L2 Palatal Growth Flashcards
Describe the soft palate.
- 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
Describe the hard palate.
- Anterior
- Immovable horizontal bone plate
- Seperates nasal cavities from oral cavity
- Important for mastication and speech
- Rugae for movement of food towards the pharynx
Fusion of which processes forms the primary palate?
Fusion of the medial nasal processes forms the intermaxillary segment which gives rise to the primary palate.
Describe the formation of the secondary palate.
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.
What is the palate proper?
The developed palate, a fusion of the primary and secondary palates.
What are the palatal shelves composed of?
They are mesenhymal in origin, and surrounded by a layer of oral epithelium.
Palatal shelf outgrowth is strictly controlled, name the 4 main factors involved.
- Sonic hedgehog
- FGF-10
- BMP
- ECM proteins
How does Shh regulate palatal shelf outgrowth?
- Expressed throughout the oral epithelium, signals to underlying mesenchyme
- Causes palatal cell proliferation and shelf outgrowth
How does FGF-10 regulate palatal shelf outgrowth?
- FGF-10 is found in mesenchyme and FGFR2b is found in the epithelium
- Interaction between the 2 causes palatal cell proliferation and shelf outgrowth
How does BMP regulate palatal shelf outgrowth?
- 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
How do ECM proteins regulate palatal shelf outgrowth?
- 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)
What happens at 8 weeks i.u. with regards to palatogenesis?
- 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)
Describe extrinsic factors involved in palatal elevation.
- 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.
Describe intrinsic forces involved in palatal elevation.
- 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
Describe the role of mesenchymal palatal cells in palatal elevation.
- 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
Describe the role of the epithelium in palatal elevation.
- Removal of oral epithelium caused delayed elevation
- Removal of nasal epithelium had no effect on shelf movement
Not understood why this occurs.
What stages do the palatal shelves undergo after elevation?
- Adhesion
- Fusion
Describe adhesion of the palatine shelves.
- 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
Describe fusion of the palatine shelves.
- 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
Describe palatal bone formation.
- Ossification centres appear at week 8
- There is 1 centre in each maxillary process and each developing palatine bone (4 centres in total)
What do malformations in palatogenesis cause?
Cleft palate.
What causes cleft palate?
- Genetic factors
- Environmental factors e.g. X-rays during pregnancy
When will clefting be most severe?
When disruptions occur at earlier stages of palatogenesis.
When will cleft palate most likely cause dental malformations?
- When the alveolus is involved
What are the 6 types of cleft palate defects?
- Cleft of lip and alveolus
- Cleft of lip and primary palate
- Unilateral cleft lip and palate
- Bilateral cleft lip and primary palate
- Bilateral cleft lip and palate
- Cleft palate only
