List
Questions
Answer
The
cartilaginous capsules in the cephalic region are
Nasal,
olfactory and optic. They function to protect the sense organ during the
formative stage.
The
nasal, olfactory and optic cartilaginous capsules comprises the
Neurocranium
The
branchial cartilage system also includes
Trabecular
cartilage. It is the cartilage 0. This has migrated to support the
neurocranium.
Chondrocranium
is made up of
Neurocranium
and viscerocranium
The
early chondrocranium can be visualized in the
12th
week of Intrauterine life. A well developed chondrocranium can be visualized
only when the bone and cartilages are formed, which occur after 10th
week of intrauterine life.
Neural
tube is produced by the formation and fusion of
Neural
fold. The nervous system develops as a thickening within the ectodermal layer
at rostral end (neural plate) that forms the raised margins (neural folds).
In this a midline depression (neural groove) is formed. The neural fold folds
itself so that a tube is formed.
The
paraxial mesoderm is situated ___________ to the neural tube
Lateral.
The mesoderm first thickens on each side of midline to form the paraxial
mesoderm. They latter break up to form somites.
The
first somite is the
Occipital.
Each somite has a sclerotome (that forms 2 adjacent vertebrae), a myotome
(that gives rise to muscles) and a dermatome.
The
neural crest cell arises from
Mid
brain and two rhombomeres
 “HOX” family of homeobox genes are not
expressed
Anterior
to rhombomere 3
Migratory
pathway of neural crest cells are formed by the expression of the
Tenascin
Anterior
to rhombomere 3, the gene (s) expressed is / are
MSX
gene; DLX gene; Bar gene
Some
derivatives from the first pharyngeal groove and pouch
External
auditory meatus; Tymphanic membrane and antrum; Pharyngotympanic tube and
mastoid antrum
The
third pharyngeal pouch give rise to the
Inferior
parathyroid gland and thymus. Superior parathyroid gland derives from the
dorsal part of the 4th pharyngeal pouch, Thyroid glands
(parafollicular cells) from the ventral part of the 4th pharyngeal
pouch, Inferior parathyroid gland from dorsal part of 3rd
pharyngeal pouch and thymus from ventral part of 3rd pharyngeal
pouch.
The
inner aspect of first branchial arch is lined by the
Ectoderm
The
inner aspect of the hyoid arch is lined by the
Endoderm.
So is in all other pharyngeal arches (Except the first).
The
maxillary process is formed at about
24th
day of Intrauterine life
The
olfactory placodes develop at the
28th
day of Intrauterine life
The
face develops between
24th
to 38th day of Intrauterine life
In
the 4th – 5th week of human embryo, the depression
between the two nasal processes is the
Frontonasal
process
The
epithelium in the groove of the furrow separating the maxillary and lateral
nasal process forms the
Nasolacrimal
duct
At
the 37th day of intrauterine life the human embryo shows
odontogenic epithelium can be visualized as the parts of the primary
epithelial band in
Inferior
border of maxillary process; Superior border of mandibular arch; Lateral
aspect of medial nasal process. The primary epithelial band is an arch shaped
continuous plate of odontogenic epithelium that forms from 4 separate zones
of epithelial proliferation, the middle two associated with medial nasal
process in the upper arch and two zones in lower arch –one in each process.
Primary
palate is formed by the fusion of
Frontonasal
and medial nasal process
The
secondary palate is initiated at the
7th
to 8th week of Intrauterine life
Secondary
palate is formed by the fusion of
Lateral
nasal processes
The
movement of tongue from its place of formation to its place of function is
during the
7th
to 8th week of Intrauterine life. This happens before the
secondary palate formation begins. As the tongue is withdrawn below the
processes starts to move towards each other and downwards, merging at the
midline.
During
palate formation, the cause of secondary palate closure is due to
Increased
glycosaminoglycans attract water casing turgidity; contractile fibroblasts in
the shelves; Displacement of tongue. The intrinsic force that makes this
event is not determined. The above mentioned are suggested possibilities.
