bone at the condyle is in
response to the soft changes.