Tooth development 3 /certified fixed orthodontic courses by Indian dental academy

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


‫بسم ا الرحمن‬
‫الرحيم‬
IN THE NAME OF ALLAH THE MOST
GRACIOUS THE MOST MERCIFUL

Niagra Falls


DEVELOPMENT AND
GROWTH OF TEETH
Prof. Abdelhamied Y. Saad, BDS, MS (Egypt), Ph.D. (U.S.A.)


• The stomodeum is lined with ectoderm.
• It is separated from the blind upper end
of the foregut by bucco-pharyngeal
membrane.
• This membrane ruptures at about 27
days.


The ectoderm consists of:
1. A basal layer of columnar cells.
2. A surface layer of flattened cells.


• Most of the C.T. cells underlying the
oral ectoderm are neural crest cells or
ectomesenchyme in origin.


Dental lamina appears after
37 days of development
• It is continuous band of thickened
epithelium in the presumptive upper
and lower jaws.
• It is roughly horse-shoe shaped
structure corresponding to the position
of the future deciduous teeth.

• Each tooth develops from a tooth germ
that forms from the lining of the oral
cavity.


A tooth germ consists of 3 parts:
1. An enamel organ; derived from the oral
ectoderm and produces the enamel.
2. A dental papilla, derived from the
ectomesenchyme and produces dentin and
pulp.
3. A dental sac (tooth follicle); derived from
the ectomesenchyme and produces
cementum, PDL, and alveolar bone.

Developmental Stages
• Bud stage
• Cap stage
• Bell stage


Bud Stage


Cap Stage


E. navel


Function of Enamel Knot
1. It may act as signaling center,
producing a unique set of signaling
molecules for tooth development.


Function of Enamel Knot
2. Acts as an organizing center that
initiates cuspal morphogenesis and
crown pattern formation.


Fate of Enamel Knot
• It undergoes programmed cellular
death (apoptosis) at the onset of the
early bell stage.


Bell Stage
• Early
• Late (advanced)


Early Bell Stage

Morpho-differentiation
Proliferation
Histodifferentiation
Induction
main dental lamina
lateral dental lamina
successional dental lamina
outer dental epithelium
stellate reticulum
inner dental epithelium
cervical loop
Dental papilla


”Dental sac “follicle

Fine Structure of the Enamel
Organ at the Bell Stage
• It is relatively uncomplicated but must
be understood to know the
ultrastructural changes occurring in
the formation of the dental hard tissue,
enamel and dentin.


• The enamel organ is supported by a
basal lamina around its periphery.
• The outer enamel epithelial cells are
cuboidal and have a high nuclear /
cytoplasmic ratio (little cytoplasm).


• Their cytoplasm contains:
(1) free ribosomes,
(2) few endoplasmic reticulum,
(3) some mitochondria, and
(4) a few scattered tonofilaments.
•

Adjacent cells are joined by junctional
complexes.

• The stellate reticulum cells are
connected to each other, to the cells of
the outer enamel epithelium, and to
stratum intermedium by desmosomes.
• Their cytoplasm contains all the usual
cytoplasmic organelles, but these are
sparsely distributed.


• The cells of the stratum intermedium
are connected to each other and to the
cells of the stellate reticulum and inner
enamel epithelium by desmosomes.
• Their cytoplasm also contains the
usual complement of organelles and
tonofilaments.


• The inner enamel epithelial cells have a centrally
placed nucleus and a cytoplasm that contains:
(1) Free ribosomes.
(2) A few scattered rough endoplasmic reticulum.
(3) Mitochondria evenly dispersed.
(4) Some tonofilaments.
(5) A Golgi complex situated towards the stratum
intermedium.
(6) A high glycogen content.

•

Before forming the first dentin, cells
of the enamel organ and, in particular,
those of the inner enamel epithelium
receive
nourishment
from
two
sources:
1. Blood vessels located in the dental
papilla.
2. Vessels situated along the periphery
of the outer enamel epithelium.

• When the dentin is formed, it cuts off
the papillary source of nutrients.
• This occurs at a time when the cells of
the inner enamel epithelium are about
to secrete enamel.


• An apparent collapse of the stellat
reticulum will occur and the
ameloblasts will be approximated to
the blood vessels lying outside the
outer enamel epithelium.


Both dentinogenesis and amelogenesis have begun.
Note collapse of the stellate reticulum & folding of IEE.

•

Until this point the ameloblasts meet
their metabolic requirements by:
1. Using the glycogen stored in their
cytoplasm, and
2. Probably also by using some of the
extracellular components of the
stellat reticulum.


•

Epithelial- ectomesenchymal
inductive interaction during normal
odontogenesis lead to:
1. Cytodifferentiation of dentin and
enamel forming cells, as well as
2. To subsequent dental hard tissue
formation.


•
1.
2.
3.
4.

It has been demonstrated that
extracellular matrix composed of:
Collagen,
Glycoproteins,
Glycosaminoglycans, and
Additional macro-molecules may
represent an important factor in
mediating developmental events of
odontogenesis by inducing an
organizing influence between
epithelial and ectomesenchyme.

Function of the Dental Lamina
1. Initiation of the entire deciduous
dentition.
2. Initiation of the successors of
deciduous dentition.
3. Formation of permanent molars by
distal extension.

Fate of the Dental Lamina
• During the cap stage, the dental lamina
maintains a broad connection with the
enamel organ.


• In the bell stage, it begins to break up
by mesenchymal invasion, which first
penetrates its central portion and
divides it into lateral lamina and the
dental lamina proper.


• The mesenchymal invasion is at first
incomplete and does not perforate the
dental lamina.


