Dynamics of growth /certified fixed orthodontic courses by Indian dental academy

DYNAMICS OF
GROWTH
.

www.indiandentalacademy.com

INDIAN DENTAL ACADEMY
Leader in continuing dental education


An in new depth understanding of facial morphogenesis is

essential so that clinician can grasp.
a)
Differences between normal and range of
abnormal.
b)
Biologic reasons for these variations and
differences.
c)
Reasons for rationales utilized in diagnosis,
treatment planning and selection of appropriate clinical
process.
d)
Biologic reasons underlying the problems of
retention, rebound and relapse after treatment.

Concepts to be discussed in dynamics of growth
are:-

Pattern of growth

-

Variability

-

Timing

-

Differential growth

-

Remodeling

-

Drift

-

Displacement

-

Relocation

-

Basicranial flexure

-

Growth field boundaries

Pattern:
In general sense, the pattern reflects
proportionality. Pattern in growth represents
not just a set of proportional relationship at
a point in a time, but the change in these
proportional relationships over time. Pattern
of growth refers to the changes in these
spatial proportions over time.

The facial growth pattern also shows the
cephalocaudal gradient. Mandible being further
away from the brain, tend to grow more and later
than the maxilla, which is closer.
An important aspect of pattern is predictability.
The proportional relationship within a pattern can be
specified mathematically. A change in growth
pattern would indicate an alteration in the expected
and predictable sequence of changes in proportions
expected for that individual.

VARIABILITY:
-

Variability is the law of nature. Because of
infinite number of genetic possibilities, no to
individuals are ever exactly alike.

Variations in response to environment cause
increasing difference among similar individuals with
time. Variability may be demonstrated in many
ways. In physical growth, variability is
demonstrated by the use of statistics, which express
quantitatively the range of differences found in a
large population of individuals of similar age, sex,
socioeconomic background and race

It can be difficult, but clinically very important to

decide weather an individual is merely at the
extreme of the normal variation of changes in
proportions expected for that individual.
Rather than categorizing people as normal or
abnormal, it is more useful to think in terms of
deviations from the usual pattern and to express
variability quantitatively. One way to do this is to
evaluate a given child relative to peers on a
standard growth chart.

TIMING:
-

A final major concept in physical growth
and development is timing.

Variation in growth and development
because of timing are particularly evident in
human adolescence. Some children grow rapidly
and mature early, completing their growth
quickly and thereby appearing on the high side
of developmental charts until their growth
ceases and their contemporaries begin to catchwww.indiandentalacademy.com
up.

Differential Growth
-

The human body does not grow at some rate
throughout the life. Different organs grow at
different rates to a different amount and at a
different times. This a termed differential growth.
-

The concept of differential growth can be
explained on the basis of scammons curve of
growth

The body tissue can be broadly classified into
four types i.e.
Lymphoid tissue
Neural tissue
General tissue
Genital tissue
-

Each of these grow at different times and
different rates.

A bone

does not grow by generalized, uniform
deposition of new bone (+) on all outside
surfaces, with corresponding resorption (-) from
all inside surfaces. Because of the
topographically complex nature of each bone's
shape, the bone must have a differential mode
of enlargement, in which some of its parts and
areas grow much faster and to a much greater
extent than others

Two basic kinds of growth movement occur during the
enlargement of each bone in the facial and cranial
skeleton: (1) remodeling, which produces the size,
shape, and fitting of a bone, and (2) displacement.
Displacement is a movement of whole bones away from
one another, creating the space within which growth
enlargement of each of the separate bones takes place.
Cortical drift is the process that carries out the
remodeling functions, and it is a direct growth
movement produced by deposition of new bone on one
side of a cortical plate, with resorption from the opposite
side.

THE BONE REMODELING PROCESS
The surface that faces toward the direction of
movement is depository (+). the opposite surface,
facing away from the growth direction, is resorptive (-).
If the rates of deposition and resorption are equal, the
thickness of the cortex remains constant. If deposition
exceeds resorption, overall size and cortical thickness
gradually increase.
Different combination
of
resorption and deposition (drift) in a variety of regional
directions and amounts throughout the entire bone
provide for the remodeling enlargement of the bone as
a whole.

DIFFERENTIAL GROWTH


CORTICAL DRIFT


RELOCATION


V PRINCIPLE AND REMODELING
PATTERN


DISPLACEMENT


SECONDARY DISPLACEMENT


POST NATAL GROWTH OF
MAXILLA


POST NATAL GROWTH OF
MANDIBLE


BRAIN ENLARGEMENT, BASICRANIAL
FLEXURE, AND FACIAL ROTATIONS
The enormous human cerebrum similarly
expands around a much smaller enlarging
midventral segment (the medulla, pons,
hypothalamus, optic chiasma).This causes a
bending of the whole underside of the brain. The
flexure of the cranial base results. The foramen
magnum in the typical mammalian skull is
located at the posterior aspect of the cranium. In
man, it is in the midventral part of the expanded
cranial floor at an approximate balance point for
upright head support on a vertical spine.

The expansion of the frontal lobes displaces the frontal
bone upward and outward. This results in the distinctive,
bulbous, upright "forehead" of the human face, although it is
really part of the neurocranium and not the face proper. The
frontal lobes also relate to a rotation of the human orbits into
new positions. As the forehead is rotated into a vertical plane
by the brain behind it, the superior orbital rim is carried with
it. The eyes now point at a right angle to the spinal cord. The
spine is vertical, and the orbital axis is horizontal. Vision is
directed toward forward body movement.