For
the fusion of palatine shelves to occur the epithelium covering the palatine
shelves should be eliminated. This is accomplished by the
Transformation
of epithelial cells to mesenchymal like cells; Migration of epithelium to the
surfaces; Apoptosis of epithelium occurs. It is found out that once 2 shelves
meet; there is a cessation of DNA synthesis and the carbohydrate rich coat
permits adhesion. The events that follow are not clear. The choices mentioned
are described by various research groups.
Initial
development of human tongue is observed during
4th
week
Tuberculum
impair and lateral lingual swelling are associated with
Mandibular
process; Anterior two third of tongue; First brachial arch. They merge with
each other to form a large mass from which the mucous membrane covering the
anterior two third of tongue is formed.
Root
of tongue arises from
Hypobranchial
eminence. It is a large midline swelling developed from mesenchyme of third
arch, which rapidly divides and overgrows the 2nd arch suppressing
its contribution to further tongue development.  It forms the mucous membrane covering the
posterior one third of tongue is formed.
Anterior
copula of the third pharyngeal arch gives rise to
Mucosa
of root of tongue
The
lingual sulcus is created by the
Downward
growth of ectoderm and degeneration. This forms the lingual sulcus and gives
the tongue its mobility space.
Muscle
of tongue arises from
Occipital
somite
The
innervation of tongue is
Trigeminal
nerve; Facial nerve; Hypoglossal nerve. This is due to the unusual
development pattern of tongue. Mucosa of anterior two third is supplied by
trigeminal nerve (5th cranial nerve). Mucosa of posterior one
third is supplied by glossopharyngeal nerve (9th cranial nerve). Motor supply
is via the hypoglossal nerve (12th cranial nerve).
The
secondary growth cartilage of mandible is (are)
Condylar
cartilage; Coronoid cartilage; Symphyseal cartilage
The
condylar cartilage remains active from
12th
to 20th week of intrauterine life. When active it is a cone or
carrot shaped structure.
The
remnants of condylar cartilage remain till
Life
time   
The
coronoid cartilage persist till only
4th
month of intrauterine life
The
centre of ossification of maxilla is closely associated with the cartilage of
Nasal
capsule
The
ossification of mandible begins at
7th
week
The
initial ossification of mandible begins at the
Angle
of division of inferior alveolar and mental nerves
Rudimentary
human mandible can be appreciated at the
10th
week
The
turning of ossification in to mesenchyme away from Meckel’s cartilage is
marked by the
Lingula
The
secondary growth cartilage of maxilla is the
Malar
cartilage
The
dental lamina makes its presence in the human embryo at about
42nd
to 48th day of Intrauterine life. 55 -56th day – bud
stage for deciduous teeth, 14th week – bell stage for deciduous
teeth, bud for permanent teeth, 18th week – dentin and functional
ameloblasts in deciduous teeth, 32nd week – dentin and functional
ameloblasts of some permanent teeth.
Odontogenesis
is a process that is first initiated by factors resident in the
First
arch epithelium
Odontogenesis
in latter stages is maintained by factors resident in the
First arch ectomesenchyme
Specific
and transient expression of ___________gene are observed at potential sites
of teeth formation along the laminar epithelium
BMP-
2, 4
Specific
and transient expression of ___________gene are observed at potential sites
of teeth formation along the ectomesencyme
BMP4,
MSX1, 2
A
process by which a during development a mass of cells transforms itself in to
morphologically and functionally distinct component is termed as
Histodifferentiation
In
bell stage of odontogenesis increased alkaline phosphatase activity is
demonstrated in
Stratum
intermedium. Inner dental epithelium demonstrates high quantities of glycogen
that is essential for its normal function and will be greater demand once the
first layer of dentin is formed.
