Embryology Flashcards
(108 cards)
1
Q
In the early embryo the stomodeum is separated from the fore gut by the?
A
buccopharyngeal
membrane.
2
Q
The buccopharyngeal
membrane is laterally bordered by?
A
The first pair of branchial or pharyngeal arches.
3
Q
The first arch forms paired maxillary
and mandibular processes that grows
and eventually fuse to form the?
A
Upper and lower jaws respectively
4
Q
Three distinct processes
all happening concurrently happen to form structures of the face and skull. Name them?
A
Formation of the upper lip
Formation of the palate
Formation of the lower jaw
5
Q
Described how the secondary palate is formed?
A
Secondary palate forms by fusion of palatal shelfs from the side which fuse with the nasal septum in the centre. The palatal shelves also fuse with palatal bone caudally and incisive bone
(primary palate rostrally).
6
Q
How do the lips form?
A
Upper lips form by fusion of the medial nasal
process with the two maxillary processes.
7
Q
How do cleft lips and palates occur?
A
The secondary palate forms by fusion. The palatal shelfs from the side fuses with the nasal
septum in the centre. The palatal shelfs also fuses with palatal bone caudally and incisive bone
(primary palate rostrally).
Upper lips form by fusion of the medial nasal process with the two maxillary processes.
Cartilaginous Chondrocranium eventually ossifies. The first ossification in the mandible occurs
at 27 days (when the embryo is about 17mm long).
Failure of fusion of these parts can cause cleft lips and palates in various combinations.
8
Q
What does dental embryology rely on?
A
relies on induction
9
Q
What is the process of dental embryology induction?
A
Interaction occurs between ectoderm
and mesenchymal tissue.
10
Q
The primitive oral cavity is lined by?
A
ectoderm.
11
Q
How is the dental lamina formed?
A
The primitive oral cavity is lined by ectoderm.
A band of ectoderm along the developing jaws, grows into the mesenchyme to form the dental lamina
12
Q
Where do placodes form and what are they?
A
Along the dental lamina, placodes form and from
these buds are formed where teeth would
develop.
The dental placode is the main epithelial structure participating in tooth formation. The dental placode forms along the dental lamina, rapidly invades the underlying mesenchyme and gives rise to enamel-producing ameloblasts.
13
Q
Discuss the bud stage and its relation to the enamel organ?
A
Along the dental lamina, placodes form and from
these buds are formed where teeth will
develop.
Each bud develops into a cap and eventually a bell
shape. This ectodermal structure forms the
enamel organ, the inner layer of which will
produce the enamel.
14
Q
How is the dental papillae formed?
A
The mesenchyme within the confines of the
bell forms the dental papilla, from which the
dentine and pulp would develop.
15
Q
Which three structures together are referred to as the tooth germ?
A
The enamel organ
The dental papilla
The dental sac
16
Q
Mesenchyme surrounding the bell shaped enamel organ forms the?
A
Dental sac from
which the periodontium will develop.
17
Q
The outer layers of the dental papilla in contact with the inner enamel
epithelium induces the latter to differentiate into?
A
Pre-ameloblasts and
later to Ameloblasts.
18
Q
The inner enamel epithelium induces the outer layers of mesenchyme
of the dental papilla to differentiate into?
A
Odontoblasts.
19
Q
The ameloblasts produce in an outward direction, away from the
dental papilla, enamel ground substance that will be mineralised later.
This contact between enamel and dentin is called the?
A
Dentino-enamel junction (DEJ)
20
Q
The odontoblasts produce?
A
predentin inwardly away from the DEJ (dentino-enamel junction)
21
Q
Once the crown is fully formed and eruption starts what begins to form?
A
Root formation begins.
22
Q
Where does Hertwig’s Root Sheath originate from?
A
The two layers of epithelium at the apical rim of the enable organ grows down into the dental sac and is
called Hertwig’s Root Sheath.
