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Summary- Paediatric Dentistry
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Essay summaries for preclinic of paediatric dentistry, containing topics from histogenesis to dental dysplasia.
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1. Ontogenetic development of the maxillar-facial region.Gastrulation between the 14th and 20th day of development
- Separation of ecto- and endoderm and intercalation of a layer between them called
mesoderm;
- Ectoderm (external layer)- formed of cylindrical cells; gives rise to skin cells of
epidermis; neurons of brain; pigment cells; ENAMEL;
- Endoderm- formed of flat cells, overlaying the inner surface of the gastro-intestinal tract
with exclusion of oral cavity, pharynx, terminal region of rectum; related with the
formation of pancreatic cells, lung (alveolar) cells, thyroid cells;
- Endoderm does not take part in the building-up of oral cavity structures.
- Mesoderm- consists of large-sized cells with vast intercellular spaces full of
intercellular substance;
- Mesoderm (middle layer) gives rise to cardiac muscle tissue, skeletal muscle cells,
tubule cells of the kidney, red blood cells, smooth muscle tissue
Neurulation (20th -21st day)
- Formation of the primitive brain→ prosencephalon, mesencephalon,
rombencephalon;
- 3 cerebral ventriculi play role in the formation of the structures of the
maxilla-facial region.
Formation of primary mouth and oro-pharynx
- During the 4th embryonic week- formation of the oral pit.
- 20th -25th day of embryonic growth- formation of the primary mouth
/STOMADEUM
- The primary mouth and the upper part of digestive tube, named pharynx, give rise
to a structure called oro-pharynx.
,Formation of the branchial /cartilage/ apparatus
On the 4th embryonic week- formation of branchial arches, grooves and membranes.
- The 1st BRANCHIAL ARCH /MADIBULAR ARCH/- related with the formation of
mandibular and maxillar projections, trigeminal nerve, porus acusticus externus.
- The 2nd BRANCHIAL ARCH /HYOID ARCH/- related with the formation of hyoid
bone and facial nerve.
- The 3rd BRANCHIAL ARCH- related with the formation of the hyoid bone and
glossopharyngeal nerve.
- The 4th and 6th BRANCHIAL ARCH- related with the formation of thyroid region
and nervus vagus.
- The 5th Branchial Arch in humans is in a state of total regression.
Development of the oro-facial region
4th EMBRYONICWEEK
- On the 4th embryonic week the HEART gets into function.
- 30th 35th day of the embryonic growth- formation of the lower jaw /MANDIBLE/ of
the 2 mandibular projections through processes of evagination, medialization,
mesodermization.
- From the frontal-nasal projection originate the nasal pits. These are bilateral
prominences of the ectodermal layer.
- In the process of medialization the lateral nasal projection is closing the outer line
of maxillar projection. From the nasal-lacrimal groove originates naso- lacrimal
canal.
5th EMBRYONIC WEEK
- The nasal pits are developing into nostrils.
- Formation of an internasal zone.
- On both sides of head eyes are being formed.
6th EMBRYONIC WEEK
- Enlargement of the face in lateral direction as a result of enlargement of brain.
- Formation of the right and left ear canal.
- Formation of the upper lip and both of the maxillar segments.
- Both of the medial nasal projections close to one another and forming the
PHILTRUM.
,7th EMBRYONIC WEEK
The frontal-nasal projection gives origin of:
- The middle part of upper lip and philtrum
- The middle part of upper jaw and attached gingiva
- The primary hard palate /medial palatal projections.
Both of the maxillar projections give origin of:
- Side parts of upper lip;
- Side regions of upper jaw and attached gingiva;
- Secondary hard palate /lateral palatal projections.
Development of nose and nasal cavity
- By oro-nasal membrane nasal conchae remain separated from oral cavity.
- the oro-nasal membrane the nasal and oral cavity are connected by the
means of the primitive choana.
- By septum nasi the nasal cavity is divided into two parts- left and right. Each
of them is characterized with 3 conchae- concha nasalis superior, concha
nasalis media, concha nasalis inferior.
Development of palate: During the period between 8th and 10th embryonic week;
- The secondary hard palate is formed of both of maxillar palatal projections
and horizontal lamina of palatal bone.
- As a result of mesodermization of palatal projections the nasal septum is
formed.
- Primary and secondary hard palate are being connected to the level of
foramen incisivae and totally accomplish the building-up of hard palate.
Development of hard palate
- Process of ossification of primary and secondary hard palate.
- The medial nasal projection gives rise to the nasal septum which connects
with the palate in vertical direction. Oral and nasal cavities are separated
from one another.
Development of tongue
- The (Pharyngeal) back 1/3 of the tongue is built of 2 mesodermal
invaginations of the 1st , 3rd and 4th branchial arch.
- The (oral) frontal 2/3 and back 1/3 of the tongue are connected into sulcus
terminalis.
- the tongue fills both of the nasal and oral cavities.
- After formation of the palate tongue is located into oral cavity.
, RELATIONS OF JAWS
- On the 60th -65th day of the embryonic development- formation of upper jaw;
- Embryonic prognathia- till the 65th day of embryonic development the
tongue fills up nasal and oral cavities;
- Embryonic progenia- after separation of oral and nasal cavities, the tongue
exercises pressure upon lower jaw;
- Neonatal prognathia- upper jaw outstrips in its development lower jaw;
-
2. Morphological and biological characteristics of the tooth germ.
Initiation of tooth development
- With primary mouth formation – stomadeum (4th e.w.) the future jaws are
only jaw shafts, and the thickenings on their ridge are called jaw rods.
- By high mitotic division of the epithelium cells a small thickening is formed
on the ridge of the jaw shaft – jaw rod.
- The basal membrane separates the both layers - ecto- and mesodermal.
- begins with a thickening on the ridge of lamina dentis
- “Initiation of tooth germs” - ten ectodermal invaginations with ten cell
aggregations are formed in depth of each dental lamina – future deciduous
teeth
- new oral proliferation of dental lamina for permanent incisors, canines and
premolars – lamina dentis secundaria
- new distal proliferation of dental lamina for the first, second and third
permanent molar
Proliferation
- Stages: formation of jaw shafts, jaw rods, lamina vestibularis, lamina dentis
- As a result of mitotic division of ectodermal cells - jaw rods
- Ectomesenchymal cells congregate around jaw rods under the basal lamina
- Two new proliferations into the mesoderm – lamina vestibularis and
lamina dentis
Lamina vestibularis and dentis
- Lamina vestibularis – vestibular proliferation of ectodermal cells in
mesoderm – future vestibulum oris.
- Lamina dentis – oral proliferation of ectodermal cells, called “odontogenic
ectoderm”, because of its ability to produce teeth
Hysto- and morphodifferentiation
• Hystodifferentiation – a process, during which histologically different cells
are being formed – different in shape, size and function
• Morphodifferentiation – different layers with cells with same function
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