palatal development Flashcards
function of soft palate
Closes off nasal passages during swallowing
Protects the nasal cavity during sneezing
Involved in speech and sounds
function of hard palate
Separates the nasal cavities from the oral cavity
Important for mastication and speech
Ridges (rugae) help movement of food towards pharynx
how is the primary palate formed?
- mesial growth of the maxillary processes towards nasal processes
- is not able to fuse due to nasolacrimal and bucconasal grooves
- mesial nasal processes grow towards each other and merge
- forms philtrum
- forms region of maxilla carrying incisor teeth
- forms primary palate
- fusion between the maxillary process and lateral aspects of the medial nasal processes = lateral aspect of upper lip
what prevents the fusion of the primary palate?
Fusion is prevented by the nasolacrimal and bucconasal grooves.
when does the secondary palate become visible?
when does the development of the secondary palate begin?
As the medial nasal processes and maxillary prominences fuse the primary and secondary palates become visible as outgrowths.
- begins at the 6th week of gestation (or E13.5 in mice) and completes in the third month
- Week later in females
what is the importance of the secondary palate and it’s fusion?
Development of secondary palate is required to separate the nasal and oral cavities
- oronasal cavity mainly occupied by the tongue
The secondary palate composes more than 90% of the hard and soft palates
what are the palatal shelves?
mesenchyme (neural crest) surrounded by a thin layer of oral epithelium
what regulates palatal outgrowth?
- Shh
- FGF-10 -
- receptor is FGFR2b
- Positive feedback loop
how does BMP regulate palatal outgrowth?
- crosstalk between Shh and BMP signalling
- Smo is transmembrane receptor required for Shh signalling
- decreased Smo = increased BMP4 and decreased BMP2
- BMP2 is a positive regulator of mesenchymal cell proliferation
- decreased Smo = increased BMP4 and decreased BMP2
how occurs when there is disruption of signalling?
give rise to cleft lip and palate
(reduction in anterior palatal mesenchymal cell proliferation)
how do matrix proteins regulate palatal outgrowth?
ADAMTS = family of enzymes (metalloproteinases)
- Bind to cell surface and degrade (proteolysis) extracellular matrix components
Disruption in genes encoding for ADAMTS 9 and 20 result in cleft palate
hoes does palatal shelf elevation take place?
when does it occur?
at week 8 of gestation
- palatal shelves elevate to horizontal position above tongue
- rapid
what are the theories for palatal shelf elevation ?
Rapid rotation of the shelves (Walker and Fraser 1956)
Growth based regression of distal region and outgrowth in horizontal direction (Lazzaro 1940)
why do the palatal shelves elevate?
Ferguson (1981) proposed that the shelves initially grow vertically due to space restraints in the oronasal cavity
- tongue
what extrinic forces are there in palatal elevation?
Downward movement of the tongue - mandibular growth spurt
Downward displacement of the tongue by the nasal septum
Lowering of the tongue due to a foetal mouth opening reflex
Physical pushing of the shelves upwards by the tongue
do extrinsic forces take part in palatal shelf elevation?
no
- Prescence and growth of tongue does not significantly influence palatal shelf elevation
what intrinsic forces may have a role in palatal elevation?
forces from
- hyaluronan
- mesenchymal palatal cells
- epithelium
how may hyaluronan generate force for palatal shelf elevation?
Regional accumulation of glycosaminoglycans (GAGs), mainly hyaluronan (HA)
HA binds water = increase in osmotic pressure
Increase in water in extracellular matrix
- > increase in turgidity of palatal shelves
- > shelf elevation
how do mesenchymal palatal cells contribute to palatal shelf elevation?
Shelf elevation is associated with a change in density and distribution of mesenchymal cells
- Increase in cell density = cell division (closely packed before elevation)
- Decrease in cell density = role of extracellular matrix
Change in shape indicates the cells are contracting
- Change forces in the shelves
Mesenchymal palatal cells have
- Definitive role in maintaining and controlling events within the palatal ECM
how does epithelium contribute to palatal shelf elevation?
Removal of oral cavity facing epithelium = delayed palate elevation
oral epithelium divides more rapidly
Bundles of type I collagen extend down to the vertical tip of the shelf
Influence on the contraction of the palatine mesenchymal cells (via neurotransmitters)
how does adhesion of the palatine shelves occur?
Adhesion first occurs in the middle-anterior region
- first via desmosomes contact
development of midline epithelial seam (MES) - two basal epithelial cell layers
keratin fibrils and desmosomes upregulated in MES to strengthen bond between mesial epithelial edge cells (MEE)
what occurs after MES is formed?
MES thins to a 2/3 cell thick layer
- Growth of palate in oronasal height
- Epithelial cell migration into oral and nasal aspects
- Apoptosis
- Epitheliomesenchymal transformation (EMT)
- Cells change
how does fusion of the palatine shelves take place?
Approximate each other close to midpoint
Fuse anteriorly & posteriorly from that point
Fusion of palatal shelves with each other and nasal septum separates nasal cavities and oral cavity
- For fusion to occur epithelial covering of individual palatine shelves must be removed
- MES must be removed for continuation of mesenchymal tissue
how does palatal bone formation take place?
Ossification from 4 centres of ossification - appear at 8th week
- One in each developing maxilla
- Lies above developing canine tooth germ
- One in each developing palatine bone
- Region forming future perpendicular plate
Incomplete ossification of the palate from these centres defines the median and transverse palatine sutures
what are the severities of cleft palate? how do they occur?
Interruption to any process during to palate formation can result in clefting
Disruptions occurring at earlier stages of palatogenesis result in most severe clefting of the secondary palate
The mildest form of cleft palate involves only the uvula and occurs at late palate development (malfusion)
when are dental malformations associated with cleft palate?
when the alveolus is involved