23
Q
What determines
the root shape and induces production of root dentin?
A
Hertwig’s Root Sheath.
24
Q
What happens to Hertwig’s Root Sheath?
A
It disintegrates and the epithelial remnants remain as epithelial rests of Malassez within
the mature periodontal ligament.
25
What causes cementum production?
Undifferentiated mesenchymal cells in contact with root
dentin are induced to differentiate into cementoblasts
and starts to produce cementum on the root surface.
26
During crown and root formation the mesenchyme of
the dental sec starts to form the?
Dental alveolus and
the periodontal ligament
27
How far do collagen fibres extend?
Collagen fibres form that span the periodontal
ligament and these are embedded into cementum on
the tooth side and the developing bone of the
alveolus.
28
What is the function of the periodontal ligament?
The periodontal ligament anchors the tooth in the
alveolus and act as a suspensory system to act as a shock absorber for the tooth
29
When is primary dentin produced?
Primary dentin is produced before
eruption of the teeth.
30
When is secondary dentin produced?
Secondary dentin is produced after
eruption and continues throughout life:
initially very rapidly and progressively
slower.
31
When is tertiary or reparative dentin produced?
Tertiary dentin (or reparative dentin) is
produced in response to tooth damage.
32
When is the enamel of the crown completely formed?
The enamel of the crowns are completely
formed well before eruption. Eruption is usually complete at
about 8 week post partum in dogs
33
How thick is enamel in cats and dogs?
Enamel in dogs and cats are less than
1mm thick
34
At eruption the apex of the teeth are
open; the apices of the permanent canine
teeth in dogs closes at?
8 months of age
35
Root Formation is
unlikely to be an important mechanism for
eruption. What is root elongation more a likely consequence of?
Root elongation is more likely a consequence of
eruption than a cause
36
What is unlikely to be major contribution to eruption?
Bone Remodelling is
unlikely to be a major contributor. Even with a “replacement”
plastic or metal tooth within the follicle, the tooth erupts
normally.
37
How does the dental Follicle play a role in tooth eruption?
The Reduced Enamel Epithelium (REE)
produces proteases which create a path of least resistance for eruption.
38
What may use traction power to assist tooth eruption?
Periodontal Ligament formation and renewal may be a factor in creating a “traction power” to assist in tooth
eruption.
39
The 1st pair of pharyngeal arches develop caudal to the stomodeum. Facial prominences form from the mesenchyme with contributions from the neuroectoderm. Which five prominences can be distinguished?
1 x Fronto-nasal
2 x mandibular prominence
2 x maxillary prominences
40
The maxillary prominences increase and grow medially. This compresses the medial
nasal prominences towards the midline, and these two prominences fuse to form the?
Upper lip.
41
What is left as evidence of the medial nasal prominences fusing to form the lips?
A philtrum, to evidence this fusion, remains visible in animals like carnivores
sheep and goats.
42
The lower lip and jaw is formed by fusion of the?
mandibular prominences of the first
brachial arch.
43
What forms the maxillary segment of the primary palete?
The fusion of the two maxillary prominences at the midline also occurs at a deeper level
and this forms the maxillary segment.
44
The maxillary segment of the primary palate is composed of?
The labial component
(this forms the philtrum of the upper lip)
The upper jaw component (this supports the
incisor teeth)
The palatal component (which forms the triangular primary palette)
45
The inter maxillary segment is continuous with the?
Rostral portion of the nasal septum.
46
How is the secondary palate formed?
The palatine shelves extend downwards from the maxillary prominences on either side of the tongue. As the oral cavity develops and grows, the floor of the mouth with the
attached tongue moves away and the vertical palatal shelves them becomes directed
horizontally and fuses in the midline.
Rostrally the secondary palette fuses to the triangular primary palate. The nasal septum
grows downwards and joins the vomer on the nasal aspects of the newly formed palate.
47
Describe the 1st stage of development of the tongue?