Dental
lamina usually breaks/ disintegrates up during the
Bell
stage
Shape
of future crown of the tooth is determined at the
Bell
stage
During
bell stage of tooth development, shape of crown is determined by cessation of
mitotic division occurs at
Inner
dental epithelium
The
point at which the ameloblasts first differentiates represent the
Tip
of growth center
Crown
pattern is determined by the differential cell division of the
Inner
dental epithelium
The
crown pattern in a human child include
Incisiform;
Caniniform; Molariform
The
theory that proposes that the factors responsible for tooth shape are
resident in ectomesenchyme and in distinct and graded fields is the
Field
model theory
The
homeobox genes expression involved in the formation of an incisor are
MSX
1,2
The
homeobox genes expression involved in the formation of a canine are
MSX1,2,
DLX2
The
homeobox genes expression involved in the formation of a molariform tooth are
BARX
1, DLX2
The
theory that supposes that a tooth class is derived from a clone of
ectomesenchymal cells programmed by epithelium to produce a teeth of a given
pattern is the
Clone
model theory
The
nerve penetrates the dental papilla after
Dentinogenesis.
Pioneer nerve fibers approach developing tooth during bud stage and form a
plexus around the follicle and penetrate the dental papilla only after the
dentinogenesis.
Initiation
of primary teeth formation occurs during
6th
to 8th week of Intrauterine life
Initiation
of successional teeth formation occurs during
20th
week of Intrauterine life to 10 months
Initiation
of non-successional permanent teeth formation occurs during
20th
week of Intrauterine life to 5th year
Functional
ameloblasts of permanent first molars of humans can be observed by
32nd
week of Intrauterine life
The
gene responsible for most of amelogenin secretion is located in the
X
chromosome –  Xp22.1-Xp22.3 minor in Y chromosome
The
gene responsible for most of tuftelin secretion is located in the
Y
chromosome
Complete
salivary gland development is achieved in the presence of
First
arch ectomesenchyme
The
site of bud clefting during salivary gland formation is determined by the
Contraction
microfilaments of epithelial cells
A
sympathetic innervation of the developing salivary gland is essential for
Acinar
differentiation
A
parasympathetic innervation of the developing salivary gland is essential for
Whole
salivary gland differentiation
The
parotid salivary glands are formed in the
4th
to 6th week of Intrauterine life
The
teeth constitute approximately how much of the surface area of the whole
mouth
They
occupy about 21.1% of the whole mouth, with upper teeth measuring about 24 cm2
and lower teeth 20 cm2. The palate occupies 9.4%, alveolar
mucosa 21.7%, vestibular mucosa 23.4%, ventral surface of tongue and floor of
mouth 12.3% and dorsal tongue 12%.
Dentin
and pulp are similar in
Embryological
development; Histology; Function. Based on the all features dentin arises
from pulp which also provides nutrition, protects and repairs dentin. Hence
this unit is better called as dentin- pulp complex.
The
sense of discrimination observed in tissues of oral cavity is provided by the
sensory receptors in
Periodontal
ligament. Enamel and cementum has no innervations. This sense is partly
attributed to the periodontal ligament fibers.
The
structure (s) that perforate epithelium is (are)
Teeth.
This is a unique feature of oral mucosa. All other structure has epithelial
invaginations with no break in continuity. But in case of teeth there is a
break in continuity of the oral mucosa.
A
typical synovial joint has articular surfaces of bone covered by
Hyaline
cartilage. A typical synovial joint is lined by hyaline cartilage. But
tempromandibular joint has articular surfaces of bone covered by a fibrous
layer that is an extension of periosteum.
Approximately
______ % of human malformations is caused by alteration in a single gene.
10
The
study of developmental defects is
Teratology
The
early phase of human embryonic phase is characterized by
Proliferation
and migration. The first phase of embryonic stage is largely associated with
proliferation and migration, while the second or last phase of embryonic
phase is associated with differentiation or morphogenesis. These two phases
lasts for 4 weeks each and after 8th week the embryo is referred
as fetus when growth and maturation of cells predominate.
