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z basic sciences > pre-natal jaw development > Flashcards

pre-natal jaw development Flashcards

1
Q

what 2 mineralised regions is the skull made up of?

A

Neurocranium

  • protective case for the brain

Viscerocranium

  • Jaw skeleton
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2
Q

why did the neurocranium form? in evolution

A

Neurocranium formed in response to expanding brains of fish ancestors

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3
Q

what is the viscerocranium derived from - evolutionary?

A

Skeletal elements of viscerocranium derived from fish gills

  • Branchial arches modified from primitive fish gill bars
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4
Q

what is the neurocranium divided into?

A

Membranous neurocranium

  • Consists of flat bones surrounding brain.

Cartilaginous neurocranium (Chondrocranium)

  • Bones at base of skull.
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5
Q

what are the differences in how membranous neurocranium and cartilaginous neurocranium are formed?

A
  • Membranous neurocranium formed by intramembranous ossification.
  • Cartilaginous neurocranium formed by endochondral ossification.

but both are formed by neural crest cells

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6
Q

what can occur when formation and mineralisation of the neurocranium occurs?

A

Craniosynostosis (abnormal skull shape).

  • When formation does not occur as it should

Premature closure & fusion = skull deformities.

  • E.g. Aperts syndrome (coronal sutures).
  • Cranium adopts a ‘tower skull’ to accommodate brain.
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7
Q

what is the viscerocranium formed from? when?

A

Formed mainly from the first & second visceral (pharyngeal) arches (mesoderm origin).

  • First arch gives rise to = Mandibular arch.
  • Second = Hyoid arch.

Develop around week 4.

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8
Q

what is the viscerocranium divided into?

A

membranous viscerocranium

chondral viscerocranium.

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9
Q

what is the viscerocranium formed by?

A

migrating neural crest cells.

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10
Q

what is the membranous viscerocranium divided into?

A

First visceral arch divided into 2 processes :

  • Maxillary process (cranial part)
  • Mandibular process (caudal part)
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11
Q

what does the maxillary process give rise to?

A

Maxilla bone

Zygomatic bone

Temporal bone

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12
Q

what does the mandibular process give rise to?

A

Mandibular bone

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13
Q

what is an important structure in the formation of the mandible??

A

Meckel’s cartilage

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14
Q

what is the role of meckel’s cartilage

A

Matrix template / framework = support

Support mineralisation process

but does not contribute to the mandible itself

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15
Q

how is the mandible formed?

A

Meckel’s cartilage provides a template

Mesenchymal tissue surrounding Meckel’s cartilage undergoes ossification to form the mandible

  • initially on lateral aspect

Meckel’s cartilage is gradually degraded and lost

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16
Q

what occurs during week 6 of intra-uterine life in mandible development?

A
  • meckel’s cartilage extends into hyaline cartilage rod
    • from otic capsule near developing ear to midline fusion
  • 2/3 along the cartilage - mandibular division of CN V divides into ligual and inferior alveolar nerve
    • inferior alveolar nerve then divides into incisive and mental nerves
  • Mesenchymal condensation occurs between incisive & mental nerves
    • Primary site of ossification
17
Q

where is the primary site of ossification?

A

between incisive & mental nerves

18
Q

what occurs during week 7 of intra-uterine life in mandible development?

A

intra-membranous ossification begins

  • bone formation spreads to midline and posteriorly
    • spread along lateral aspect of Meckel’s cartilage forms trough of medial and lateral plates
    • these unite beneath incisive nerve
      • will form incisive canal
  • this spreads to midline but fusion does not occur until after birth
19
Q

what occurs during week 10 of intra-uterine life in mandible development?

A
  • rudimentary mandible is formed by intra-membranous ossification
  • Meckel’s cartilage (B) forms malleus & spheno-mandibular ligament
  • meckel’s cartilage resorbs
20
Q

what occurs during week 12 of intra-uterine life in mandible development?

A
  • condylar cartilage appers
    • forms cone-shaped mass - occupies most of ramus
    • is rapidly converted to bone by endochondrak ossification
21
Q

what occurs during week 20 of intra-uterine life in mandible development?

A
  • thin layer of cartilage remains at condylar head
  • coronoid cartilage appears
    • fuses with ramus and disappears before birth
  • symphysial cartilages appear
    • fuses with ramus and disappears during 1st year of life
22
Q

how does the maxilla develop?

A

Develops from centre (ventral) region of viscerocranial mesenchyme of the maxillary process of 1st arch

No arch cartilage or primary cartilage unlike in mandible

23
Q

what occurs during week 8 of intra-uterine life in maxilla development?

A
  • cartilage of nasal capsule surrounded by MSC, which condense and ossify by intra-membranous ossification
  • centre of ossification = where anterior superior alevolar nerve and infra-orbital nerve divide
  • bone spreads :
    • posteriorly below orbit towards developing zygoma,
    • anteriorly towards incisor region
    • superiorly to form the frontal process.
  • Ossification also spreads to palatine process, forming hard palate
  • Medial alveolar plate develops from junction of palatal process & main body of maxilla & maxillary tooth germs become enclosed in bony crypts.
  • 2° cartilage, the zygomatic (malar) cartilage appears in developing zygomatic process & helps development.
24
Q

what are the similarities in development of the mandible and maxilla?

A

Begin from single centres of ossification in close relation to the bifurcation of nerves.

Both develop an alveolar element, related to developing teeth.

Both develop 2° cartilages to assist in their growth, but no 1° cartilage in maxilla development.

Bulk of mandible & all of maxilla formed by intramembranous ossification.

  • Only mandibular condyles formed by endochondral ossification.
25
Q

what is intra-membranous ossification?

A

E.g. body of mandible & maxilla

  • Bone formation directly within the mesenchyme
  • MSCs differentiation = osteoblasts.
  • ECM synthesis / secretion (osteoid).
  • Matrix-mediated mineralisation.
  • Remodelling / turnover
26
Q

what is endochondral ossification?

A

E.g. mandibular condyle & syphysis, long bones

Hyaline cartilage formation.

  • Chondrocytes undergo proliferation & hypertrophy.
  • Cartilage ECM forms trabeculae & mineralises.
  • Chondrocytes die.
  • Bone marrow cells & blood vessels enter.
  • Lining osteoblasts form lamellae & ECM = bone.
  • Mineralised cartilage degraded.
27
Q

what is the structure of alveolar bone?

A

Alveolar process is part of jaw bone that contains tooth socket

Consists of outer cortical plate, central cancellous bone & bone lining tooth socket

Cortical plates & bone lining socket meet at alveolar crest

Bone lining socket is called bundle bone

28
Q

what are the properties of bundle bone?

A
  • Immature bone (similar to woven bone).
  • Bone lining tooth socket / lamina dura.
  • Perforated by nerves & blood vessels (cribriform plate).
  • Histologically consists of bundles of collagen fibres, arranged in lamellae running parallel to socket.
  • Embedded with extrinsic collagen fibres from PDL (Sharpey’s fibres, SF).

z basic sciences (21 decks)

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