The formation of two lateral
lingual swellings and one medial swelling, the tuberculum impar. These three swellings
arise from the second brachial brachial arch.
48
Describe the second stage of the development of the tongue?
The second median swelling (the copula) forms from the mesoderm of the second, third and fourth arches.
49
Describe the third stage of the development of the tongue?
The third median swelling forms from the caudal aspect of the tongue, from the fourth
brachial arch.
50
The lateral lingual swellings expand and outgrow the tuberculum impar and merge to
form the?
rostral two thirds of the body of the tongue
51
The caudal one third of the tongue arises from the?
second, third and fourth brachial arches.
52
Sensory and motor innovation of the tongue is determined by?
The brachial
arches the specific portion of the tongue is derived from.
53
What innervates the musculature of the tongue?
The hypoglossal nerve
54
The sensory innervation of the body of the
tongue is supplied by the?
mandibular branch of the trigeminal nerve because this part of
the tongue is derived from the first pharyngeal arch.
55
The nerve supply to the root of the tongue originates from the third pharyngeal arch and
therefore the?
glossopharyngeal nerve
56
The extreme caudal portion of the tongue, as well as the epiglottis, originates from the
fourth pharyngeal arch and is therefore innervated by the?superior laryngeal nerve.
superior laryngeal nerve
57
Most of the facial bones form as a result of what type of ossification?
intramembranous ossification.
58
How does intramembranous ossification differ from intrachordal ossification?
As opposed to intrachordal ossification where both interstitial as well as appositional
bone growth occurs, only appositional bone growth occurs in intramembranous
ossification.
59
How does intramembranous ossification work?
sheets of mesenchyme differentiate into osteoblasts
and secrete osteoid matrix. The latter calcifies to form bone spicules that radiates from
centres of ossification to form the trabecular network of cancellous bone (aka as spongey bone)
60
Mesenchyme in close contact with cancellous bone differentiate to form?
Periosteal bone
layers.
This compact bone surrounds cancellous bone in most of the bones of the face
and jaw.
61
What can be considered a guide to mandibular formation?
Meckel’s Cartilage. These bilateral cartilage rods can be considered a guide to mandible formation. Most of the mandible formation is associated with it but only a small portions of this cartilage is included in the final mandible.
62
The chordal aspects of Meckel’s cartilage forms the?
Malleus of the middle ear.
63
The position of dental
placodes determines?
arrangement of both deciduous and permanent teeth along the developing dental arcades of both the upper and lower jaws.
64
Crown development progresses through a few distinct stages namely?
* Bud
* Cup and
* Bell stages.
65
All teeth therefore develop from?
ectoderm and
mesoderm components.
66
What happens in bud stage?
Along the dental lamina, at the dental placodes, the thickening of ectodermal tissue occurs. The ectodermal tissue (the dental lamina ) that forms the buds are still
separated, by means of the basement membrane from the surrounding mesenchyme.
67
What happens in the cup stage?
Proliferation of the tissue of the tooth buds grows into a more cup shaped structure.
Morphogenesis (determines the shape of the developing tooth) is the predominant
process during the stage.
Within the deeper layers of the tooth germ, the enamel organ starts to develop and this
will determine the shape of the crown. The mesenchyme surrounding the tooth bud
starts to organise and will eventually form the dental sac and dental papilla.
This dental papilla remains separated from the enamel organ by the basement
membrane and this layer will eventually disintegrate and be replaced by the
dentinoenamel junction (DEJ).
The dental sack (mesenchyme) will eventually form the periodontium.
At the end of this stage, the structure established is therefore the enamel organ, the
dental sac and the dental papilla and this is collectively known as the tooth germ.
68
What structures are formed during the cup stage?
Enamel organ
Dental sac
Dental Papilla
These are collectively known as the tooth germ
69
What happens at the Bell stage?
