L2 Palatal Growth

Question 1

Describe the soft palate.

Answer 1

• Posterior
• Also called the velum or muscular palate
• Made of muscular fibres encased in a mucous membrane
• Closes nasal passages from oral cavity during swallowing
• Involved in speech

Question 2

Describe the hard palate.

Answer 2

• Anterior
• Immovable horizontal bone plate
• Seperates nasal cavities from oral cavity
• Important for mastication and speech
• Rugae for movement of food towards the pharynx

Question 3

Fusion of which processes forms the primary palate?

Answer 3

Fusion of the medial nasal processes forms the intermaxillary segment which gives rise to the primary palate.

Question 4

Describe the formation of the secondary palate.

Answer 4

Week 6:
The 2 lateral palatal shelves (from the maxillary process) develop behind the primary palate.

Fusion of the palatal processes is complete by the 12th week of development.

Development of secondary palate is required to separate the nasal and oral cavities.

Question 5

What is the palate proper?

Answer 5

The developed palate, a fusion of the primary and secondary palates.

Question 6

What are the palatal shelves composed of?

Answer 6

They are mesenhymal in origin, and surrounded by a layer of oral epithelium.

Question 7

Palatal shelf outgrowth is strictly controlled, name the 4 main factors involved.

Answer 7

• Sonic hedgehog
• FGF-10
• BMP
• ECM proteins

Question 8

How does Shh regulate palatal shelf outgrowth?

Answer 8

• Expressed throughout the oral epithelium, signals to underlying mesenchyme
• Causes palatal cell proliferation and shelf outgrowth

Question 9

How does FGF-10 regulate palatal shelf outgrowth?

Answer 9

• FGF-10 is found in mesenchyme and FGFR2b is found in the epithelium
• Interaction between the 2 causes palatal cell proliferation and shelf outgrowth

Question 10

How does BMP regulate palatal shelf outgrowth?

Answer 10

• BMP2 is a positive regulator of mesenchymal cell proliferation
• Crosstalk between BMP pathways and Shh
• Disruption of BMP signalling leads to cleft lip and palate

Question 11

How do ECM proteins regulate palatal shelf outgrowth?

Answer 11

• ADAMTS are key remodelling enzymes of the ECM
• ADAMTS proteolyse ECM components like versican, which may release bioactive fragments therefore influencing palatal growth
• Research has shown disruption in genes encoding for ADAMTS causes cleft palate (ADAMTS 9 and 10)

Question 12

What happens at 8 weeks i.u. with regards to palatogenesis?

Answer 12

• Palatal shelf elevation
• Elevate to position above the tongue
• Ferguson (1981) hypothesised that shelves initially grow vertically due to space restraints in the oronasal cavity (large tongue)

Question 13

Describe extrinsic factors involved in palatal elevation.

Answer 13

• Downward movement of tongue due to mandibular growth
• Downward displacement of tongue by nasal septum
• Physical pushing of shelves upwards by tongue

However, removal or the tongue still results in palatal elevation.

Question 14

Describe intrinsic forces involved in palatal elevation.

Answer 14

• Palate contains GAGs e.g. hyaluronan, heparan sulphate
• GAG levels differ before and after elevation, possible that the matrix plays a role in generating force within the shelves

Question 15

Describe the role of mesenchymal palatal cells in palatal elevation.

Answer 15

• Cells before elevation are elongated and bipolar, after elevation they become rounded with shorter processes
• Number of nuclear organising regions increases before elevation, decreases after elevation
• The cells themselves may have a role in changing forces within the shelves causing elevation

Question 16

Describe the role of the epithelium in palatal elevation.

Answer 16

• Removal of oral epithelium caused delayed elevation
• Removal of nasal epithelium had no effect on shelf movement

Not understood why this occurs.

Question 17

What stages do the palatal shelves undergo after elevation?

Answer 17

• Adhesion

- Fusion

Question 18

Describe adhesion of the palatine shelves.

Answer 18

• Adhesion begins in the middle-anterior region
• Adhesion of epithelium first occurs via desmosome contacts
• A midline epithelial seam (MES) forms, composed of 2 basal epithelial layers
• Keratin fibrils and desmosomes are upregulated in the MES strengthening the bond between the medial epithelial edge cells

Question 19

Describe fusion of the palatine shelves.

Answer 19

• Palatal shelves change contours and become close at the midpoint
• They then fuse anteriorly and posteriorly from this midpoint
• The midline epithelial seam covering each shelf must be removed for fusion to occur (it thins and breaks up)
• There is an increase in collagens, proteoglycans, vimentin rich CT and tenascin

Question 20

Describe palatal bone formation.

Answer 20

• Ossification centres appear at week 8

- There is 1 centre in each maxillary process and each developing palatine bone (4 centres in total)

Question 21

What do malformations in palatogenesis cause?

Answer 21

Cleft palate.

Question 22

What causes cleft palate?

Answer 22

• Genetic factors

- Environmental factors e.g. X-rays during pregnancy

Question 23

When will clefting be most severe?

Answer 23

When disruptions occur at earlier stages of palatogenesis.

Question 24

When will cleft palate most likely cause dental malformations?

Answer 24

• When the alveolus is involved

Question 25

What are the 6 types of cleft palate defects?

Answer 25

1. Cleft of lip and alveolus
2. Cleft of lip and primary palate
3. Unilateral cleft lip and palate
4. Bilateral cleft lip and primary palate
5. Bilateral cleft lip and palate
6. Cleft palate only