The expansion of the frontal and,
particularly, the temporal lobes of the
cerebrum relates to a rotation of the orbits
towards the midline and the eyes come
closer together. The enlarged human
cerebrum has caused a downward rotational
displacement of the olfactory bulbs. the
olfactory bulbs relate directly to the
alignment and the direction of growth of the
adjacent nasal region. The plane of the
nasomaxillary region is thereby
approximatelywww.indiandentalacademy.com to the plane
perpendicular
of the olfactory bulbs.

As the bulbs become rotated
progressively from a vertical position to
horizontal one because of increase in brain
size or because of its shape, the whole face
is similarly rotated from a horizontal to a
vertical plane. Or, stated another way, the
face is rotated down by the expanded
anterior cranial floor as it rotates downward
as a result of the enlargement of the frontal
lobes.
.


NASOMAXILLARY CONFIGURATION
The maxilla of most mammals has a triangular
configuration .In man, it is uniquely rectangular. This is
caused by a rotation of the occlusion into a horizontal
plane to adapt to the vertical rotation of the whole
midface. In the human maxilla, the design change that
allows for this resulted in the creation of a new archpositioning facial region, the suborbital compartment.
Most of this phylogenetically expanded area is occupied
by the otherwise nonfucntional maxillary sinus (uses
such as air warming, nasal drip, and voice resonance are
secondary. An orbital floor was also newly created in
conjunction with this added facial region.

The characteristic vertical human facial profile is a
composite result of (1) a bulbous forehead, (2)
rotation of the nasal region into a vertical plane, (3)
reduction of snout protrusion in conjunction with
medial orbital convergence, (4) rotation of the orbits
into upright positions, (5) rotation of the maxillary
arch downward and backward, and (6) bimaxillary
reduction


Reduction of the nasal region associated with orbital
convergence and olfactory-anterior cranial fossa
rotation must necessarily also be accompanied by a
more or less equal reduction in maxillary arch length,
because the floor of the nasal chamber is also the roof
of the mouth. The protrusion of the cartilaginous and
soft tissue portion of the nasal complex provides for
downward-directed external nares. This aims the
inflow of air obliquely upward into the vertically
disposed nasal chambers towards the vertically
aligned sensory nerves of the olfactory bulbs located
on the ceiling of the chambers.

GROWTH FIELD BOUNDARIES
The growth of each of the face involves two
basic considerations. The first is the amount of
growth, and the second is the direction of growth.
These two factors constitute the growth "vector."
The floor of the cranium, in turn, is the template
upon which the face is built. The junctional part of
the face cannot be significantly wider, for
example, than the maximal width of the cranium
The length of specific parts of the cranial floor are
expressed as equivalent dimensions for the face.

The forward boundary of the brain is shared
by the forward border of the nasomaxillary
complex. The direction of growth by the nasal
part of the face is established by the olfactory
bulbs and the sensory olfactory nerves. These
two factors underlie the "vector" of midfacial
growth, that is, the amount and the direction.
The nasomaxillary complex grows as far
forward as the edge of the brain in a direction
approximately perpendicular to the olfactory
bulbs.

The posterior boundary of this fossa
establishes the corresponding posterior boundary for
the midface. This is essentially a nonvariable
anatomic relationship. The direction of growth in
this region is established by the particular special
sense located in this part of the face, which is the
visual sense. the posterior plane of the midface
extends from the junction between the anterior and
middle cranial fossae (and the inferior junction
between the frontal and temporal lobes) downward in
a direction perpendicular to the neutral line of the
orbit. This plane passes almost exactly along the
posterior surface of the maxillary tuberosity.

The inferior boundary of the nasomaxillary
complex is established by the bottom-most
surface of the brain and cranial. A line from
the floor of the posterior cranial fossa passes
through , or very nearly so, both the inferior
corner of the posterior maxillary tuberosity
and the inferior corner of the front part of the
bony maxillary arch (prosthion). This
relationship is achieved only after facial
development is complete, because neurocranial
growth precedes facial growth.

Any variation in the alignment of the nerve
is usually accompanied by a corresponding
upward or downward rotational alignment
of the palate. In its neutral position. If the
palate has undergone a severe clockwise or
counterclockwise rotation during
development, the palatal plane will project
well above or below, respectively, the
occipital point.

The growth in each region of the face involves two
basic factors: (1) the amount of growth by any given
part and (2) the direction of growth by that part. The
brain establishes (or at lest shares) the various
boundaries that determine the amount of facial growth.
this is because the floor of the cranium is the template
upon which the face is constructed. The directions of
regional growth among the different parts of the face
are inseparably associated with the special sense organs
housed within the face. These two factors establish a
prescribed growth perimeter that defines the borders of
the growth compartment occupied by the nasomaxillary
complex

CONCLUSION
The conventional method used to
show facial growth is superimposition of
serial head film tracings. Sella is usually
used as a registration point for the
superimposition.
Superimposing on the cranial base
demonstrates the downward and forward
expansion of the whole face relative to
cranial base.

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Dynamics of growth /certified fixed orthodontic courses by Indian dental academy

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