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PRENATAL DEVELOPMENT OF THE JAWS

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PRENATAL DEVELOPMENT OF THE JAWS AT BIRTH At birth the mandible is in its physiological rest position. The relative lack of growth of the lower jaw prenatally also ... – PowerPoint PPT presentation

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Title: PRENATAL DEVELOPMENT OF THE JAWS


1
PRENATAL DEVELOPMENT OF THE JAWS
2
  • Many of the problems that result in
    craniofacial anomalies arise in the early stage
    of the embryonic development.
  • in order to recognize the developmental
    abnormality, as soon as possible and
  • to assess the aetiology of malocclusions
  • the authorities are more considered with
    developmental processes of the jaws and teeth.

3
DEVELOPMENT OF THE FACE
  • Development of the face starts from ventral
    part of the head process of an embryo and the
    first branchial arch.
  • The face develops mainly between the 4th and 8th
    weeks.
  • By the end of the embryonic period ( eight
    weeks ) the face has an unquestionably human
    appearance.

4
DEVELOPMENT OF THE FACE
  • The first branchial arch develops two elevations
    called the maxillary prominence and
    mandibular prominence.
  • In the 4th week the five facial primordia are
    around the stomodeum ( primitive mouth )
  • The large frontonasal prominence constitutes
    the cranial boundary of the stomodeum.
  • The paired maxillary prominences of the firsth
    branchial arch form the lateral boundaries and
  • the paired mandibular prominences of the same
    arch constitute the caudal boundary of the
    stomodeum.

5
Early formation of the face about 24 days after
conception
  • Scanning electron
    micrographs of an embryo

6
Bilateral oval-shaped thickenings of the surface
ectoderm, called nasal placodes, develop on
each side of the caudal part of frontonasal
elevation
  • Horseshoe-shaped medial and lateral
    prominences develop at the margins of the nasal
    placodes. As a result, the nasal placodes lie in
    depressions called nasal pits.

7
  • The maxillary prominences grow rapidly and
    soon approach each other and the medial nasal
    prominences. During the 6th and 7th weeks the
    medial nasal prominences merge with each other
    and the maxillary prominences.

8
Diagrammatic representation of the structures at
the beginning of the 5th week when fusion is just
beginning.Relationship at the beginning of the
6th week, when the fusion is well
advanced.Schematic representation of the
contribution of the embryonic facial processes to
the structures of the adult face
9
DEVELOPMENT OF THE FACE
  • As the medial nasal prominences merge with
    each other, they form an intermaxillary
    segment of the maxilla. This segment give rise
    to
  • the middle portion of the upper lip called the
    philtrum
  • the premaxillary part of the maxilla and its
    associated gingiva
  • the primary palate
  • The lateral parts of the upper lip, most of the
    maxilla and the secondary palate form from the
    maxillary prominences.
  • These prominences merge laterally with the
    mandibular prominences

10
DEVELOPMENT OF THE FACE
  • The mandibular prominences merge with each other
    in the fourth week and the groove between them
    disappears before the end of the fifth week.
  • The mandibular prominences give rise to
  • the mandible
  • lower lip and
  • the inferior part of the face
  • The frontonasal prominence forms the forehead and
    the dorsum and apex of the nose.
  • The sides of the nose are derived from the
    lateral nasal prominences.

11
DEVELOPMENT OF THE PALATE
  • The palate develops from the
  • the primary palate and
  • the secondary palate
  • Although palatogenesis begins toward the end of
    the 5 week, fusion of the palates parts is not
    complete until the 12 week.

12
DEVELOPMENT OF THE PALATE
  • The primary palate or median palatine
    process, develops at the end of the fifth week
    from the innermost part of the intermaxillary
    segment of the maxilla.
  • It forms a wedge-shaped mass of mesoderm between
    the maxillary prominences of the developing
    maxilla.

13
DEVELOPMENT OF THE PALATE
  • The secondary palate develops from two
    internal projections from the maxillary
    prominences, called the lateral palatine
    processes.
  • These shelflike structures inicially project
    inferomedially on each side of the tongue. As the
    jaws develop, the tongue moves inferiorly and the
    lateral palatine processes gradually grow toward
    each other and fuse. They also fuse with the
    primary palate and nasal septum.

14
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15
  • The fusion of the palatal processes begins
    anteriorly during the 9th week and ends
    posteriorly in the region of the uvula by the
    12th week. The palatine raphe indicates the line
    of fusion of the lateral palatine processes. The
    posterior portion of the lateral palatine
    processes do not become ossified. They extend
    beyond the nasal septum and form the soft palate
    and uvula.

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17
  • The failure of fusion of the facial processes
    give rise the group of anomalies called clefts.
  • Bilateral cleft lip and palate in an infant.
  • The separation of the premaxilla from the
    remainder of the maxilla caused by failure of
    fusion between medial nasal prominences and
    maxillary prominences.

18
  • Cleft of secondary palate caused by failure of
    fusion of the palatal shelves.

19
  • Unilateral cleft of lip, the medial nasal and
    maxillary prominences fail to fuse only on the
    right side.

20
  • Table shows the embryonic development in the
    time and the related syndromes that may arise in
    these periods.

21
Fetal alcohol syndrom
22
Treacher Collins syndrome (mandibulofacial
dysostosis)
23
Hemifacial microsomia
24
Crouzons syndrome
25
DEVELOPMENT OF THE CRANIAL BASE AND JAWS
  • The bones of the cranial base are formed
    initially in cartilage and are transformed by
    endochondral ossification to bone.
  • Picture shows the chondrocranium at 8 weeks
    of intrauterine development. A continuous plate
    of cartilage extends from the nasal capsule
    posteriorly all the way to the foramen magnum at
    the base of the skull.