Proliferation, morphogenesis, and differentiation of the tooth germ continues. During this stage the inner and outer enamel epithelium is separated by two new layers. The enamel organ have now differentiated into four different and distinctive layers.
70
At the bell stage the enamel organ has now differentiated into four distinctive layers. Name them?
* Inner enamel epithelium (this layer will differentiate to form ameloblasts to produce enamel)
* the stratum intermedium supports enamel production,
* The stellate retinaculum supports enamel production and
* the outer enamel epithelium.
71
Describe the function of the inner enamel epithelium?
This layer differentiates initially into pre-ameloblasts. These cells become progressively more columnar and start the production of ameloid, the enamel ground substance, thestart of amelogenisis.
72
Describe the function of the stellate retinaculum?
This loosely organised layer of reticular cells allow nutrients to reach the inner layers of the enamel organ and provide a protective cushioning layer.
73
Describe the function of the stellate retinaculum?
This loosely organised layer of reticular cells allow nutrients to reach the inner layers of the enamel organ and provide a protective cushioning layer.
74
What is the Stratum intermedium?
This more densely arranged layer forms just above the inner enamel epithelium.
75
What is the dental papilla?
The mesenchyme closely associated with the enamel organ, and later enclosed within the root sheet and developing dentin is called the dental papilla and will eventually form the pulp of the tooth.
76
The mesenchyme of the dental papilla differentiates into two layers: the outermost layer in close contact with the inner enamel epithelium (therefore in contact with the
basement membrane), differentiates into?
Odontoblasts.
These cuboidal cells starts to produce the mucopolysaccharide ground substance of dentin, predentin.
77
What happens to the basement membrane of the dental papilla?
At first it separates the ectodermal and mesodermal components, it goes on to disintegrate and mineralise and eventually forms the dentinoenamel junction.
78
Enamel separates ameloblasts from dentin but odontoblasts maintains contact with?
The dentinoenamel junction via odontoplastic processes within dentinal tubules that radiate outwards from the pulp canal.
79
Odontoblasts remain vital within the pulp but what happens to
ameloblasts?
They are lost during tooth eruption.
80
What does the dental sac (aka dental follicle), differentiate into?
other tissues components of the periodontium (the gingiva, periodontal ligament, cementum, and alveolar bone.)
81
What are the Rests of Serres
During the Bell stage/phase, the dental lamina starts to fragment but some ectodermal remnants of this structure remains in the mesenchyme. These remaining ectodermal cell remnants are referred to as the rests of Serres.
82
Describe reciprocal induction during the bell stage?
*Pre-ameloblasts induce odontoblasts to produce dentin,
* the dentinal matrix induces conversion of pre-ameloblasts to ameloblasts and
* in response, ameloblasts start to produce enamel.
83
what is primary dentin?
Dentin produced before tooth eruption.
84
Describe the formation of primary dentin?
Primary dentin (dentin produced before tooth eruption) continues towards the apex until the latter is completely formed and closes, described as apexogenesis (formation of the apex of the tooth root)
85
When does root development begin?
Once the crown is fully formed and starts to erupt.
86
Where is the cervical loop?
At the most apical part of the enamel organ the inner and outer enamel epithelium are in contact. At this edge these two epithelial layers are called the cervical loop.
87
What happens to the cervical loop?
The cervical loop grows down into the mesenchyme of the tooth germ enclosing the dental papilla and forms Hertwig’s sheath
88
How is Hertwig's root sheath formed?
The cervical loop grows down into the mesenchyme of the tooth germ enclosing the dental papilla and forms Hertwig’s sheath
89
What does Hertwig's root sheath do?
It determines the shape of the roots. The inner layer of Hertwig’s root sheath induces formation of odontoblasts and the
production of dentin of the tooth roots.
90
How is cementum formed?
The basement membrane (of the inner/outer enamel epithelium) as well as Hertwig’s root sheath starts to disintegrate. This creates contact between odontoblasts and mesenchymal cells of the dental sack and this contact induces the differentiation of mesenchymal cells into cementoblasts on the surface of the root dentin and these cells produce cementoid, the ground substance that later mineralise to form cementum.
