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The
primitive oral cavity is also known as the |
Stomodeum
|
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The
epithelial lining of the primitive oral cavity is best described as |
Stratified
squamous epithelium |
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The
buccopharyngeal membrane is formed by |
Oral
ectoderm and endoderm of foregut |
|
The
buccopharyngeal membrane ruptures & the primitive oral cavity establishes a connection with the foregut at about the |
27th
day of gestation |
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The
dental lamina forms when the human embryo is |
6
weeks old |
|
The
dental lamina serves as a primodium for the |
Ectodermal
portion of teeth. It serves as a primodium for the ectodermal portion of the deciduous teeth. |
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The
development of the 1st permanent molar is initiated at |
4th
month intrauterine life |
|
The
development of the 2nd permanent molar is initiated at |
1st
yr after birth |
|
The
bud of non-successional permanent teeth develops from lamina due to |
Distal
proliferation. Or as a distal extension of the dental lamina. Sometimes this distal extension extend deep in to the ramus causing the development of teeth (especially third molars) in the ramus. |
|
The
bud of successional permanent teeth develops from lamina due to |
Lingual
proliferation. Or as a lingual extension of the free end of the dental lamina opposite to the enamel organ of each deciduous teeth. |
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The
development of successional lamina extends from |
Fifth
month intrauterine life to 10 months of age |
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The
activity of the dental lamina extends over a period of at least |
5years
|
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The
vestibular lamina is located _________ to the dental lamina |
Buccal
|
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The
lip furrow band is also known as |
Vestibular
lamina |
|
The
first deciduous tooth bud to be formed is in the |
Anterior
maxilla |
|
The
development stages of teeth are named after the shape of |
Epithelial
component |
|
In
bud stage of teeth development, enamel organ consists of |
Peripheral
low columnar cells & central polygonal cells |
|
The
local grouping of ectomesenchymal cells that fails to produce extracellular substances and not separated from each other in and around the enamel organ is referred to as the |
Condensation.
Induction is the ability to induce changes or differentiation. Maturation is the cells attaining the features and characteristics it was designed to show and differentiation is the ability of a group of developing cells to change from one group to other with new characteristics under some influence. |
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The
area of ectomesenchymal condensation sub adjacent (below) to enamel organ is |
Dental
papilla |
|
The
condensed ectomesenchyme that surrounds the tooth bud is the |
Dental
sac |
|
The
dental papilla will give rise to |
Pulp
and dentin. By the inductive effect of the inner enamel epithelium, the superficial ectomesenchymal cells of dental papilla differentiate in to odontoblasts that form the dentin. |
|
The
dental sac will give rise to |
Cementum
and periodontal ligament. Once the epithelial root sheath of Hertwig is broken the newly formed radicular or root dentin is exposed and exerts an inductive influence on the dental sac or follicle cells to form the cementoblast and the periodontal ligament. |
|
Cap
stage is the stage where the enamel organ undergoes |
Proliferation.
Unequal proliferation and enlargement of the enamel organ and tooth bud is a characteristic feature of the stage. The type and place of proliferation depends upon the type of teeth. |
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In
cap stage of teeth development, the inner enamel epithelium is |
Tall
columnar and in concavity |
|
In
cap stage of teeth development, the outer enamel epithelium is |
Cuboidal
and in convexity |
|
During
odontogenesis, the layer which has a cushion like consistency & gives support to the delicate enamel forming cells is the |
Stellate
reticulum |
|
Parts
of tooth bud |
Epithelium
and central cell |
|
Parts
of enamel organ |
Inner
and outer enamel epithelium, stellate reticulum and stratum intermedium |
|
The
enamel pulp of the enamel organ is also called |
Stellate
reticulum |
|
Stellate
reticulum in bell stage of odontogenesis is rich in |
Albumin.
Inner dental epithelium demonstrates high quantities of glycogen, Stratum intermedium is rich in alkaline phosphatase and capillaries do not come inside this epithelial part of the tooth bud. The cells of stellate reticulum are formed by the fluid accumulation between the polygonal cells of the tooth bud. They assume a branched reticular form and rich in albumin content turning them mucoid or mucinous. This gives a cushioning effect as well as to serve for increased nutritional demand latter. |
|
Structure
in enamel organ that does not disappear before enamel formation begins is |
Enamel
cord and Enamel knot |
|
A
localized, transient epithelial thickening of inner enamel epithelium in bell stage of odontogenesis is |
Enamel
knot |
|
A
localized, linear, transient epithelial thickening of inner enamel epithelium extending to outer enamel epithelium in bell stage of odontogenesis is |
Enamel
cord. It is also known as the enamel septum that divides the tooth in to two halves and is reported to be involved in the determination of the initial position of the first cusp to be formed and by cusp pattern by differential cell division. Enamel niche is an artifact created by the plane of section, where it creates an illusion of a tooth germ having a double attachment by a double strand. |
|
The
layer of cells which have been demonstrated to have a high degree of metabolic activity in bell stage of teeth development is the |
Stratum
intermedium. Well developed cytoplasmic organelles, high amounts of acid mucopolysaccharides and glycogen deposits indicate the high metabolic activity that is carried out in this layer. |
|
The
inner enamel epithelium differentiates in to the ameloblasts in the |
Late
bell stage |
|
The
organizing influence of the inner enamel epithelium on the surrounding ectomesenchyme forms the |
Odontoblast.