The
most vulnerable period of the human gestation to develop congenital defects
is
Second
or late phase of embryo. The first phase of embryonic stage is largely
associated with proliferation and migration, while the second or last phase
of embryonic phase is associated with differentiation or morphogenesis where
there are many intricate embryologic processes.
The
process in which population of cell changes and establishes a new population
of cells with new characteristics is
Differentiation.
The process that initiates the differentiation is induction; the competence
is that ability of the cells to respond to induction to form new set of
cells.
The
fundamental role in patterning is played by
Homeobox
genes. These are a similar region of 180 nucleotide base pairs in various
chromosomes producing the transcription factors. The regulatory molecules of
such an event are the growth factors and retinoic acids.
In
human orofacial embryology, growth factors behave as an
Inductive
agent. Homeobox genes are the one that determines the patterning, Cell
surface receptors bestows competency. Growth factors are the inductive
agents. They can be classified as autocrine and paracrine regulatory agents.
The
patterning is regulated in the intra-cellular area by
Autocrine
and paracrine growth factors are regulatory agents that act via the cell
surface receptors whereas retinoic acids act with intra-cellular receptors.
In
human embryo, the neural crest cells differentiate from
Lateral
aspect of the neutral plate. Though the name indicates to originate from the
crest, they originate from lateral aspect of neural plate. But in avian and
other lower animals they develop from the crest.
Most
of the connective tissue in the head is derived from
Neural
crest cell. During the lateral folding of embryo most of the mesoderm in the
cephalic end is dis-positioned. Therefore most of the connective tissue is
formed by the neural crest and hence the mesoderm in head is often referred
as ectomesenchyme rather than mesenchyme. Migration of neural crest cells
provides the embryonic connective tissue needed for the craniofacial
development.
The
cartilage derived from the branchial system that form the neurocranium is
Trabecular
cartilage. Though the Reiter’s and Merkel’s cartilage belong to the branchial
system, they do not form the neurocranium. Neurocranium is formed by the
occipital, parachordal cartilaginous blocks along with the trabecular
cartilage. This trabecular cartilage is the first cartilage (Cartilage 0)
that has migrated to support the neurocranium.
The
number of rhombomeres formed in human hind brain during the head formation is
Eight.
A series of eight bulges forms along the neural tube in the area of hind
brain called as the rhombomeres.
When
the stomatodeum first forms it is delimited rostrally by neural plate and
caudally by
Cardiac
plate. The buccopharyngeal membrane separates the stomatodeum from foregut,
laterally by pharyngeal arches.
The
branchial arches form in the
Pharyngeal
wall. The branchial arch form in the pharyngeal wall by the result of
proliferating lateral plate mesoderm and subsequent reinforcement by the
neural crest cells.
The
cervical sinus arise from the persistence of
Second
pharyngeal groove; Third pharyngeal groove; Fourth pharyngeal groove. The
overgrowth of second pharyngeal arch normally obliterates the 2nd,
3rd and 4th pharyngeal grooves but sometimes may persists
as a cervical sinus which may or may not drain outside.
The
second pharyngeal pouch is obliterated by the
Developing
palatine tonsil. But a part of this pouch persists in all individuals as the
tonsillar fossa or crypt.
The
post-trematic branch of each branchial arch is the
Sensory
component supplying the epithelium that covers anterior half of arch. The
pre-trematic branch supplies the epithelium that covers the posterior half of
epithelium of the preceding arch.
Union
of palatal processes is best described as
Actual
fusion of processes. Generally ostensible fusion of processes actually
involves the elimination of a furrow at the site of the union. Rarely such as
in this case there is a complete merging and crossing of the tissues.
The
floor of the mouth is formed by the epithelium covering the
Mesenchyme
of the 1st pharyngeal arch; Mesenchyme of the 2nd  pharyngeal arch ; Mesenchyme of the 3rd
pharyngeal arch

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