26
DEVELOPMENT OF THE CRANIAL BASE AND JAWS
  • Cartilage is a nearly avascular tissue whose
    internal cells are supplied by diffusion through
    the outer layers. This means, of course, that the
    cartilage must be thin. At early stages in
    development, the extremely small size of the
    embryo makes a chondroskeleton feasible, but with
    further growth, it is no longer possible without
    an internal blood supply.
  • During the fourth month in utero, there is an
    ingrowth of blood vascular elements into various
    points of the chondrocranium (and the other parts
    of the early cartilaginous skeleton). These areas
    become centers of ossification, at which
    cartilage is transformed into bone, and islands
    of bone appear in the sea of surrounding
    cartilage

27
DEVELOPMENT OF THE CRANIAL BASE AND JAWS
  • The cartilage continues to grow rapidly but is
    replaced by bone with equal rapidity. Eventually,
    the old chondrocranium is represented only by
    small areas of cartilage interposed between large
    sections of bone.
  • Not all bones of the adult skeleton were
    represented in the embryonic cartilaginous model,
    and it is possible for bone to form by secretion
    of bone matrix directly within connective
    tissues. Bone formation of this type is called
    intramembranous bone formation. This type of
    ossification occurs in the cranial vault and both
    jaws

28
DEVELOPMENT OF THE CRANIAL BASE AND JAWS
  • The mandible of higher animals develops in the
    same area as the cartilage of the first
    pharyngeal arch-Meckel's cartilage.
  • It would seem that the mandible should be a
    bony replacement for this cartilage. In fact,
    development of the mandible begins as a
    condensation of mesenchyme just lateral to
    Meckel's cartilage and proceeds entirely as an
    intramembranous bone formation.
  • Meckel's cartilage largely disappears as the
    bony mandible develops. Rests of this cartilage
    are transformed into a portion of two of the
    small bones of the middle ear. Its perichondrium
    persists as the sphenomandibular ligament

29
DEVELOPMENT OF THE CRANIAL BASE AND JAWS
  • The condylar cartilage develops initially as an
    independent secondary cartilage, which is
    separated by a considerable gap from the body of
    the mandible Early in fetal life it fuses with
    the developing mandibular ramus.
  • A Separate areas of mesenchymal condensation, at
    8 weeks.
  • B Fusion of the cartilage with the mandibular
    body, at 4 months
  • C Situation at birth.

30
DEVELOPMENT OF THE CRANIAL BASE AND JAWS
  • The maxilla forms initially from a center of
    mesenchymal condensation in the maxillary
    process.
  • This area is located on the lateral surface of
    the nasal capsule, the most anterior part of the
    chondrocranium.
  • Although the growth of the chondrocranium
    contributes to lengthening of the head and
    anterior displacement of the maxilla, it does not
    contribute directly to formation of the maxillary
    bone.

31
  • In term of orthodontics the most important thing
    is the different growth pattern of the maxilla
    and mandible during the antenatal life. As a
    result the antero-posterior relationship of jaws
    is changing.

32
  • The tongue and mandible of the 6-8 week-old
    embryo are posteriorly positioned relative to the
    maxilla. It is 1th embryo mandibular
    retrognathism.
  • Within the next month mandible tends to grow
    faster then maxilla. This change allows
    depression of the tongue from common oral and
    nasal cavity to oral cavity. The tongue is
    loosing the contact with the nasal septum and the
    oral and nasal cavities can be isolated by the
    connecting palatal proceses. This state is called
    the embryo mandibular prognatism.

33
  • During the last period of antenatal development
    the accelerated growth of cranial cavity and the
    upper facial skeleton causes the 2th embryo
    mandibular retrognathism.

34
AT BIRTH
  • At birth the mandible is in its physiological
    rest position. The relative lack of growth of the
    lower jaw prenatally also makes birth easier,
    since a prominent bony chin at the time of birth
    would be a considerable problem in passage
    through the birth canal.
  • By the age of 6 month mandible will have reached
    the right position relative to the maxilla. It is
    probably due to the muscle function during the
    sucking.

35
AT BIRTH
  • Appearance of the jaw relief reflects their
    complicated development.
  • The alveolar arches, also called the gum-pads are
    horse-shoe shaped in the maxilla and U-shaped in
    the mandible.
  • They are low and the vault of the palate is very
    shallow.
  • The alveolar part is separated on its palatal
    side from the hard palate by a continuous
    horizontal groove known as the "dental or
    gingival groove".

36
AT BIRTH
  • In the frontal region the groove is bridged by
    incisal papilla and the gum pad along with
    anterior part of palate form the "incisal
    plateau".
  • At birth the maxillary and mandibular gum-pads
    have 20 segmented elevations corresponding to the
    unerupted deciduous teeth.
  • The groove that marks the distal margin of the
    canine segment continues into the buccal sulcus
    and is called the lateral sulcus.

37
AT BIRTH
  • The gum-pads rarely come into occlusion. They
    are separated verticaly when at rest. When
    pressed against each other they are mostly still
    separated anteriorly, and the space sometimes
    extends backwards as far as the canine region.
    Transversally, the upper alveolar arch is
    slightly wider than the lower one.

38
AT BIRTH
  • If the incisal plateau is horizontal, there is
    no overlaping of the gum pads and the lower gum
    pad occlude with incisal plateau about 2-8 mm
    posteriorly to its border because of mandibular
    rest position.
  • The other extrem is the very sheer plateau
    witch completely overlaps the lower gum pad. Its
    usually a predecessor of later Class II Division
    2 of Angles classification (deep bite and
    retroclination of upper incisors because of
    theirs sheer position). The majority cases are
    betwen these two extremes.

39
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