The dentin and dentin matrix are secreted by the odontoblasts. Cementum is by the inductive influence of radicular dentin on the cells of the dental follicle or dental sac. |
|
The
layer that is associated with enamel formation other than inner enamel formation in bell stage of odontogenesis is the |
Stratum
intermedium. This layer is closely associated with enamel formation which comes from the histological proof that it is absent in those part of tooth germ that out lines the tooth germ but does not form the enamel. |
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During
the transition from bell to late bell stage of odontogenesis, expansion of stellate reticulum occurs by accumulation of |
Accumulation
of fluids |
|
Stellate
reticulum starts to collapse just before the |
Enamel
formation. It happens just before the enamel is formed. This event begins at the height of cusp or incisal edge. This reason for this is debated. Older view is that it occurs to reduce the distance between ameloblasts and the capillaries near the outer enamel epithelium, as the nutrients cannot diffuse the newly formed dentin and enamel. Now it is argued that the collapse is due to the continuous differential cell division adjacent to the areas of the cusp tip towards the outer enamel epithelium and is purely due to pushing nature of the cells. |
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The
shape of outer enamel epithelium in bell stage of tooth development is |
Low
cuboidal. From the cuboidal shape in cap stage it flattens and forms folds on its outer surface during the enamel formation bringing the much needed nutritional supply closer to the ameloblasts, hence this functional adaptation. |
|
Membrana
preformitiva separates |
Enamel
organ and dental papilla. It is the basement membrane. |
|
Membrana
preformitiva appears |
Prior
to dentin formation |
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The
organizing influence of the inner enamel epithelium on the surrounding ectomesenchyme is evident in the |
Bell
stage. It is seen as a cuboidal cell that latter turn in to a columnar form to produce the dentin. |
|
Before
the formation of the dental tissues the fibers of the dental sac are arranged in |
Circular
fashion, Just like a capsule |
|
The
acellular zone of dental papilla in bell stage of odontogenesis contains |
Aperiodic
fibrils. Though it is acellular few collagen like fibrils with out the periodic banding is observed in this otherwise empty space. |
|
The
epithelial remnants called the cell rests of Malassez are found in the |
Periodontal
ligament of erupted teeth |
|
Cell
rests of Malassez are the remnants of the |
Hertwig’s
epithelial root sheath |
|
The
shape of a crown is primarily determined by the |
Cessation
of mitotic division. In the bell stage, the differential cessation of the mitotic division of the inner enamel epithelial cells brings about the shape of a crown. |
|
The
number of blood capillaries in dental papilla increases during |
Histodifferentiation.
This occurs maximally at the initiation of crown stage of tooth formation. |
|
Development
of root formation begins after the enamel and dentin deposition reaches the |
Future
cementoenamel junction |
|
Prior
to root formation, the Hertwig’s epithelial root sheath forms the |
Cervical
loop. Just prior to the root formation a bend at the area where inner and outer enamel epithelium meets forms the epithelial diaphragm at the area of future cementoenamel junction. |
|
If
the continuity of the Hertwig’s epithelial root sheath is broken prior to dentin formation, a defect in the pulp wall occurs with no |
Dentin
and cementum. Often seen in pulpal floor of furcation and is the cause of accessory root canal formations. This defect is localized and often very small. |
|
The
proliferation of the cells of the epithelial diaphragm is accompanied by proliferation of the cells of the connective tissue of the |
Pulp
|
|
Enamel
pearls are sometimes found in |
Furcation
area of roots of permanent molars. This occurs when the cells of the Hertwig’s epithelial root sheath remain adherent to the radicular dentin and becomes active to produce the enamel. |
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The
crown stage of tooth development begins with |
Dentin
deposition |
|
As
a result of lack of initiation the tooth that is most commonly missing is |
Upper
lateral incisor |
|
Histodifferentiation
succeeds the stage of |
Proliferation
|
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The
process of histodifferentiation reaches highest in the |
Bell
stage |
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An
important stage of morphodifferentiation in the crown, outlining the future dentinoenamel junction is evident in |
Advanced
bell stage |
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Morphodifferentiation
is impossible without |
Proliferation
|
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Disturbances
in morphodifferentiation will not affect the |
Function
of ameloblasts. It may form supernumerary cusp or roots, twinning, loss of cusps or roots and malformed teeth. |
|
Apposition
is the physiologic process relating to the |
Formation
of enamel & dentin matrix |
Which teeth of
|
Molars
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Prof. Rooban Thavarajah
Oral and Maxillofacial Pathologist
List