L3 Prenatal Jaw Development Flashcards
Which tissue does the skull develop from?
From the mesenchyme surrounding the developing brain.
What can occur if the neurocranium does not form or mineralise correctly?
Craniosynotosis: early fusion causing abnormal skull shape
Apert syndrome: coronal sutures affected, cranium adopts, tower shaped skull
What does the viscerocranium refer to and when does it begin developing?
The bones of the face, including the jaws.
Begins to develop around week 4 i.u.
What is the viscerocranium divided into?
- The membranous viscerocranium
- The chondral viscerocranium
What is the origin of the viscerocranium?
Develops from the 1st and 2nd pharyngeal arches, therefore of mesodermal origin.
It is formed by migrating neural crest cells.
The 1st pharyngeal arch is divided into 2 parts, what are these and what do they give rise to?
- Maxillary process gives rise to the maxilla, zygomatic and temporal bones
- Mandibular process gives rise to the mandible
What is contained within each pharyngeal arch?
- A cartilaginous rod
- Muscle
- Nerve
- Artery
Outline the main steps of mandible development.
- Meckel’s cartilage acts as a template to support mineralisation
- The mesenchymal tissue surrounding the cartilage undergoes ossification (begins laterally) to form the mandible
- The cartilage is then lost
Describe mandible development at week 6.
- Meckel’s cartilage runs from the otic capsule to the midline
- Meckel’s cartilage takes the form of a hyaline cartilage rod surrounded by a fibro-ceullular capsule (periochondrium)
- 2/3rds along the cartilage the mandibular nerve divides into the lingual and inferior alveolar nerve
- The inferior alveolar nerve divides into the incisive and mental nerves - this point is where the underlying mesenchyme condenses and mineralisation begins
Describe mandible development at week 7.
- Intramembranous ossification of the mesenchyme begins
- There is an anterior spread of bone along the lateral aspect of Meckel’s cartilage which forms a trough of medial and lateral bony plates
- These plates unite beneath the incisive nerve and later inclose the nerve creating the incisive canal
Describe mandible development at week 10.
- Meckel’s cartilage forms the malleus and spheno-mandibular ligaments
- Meckel’s cartilage begins to be resorbed
- Some evidence suggests Meckel’s cartilage contributes to mandible formation via endochondral ossification as well- particularly in the condylar region
Describe mandible development at week 12.
- Condylar cartilage appears (different to Meckel’s)
- Forms a cone shaped mass occupying most of the developing ramus
- Rapidly mineralised to bone via endochondral ossification
Describe mandible development at week 20.
- A thin layer of cartilage remains at the condylar head, persists until 2nd decade of life
- Secondary cartilage appears called coronoid cartilage (later fuses with ramus and disappears before birth)
- Symphysial cartilages appear between the 2 ends of Meckel’s cartilage which fuse with the mandible and disappear in the 1st year of life
Which part of the 1st pharyngeal arch does the maxilla develop from?
The ventral region of the viscerocranial mesenchyme of the maxillary process of the 1st arch.
Describe maxilla development at week 8.
- Centre of ossification appears close to the site of the developing deciduous canine, where the anterior superior alveolar nerve and infra orbital nerve divide
- Bone spreads anteriorly towards incisor region and superiorly to the frontal processes and zygomatic processes
- Bony trough forms from the infra-orbital nerve which extends downwards to form the lateral alveolar plate around the maxillary tooth germs
- Ossification spreads towards palatine processes to form the hard palate
What secondary cartilage is present in maxilla development?
- Zygomatic/malar cartilage appears in developing zygomatic process and helps development
When does the maxillary sinus form?
At week 16, on the nasal aspect of the developing maxilla.
Name 4 similarities in mandible and maxilla development.
- Both develop from single centres of ossification in close relation to bifurcating nerves
- Both develop an alveolar element related to the developing teeth
- Both develop secondary cartilages to assist growth
- Bulk of bone formed by intramembranous ossification
Name 2 differences between mandible and maxilla development.
- There is no primary cartilage in maxilla development
- The mandibular condyles are formed by endochondral ossification
Which cell type do osteoblasts develop from?
Mesenchymal stem cells
What type of bone is formed during development?
Woven bone: weak, not dense
Also first bone type formed in fracture repair
What type of bone is found lining the tooth socket?
Bundle bone (histologically similair to woven bone) Also called the lamina dura
Explain intra-membranous ossification.
- MSCs differentiate to osteoblasts
- Osteoblasts secrete osteoid
- Matrix-mediated mineralisation occurs
Explain endochondral ossification.
- Chondrocytes undergo proliferation and hypertrophy
- Cartilage ECM forms trabeculae and mineralises
- Chondrocytes die
- Bone marrow cells and BVs evnter
- Lining osteoblasts form lamellae and ECM, ultimately mineralises to become bone
- Mineralised cartilage is degraded
What are the components of the alveolar process?
- The inner and outer alveolar plates
- Lamina dura
- Alveolar crest (where the plate meets the lamina dura)
- Supporting cancellous bone
What are the inner and outer alveolar plates made of?
Compact bone
What is the lamina dura made of?
Bundle bone
What is the lamina dura also known as?
The cribriform plate
- Perforated by foramina called Volkman’s canals which carry nerves and blood vessels
- It is embedded with extrinsic collagen fibres from the PDL (Sharpey’s)
