GROWTH OF MAXILLA
• The study of head form in man has always been of
considerable interest to anthropologist, anatomists, & other
students of human growth. In fact, the wide array of
students involved in solving the complex phenomenon of
“GROWTH “have been aptly described by Krogman as early
as 1943 in these golden words:“ Growth was conceived by an
anatomist ,born to a biologist ,delivered by a phisician,left
on a chemist’s doorstep & adopted by a physiologist.At an
early age she eloped with a statistician, divorced him for a
psychologist & is now being wooed , alternately &
concurrently by an endocrinologist,a pediatrician , a
physical anthropologist, an educationalist , a biochemist , a
physicist , a mathematician , an orthodontist , a eugenicist &
the children’s bureau”.
According to “ TODD”
“Growth is an increase in size &
,Development is progress towards
maturity
Some definitions related to
Growth
As is the nature of growth where in the concepts keep
changing with new research findings there has been no
single definitions associated with it:
Different researchers have defined growth in various ways.
- The self multiplication of living substance – JX Huxely.
- Increase in size, change in proportion & progressive
complexity.- Krogman
-Entire series of sequential anatomic & physiological changes
taking place from the beginning of prenatal life to senility
–Meredith.
-Quantitative aspect of biologic development per unit of
time-Mayers
-Change in any morphological parameter, which is measurableMoss.
i
Terminology Related To Growth:
Growth Fields :
The outside & inside surfaces of a bone are
blanketed by a mosaic-like, pattern of soft tissues,cartilage
or osteogenic membrane called as Growth Fields.
There when altered are capable of producing an alteration
in the growth of the particular bone.
Growth Sites :
Growth sites are growth fields that have a
special significance in the growth of a particular bone.
Eg. Mandibular condyle in the mandible,
Maxillary tuberosity in the maxilla.
The growth sites may process some intrinsic potential to
growth.
Remodeling :
It is the differential growth activity involving
simultaneous deposition & resorption on all the inner & outer
surfaces of the bone.
Eg. Ramus moves posteriorly by a combination of resorption &
deposition.
Growth Centers:
Growth centers are special growth
sites , which control the overall growth of the bone.
Eg. Epiphyseal plates of long bone.
Mechanism Of Bone Growth
• Bone is a specialized tissue of mesodermal origin.It
forms the structural framework of the body.
• Bone is calcified tissue that supports the body &
gives points of attachment to the musculature.
• Normal bone contains between 32-36% of organic
matter.
-Bone deposition & deposition
-Cortical drift
-Displacement
Bone deposition & resorption:
Bone changes in shape & size by two basic
mechanisms,bone deposition & bone resorption.The
bone deposition & resorption together is called “
BONE REMODELING”.
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 of the bone with adjacent
structures.
Cortical Drift:
- Most bones grow by interplay of bone deposition &
resorption .
- A combination of bone deposition & resorption
resulting in a growth movement towards the
deposition surface is called “Cortical Drift”.
- If bone deposition & resorption on either side of a
bone are equal the thickness of the bone
remains constant.
- If in case more bone is deposited on one side & less
bone resorbed on the opposite side – The
thickness of the bone increases.
Displacement:
• It is the movement of the whole bone as a unit.
• Displacement can be of two types.
Primary displacement:
If a bone gets displaced as a result of its own
growth,it is called “Primary displacement”.
eg. Growth of the maxilla at the tuberosity region results in
pushing of the maxilla against the cranial base which results in
pushing of the maxilla against the cranial base which results in
the displacement of the maxilla in a forward & downward
direction.
Secondary displacement:
If the bone gets displaced as a result of
growth & enlargement of an adjacent bone, it is called
Secondary displacement.
eg. The growth of the cranial base causes the forward &
downward displacement of the maxilla.
Characteristics of Bone
Growth
Bone formation occurs by 2 methods of differentiation of mesenchymal
tissues that may be of mesodermal or ectomesenchymal origin.
Accordingly 2 types of bone growth is normally seen.
1)
.
Intra-membranous ossification :
The transformation of mesenchymal connective tissue
usually in membranous sheets,into osseous tissues.
Endochondral ossification:
The conversion of hyaline cartilage prototype models
into bone.
The interstitial growth expansion capability of cartilage, even
under weight pressure due to its avascularity precluding
ischemia,(Cartilage nutrition is provited by perfusing tissue
fluids that are not easily obstructed by load pressures) allows
for directed prototype cartilage growth. The cartilage
‘template ‘ is then replaced by endochondral bone accounting for
indirect bone growth.
Growth and development of an individual can be divided into
PRENATAL & the POSTNATAL periods. The pre-natal
period of development is a dynamic phase in the
development of a human being.During this period, the
height increases by almost 5000 times as compared to only
a threefold increase during the post-natal period.The renatal life can be arbitrarily divided into three periods.
