Embryology Flashcards
In the early embryo the stomodeum is separated from the fore gut by the?
buccopharyngeal
membrane.
The buccopharyngeal
membrane is laterally bordered by?
The first pair of branchial or pharyngeal arches.
The first arch forms paired maxillary
and mandibular processes that grows
and eventually fuse to form the?
Upper and lower jaws respectively
Three distinct processes
all happening concurrently happen to form structures of the face and skull. Name them?
Formation of the upper lip
Formation of the palate
Formation of the lower jaw
Described how the secondary palate is formed?
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).
How do the lips form?
Upper lips form by fusion of the medial nasal
process with the two maxillary processes.
How do cleft lips and palates occur?
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.
What does dental embryology rely on?
relies on induction
What is the process of dental embryology induction?
Interaction occurs between ectoderm
and mesenchymal tissue.
The primitive oral cavity is lined by?
ectoderm.
How is the dental lamina formed?
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
Where do placodes form and what are they?
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.
Discuss the bud stage and its relation to the enamel organ?
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.
How is the dental papillae formed?
The mesenchyme within the confines of the
bell forms the dental papilla, from which the
dentine and pulp would develop.
Which three structures together are referred to as the tooth germ?
The enamel organ
The dental papilla
The dental sac
Mesenchyme surrounding the bell shaped enamel organ forms the?
Dental sac from
which the periodontium will develop.
The outer layers of the dental papilla in contact with the inner enamel
epithelium induces the latter to differentiate into?
Pre-ameloblasts and
later to Ameloblasts.
The inner enamel epithelium induces the outer layers of mesenchyme
of the dental papilla to differentiate into?
Odontoblasts.
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?
Dentino-enamel junction (DEJ)
The odontoblasts produce?
predentin inwardly away from the DEJ (dentino-enamel junction)
Once the crown is fully formed and eruption starts what begins to form?
Root formation begins.
Where does Hertwig’s Root Sheath originate from?
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.
What determines
the root shape and induces production of root dentin?
Hertwig’s Root Sheath.
What happens to Hertwig’s Root Sheath?
It disintegrates and the epithelial remnants remain as epithelial rests of Malassez within
the mature periodontal ligament.
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.
During crown and root formation the mesenchyme of
the dental sec starts to form the?
Dental alveolus and
the periodontal ligament
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.
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
When is primary dentin produced?
Primary dentin is produced before
eruption of the teeth.
When is secondary dentin produced?
Secondary dentin is produced after
eruption and continues throughout life:
initially very rapidly and progressively
slower.
When is tertiary or reparative dentin produced?
Tertiary dentin (or reparative dentin) is
produced in response to tooth damage.
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
How thick is enamel in cats and dogs?
Enamel in dogs and cats are less than
1mm thick
At eruption the apex of the teeth are
open; the apices of the permanent canine
teeth in dogs closes at?
8 months of age
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
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.
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.
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.
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
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.
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.
The lower lip and jaw is formed by fusion of the?
mandibular prominences of the first
brachial arch.
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.
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)
What structures are formed during the cup stage?
Enamel organ
Dental sac
Dental Papilla
These are collectively known as the tooth germ
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.
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.
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.
What is the Stratum intermedium?
This more densely arranged layer forms just above the inner enamel epithelium.
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.
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.
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.
Odontoblasts remain vital within the pulp but what happens to
ameloblasts?
They are lost during tooth eruption.
What does the dental sac (aka dental follicle), differentiate into?
other tissues components of the periodontium (the gingiva, periodontal ligament, cementum, and alveolar bone.)
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.
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)
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.
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
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.
What creates the dentino-cemental junction?
This the formation of cementum on the root dentin, creates the dentino-cemental junction.
What forms the cemento-enamel junction?
The cementum at the neck of the tooth forms the cemento-enamel junction.
What are the cell remnants of Hertwig’s root sheath called?
Epithelial rests of Malassez aka Cell rests of Malassez
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
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.
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.
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
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.
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.
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.
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.
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.
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.