(Disintegrated)


• The dental lamina proper (successional
lamina) proliferates only at its deeper
margin, which becomes free and
situated lingually to the enamel organ
and forms the primordium of the
permanent tooth.


• The epithelial connection of the enamel
organ with the oral epithelium is
severed by the proliferating mesoderm.


• Fragmentation of the dental lamina
results in the formation of discrete
cluster of epithelial cells that normally
degenerate and are resorbed.


• If any persist, they may form small
cysts (eruption cysts) over the
developing tooth and delay eruption.


• Remnants of the dental lamina persist
within the jaw and gingiva as epithelial
pearls or islands called epithelial rests
of Serres.


Functions of Enamel Organ
1. It has a morphogenetic function that
helps to determine the crown pattern.
2. It has an inductive role in initiating
coronal and root dentinogenesis and
therefore determines the size, shape,
and number of roots.
3. It has a formative function in that its
cells elaborate enamel.

Functions of Enamel Organ
4. It has a protective function that
prevent exposure of the crown to
surrounding connective tissue before
eruption.
5. It permits tooth eruption.
6. It assists in establishing the
dentogingival junction.

Some investigators prefer the
term dental organ instead of
enamel organ because:
1. It is responsible for determining the
shape of the crown.
2. Initiating dentin formation.
3. Establishing the dentogingival
junction.
4. Forming enamel.

Vestibular Lamina
• Labial and buccal to the dental lamina
another epithelial thickening develops
independently and somewhat later. It
is the vestibular lamina (lip furrow
band).


Main
dental lamina


Vestibular
lamina

• It subsequently hollows and
disappears and forms the oral vestibule
(oral sulcus) between the alveolar
portion of the jaw and the lips and
cheeks.


Root Formation


Multi-rooted Teeth


Epithelial-Mesenchymal
Relations
• In the developing embryo a functional
relationship exists between epithelium
and the mesenchyme that supports it.
• The proper interplay between these
tissues are essential for orderly
development.

Therefore:
1. Teeth cannot form until ectomesenchyme
establishes contact with the epithelium.
2. The shape of the tooth is determined by folding of
the dental epithelium, and this folding is dictated by
the mesenchyme of the dental papilla.
3. Odontoblast differentiation requires the presence of
epithelium.
4. The anatomy of the dentogingival junction
(attachment epithelium) is determined by its
supporting connective tissue.
… and the list goes on.

How Cells And Tissues
Communicate With Each Other
• Communication is possible between cells
through either:
1. Direct cell-to-cell contact.
2. The transmission of molecules (cytokines)
synthesized and secreted by one cell and then
captured by surface receptors of another cells.
These molecules which, once captured, can
influence cell behavior and phenotype.

• When cells come into contact with each
other, junctional arrangements are
established that can take several forms
such as desmosomes, tight junction,
and gap junction.


• Most are concerned with adherence;
but one form of junction, the gap
junction, permits direct communication
between cells which occurs frequently
between embryonic cells of the same
population.


• This suggests that they likely have some role to play
in development.
• No evidence exists, however, for the occurrence of
cell-to-cell contact between epithelial and
ectomesenchymal cells during early stages of tooth
development.
•

Indeed, the presence of a basal lamina (consisting of
two layers; a lamina lucida and a lamina densa)
between the two tissues preclude direct contact.


The main constituents of the
basal lamina are:
• Type IV collagen.
• The adhesive glycoproteins laminin
and fibronectin.
• The proteoglycan heparan sulfate.


• The basal lamina supports and binds
the dental epithelium and in addition,
according to some investigators,
contributes to epithelial-mesenchymal
communication.


It does this in two ways:
1. It acts as a dynamic sieve that can control
the passage of extracellular molecules (or
isolated basal lamina produced by inner
enamel epithelium) between the two tissues.
These molecules when combined with the
surface receptors of dental papillary cells
causes differentiation of odontoblasts.
2. It provides a spatial configuration to which
mesenchymal cells can react.

• Most teratogenic agents interfere with,
and adversely effect, normal
odontogenesis by:
(1) inhibiting and retarding
polysaccharide and glycoproteins
synthesis, as well as
(2) arresting, in general the formation of
extracellular matrix.


Histophysiology and Clinical Cosiderations


• Initiation


• Tooth may develop in abnormal
location (ovary or hypophysis).
• A lack of initiation results in anodontia
(partial or complete).
• Abnormal initiation results in the
development of single or mutiple
supernumerary teeth.

• Proliferation


•

A disturbance in proliferaton has
different effects, according to:

1. The time of occurrence.
2. The stage of development.


• Histodifferention


• In vitamine A deficiency the
ameloblasts fail to differentiate
properly resulting in formation of
osteodentin.


• Morphodifferention


• Endocrine disturbances affect the size
or form of the crown if it occurs during
morphodifferentiation (in utero or in the
1st year of life).


• This disturbance may affect the form
and size of the tooth without impairing
the function of the ameloblasts or
odontoblasts.


• Hypopituitarism and hypothyroidism
results in small clinical crown and
retarded eruption.


Disturbance may also results in:
1. New parts may be differentiated
(supernumerary cusps or roots).
2. Twinning may occur.
3. A suppression of parts may occur
(loss of cusps or roots).
4. A peg or malformed tooth
(Hutchinson’s incisors in individual
born with congenital syphilis).

• Apposition


•

Disturbance during:

1. Matrix formation
2. Mineralization

E. or D. hypoplasia.
E. or D. hypocalcification.


Tooth development 3 /certified fixed orthodontic courses by Indian dental academy

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