1. Period of the Ovum
2. Period of the Embryo
3. Period of the Fetus
1.
Period of the ovum:
This period extends for a period of approximately
two weeks from the time of fertilization. During this period the
cleavage of the ovum and the attachment of the ovum to the
intra-uterine wall occurs.
2.
Period of the embryo:
This period extends from the fourteenth day to
the fifty sixth day of intra-uterine life. During this period the
major part of the development of the facial & the cranial region
occurs.
3.
Period of the fetus:
This phase extends between the fifty sixth day of
intra-uterine life till birth.In this period ,accelerated growth of
the cranio-facial structures occurs resulting in an increase in
their size.In addition, a change in proportion between the various
structures also occurs.
Prenatal Growth Of Maxilla
Around the fourth week of intra-uterine life, a prominent bulge appears on
the ventral aspect of the embryo corresponding to the developing brain.
Below the bulge a shallow depression which corresponds to the primitive
mouth appears called “ STOMODEUM”.
The floor of the stomodeum is formed by the buccopharyngeal membrane
which separates the stomodeum from the foregut.
By around the 4th week of intra-uterine life,
five branchial arches form in the region of the
future head & neck.Each of these arches gives
rise to muscles,connective
tissue,vasculature,skeletal components,& neural
components of the future face.
The first branchial arch is called the mandibular arch & plays an
important role in the development of the naso- maxillary
region.
The mesoderm covering the developing forebrain proliferates &
forms a downward projection that overlaps the upper part of
stomodeum .This downward
projection is called “FRONTO-NASAL PROCESS”.
The stomodeum is thus overlapped superiorly by the fronto-nasal
process. The mandibular arches of both
The sides form the lateral walls of the stomodeum.
The mandibular arch gives off a bud from its dorsal end called the
“MAXILLARY PROCESS”.
The maxillary process grows ventro-medio-cranial to the main
part of the mandibular arch which is now called the
“MANDIBULAR PROCESS”.
Thus at this stage the primitive mouth or stomodeum is
overlapped from above by the frontal process,below by the
mandibular process & on either side by the maxillary process.
The ectoderm overlying the fronto-nasal process shows bilateral
localized thickenings above the stomodeum. These are called
the “NASAL PLACODES”.These placodes soon sink and form
the nasal pits.
The formation of these nasal pits divides the fronto-nasal
process into two parts:
a)The medial nasal process &
b)The lateral nasal process
The two mandibular processes grow medially & fuse to
form the lower lip & lower jaw.
As the maxillary processe become narrow so that the
two nasal pits come closer. The line of fusion of the
maxillary process & the medial nasal process
corresponds to the naso-lacrimal duct.
POST-NATAL GROWTH Of MAXILLA
Since, the maxillary complex is attached to the cranial
base, there is a strong influence of the latter on the
former. Although there is no sharp line of demarcation
between the cranium & maxillary growth gradients,yet
the position of the maxilla is dependent upon the
growth at spheno-occipital & spheno-occipital
synchondroses.Hence, while discussing the growth of
nasomaxillary complex, we have to look into two
aspects.
1)The displacement in the position of the maxillary
complex,
-Secondary displacement- Occurs in a
downward & forward direction as the cranial base
grows.
-Primary displacementoccurs in a forward direction.This
occurs by gowth of the maxillary tuberosity in a
posterior direction .This results in the whole maxilla
being carried anteriorly.
2) Growth at sutures:
.
- Sutural connective tissue,
- Proliferation
- Ossification
- Surface apposition
- Resorption
- Translation are the mechanisms for
maxillary growth.
- Maxilla is related to cranium at least partially by the,
- Frontomaxillary suture
- Zygomaticotemporal suture
- Zygomaticotemporal suture
- Pterygogopalatine suture
These sutures are all oblique & more or les parallel with
each other.The growth in these areas would serve to
move the maxilla downward & forward.
3)Surface Remodeling:
Remodeling occurs by bone deosition &
resorption to bring about:
a) Increase in size
b) Change in shape
c) Change functional relationship
Bone remodeling seen in the midfacial region
Bone remodeling of the palate resulting in its
downward displacement
Growth of the palate exhibiting V pattern of
growth
The naso-maxillary complex as it emerges from
beneath the cranium
Moss Cites three types of bone growth changes
to be observed in the maxilla
1)
Those changes that are associated with compensations
for the passive motions of the bone brought about by
the primary expansions of the orofacial capsule.
2)
There are changes in bone morphology associated with
alterations in the absolute volume, size shape or
spatial position of any or all the several relatively
independent maxillary functional matrices, such as
orbital mass.
3)
There are bone changes associated with the
maintenance of the form of the bone itself.
All these changes do not occur simultaneously but rather
differentially or squentially.