91
What are cementocytes?
Some cementoblasts are entrapped within the
cementoid and are then referred to as cementocytes.
92
What creates the dentino-cemental junction?
This the formation of cementum on the root dentin, creates the dentino-cemental junction.
93
What forms the cemento-enamel junction?
The cementum at the neck of the tooth forms the cemento-enamel junction.
94
Describe the three configurations of the cemento-enamel junction?
* in 60% of teeth cementum overlaps the enamel
* in 30% of teeth the enamel and cementum abuts and in
* 10% of teeth a small gap remains between cementum and enamel
95
What are the cell remnants of Hertwig’s root sheath called?
Epithelial rests of Malassez aka Cell rests of Malassez
96
Epithelial rests of Malassez cells, stimulated by various processes, play a role in the development of what?
ontogenetic cysts
97
How is the periodontal ligament formed?
During root formation parts of the dental sac organise to become the periodontal ligament. Collagen fibres produced by fibroblasts
becomes embedded in the cementum and extend into the periodontal ligament to meet similar collagen fibres that extend into the periodontal ligament from the developing alveolar bone. This loose connection allows tooth eruption. Once eruption is completed these interwoven collagen fibres are strengthened by additional collagen to form the strong bundles of the periodontal ligament, Sharpie’s fibres. The latter is therefore embedded into cementum on the tooth side, spans the width of the periodontal ligament
and is embedded within the alveolar bone.
98
Describe the five different groups of periodontal ligament fibres?
The alveolar crest group
The horizontal fibre group
The oblique fibres
The apical fibre group
The trans-furcational group of fibres aka intra-radicular
99
Described the function of the alveolar crest group fibres of the periodontal ligament?
these fibres extend from the alveolar margin to the coronal
aspect of the root. It resists intrusion extrusion and rotational forces.
99
Describe the function of the alveolar crest group fibres of the periodontal ligament?
these fibres extend from the alveolar margin to the coronal
aspect of the root. It resists intrusion extrusion and rotational forces.
100
Describe the function of the horizontal fibre group of the periodontal ligament?
these fibres attaches the coronal part of the tooth root to
the alveolus and maintains the tooth's vertical position and resists rotational and tilting forces
101
Describe the function of the oblique fibre group of the periodontal ligament?
The oblique fibre group extends from the alveolar's alveolus in an apical direction to the root surface. They primarily resist intrusion but also counteract rotational forces.
102
Describe the function of the oblique fibre group of the periodontal ligament?
The oblique fibre group extends from the alveolar's alveolus in an apical direction to the root surface. They primarily resist intrusion but also counteract rotational forces.
103
Describe the function of the apical fibre group of the periodontal ligament?
The apical fibre group. These fibres extend from the root apex to the apical alveolus Fibres in arranged in this direction, resists extrusion of the tooth.
104
Describe the function of the trans-furcational group of the periodontal ligament?
The trans-furcational group of fibres. These fibres extends from the furcational bone to the furcation of multi-rooted teeth. These fibre bundles resists intrusion exclusion, tilting and rotational forces.
105
When the crown of the tooth is completely formed and ready to erupt the four layers of the enamel organ do what?
merge into a single layer called the reduced enamel epithelium (REE)
106
Discuss the gubernacular canal?
This chord of ectodermal tissue connects the reduced enamel epithelium to the oral cavity and corresponds to the degenerated dental lamina. This may pay a roll in tooth eruption.
107
Discuss how the reduce enamel epithelium could play a role in tooth eruption?
The reduced enamel epithelium appears to play a significant role in tooth eruption. The reduced enamel epithelium produces proteases that helps to create the eruption path along the gubernaculum. The formation of a gubernacular eruption pathway appears to be associated with the stimulation of cells along this path to form osteoclasts.
