palatal development

Question 1

function of soft palate

Answer 1

Closes off nasal passages during swallowing

Protects the nasal cavity during sneezing

Involved in speech and sounds

Question 2

function of hard palate

Answer 2

Separates the nasal cavities from the oral cavity

Important for mastication and speech

Ridges (rugae) help movement of food towards pharynx

Question 3

how is the primary palate formed?

Answer 3

• 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

Question 4

what prevents the fusion of the primary palate?

Answer 4

Fusion is prevented by the nasolacrimal and bucconasal grooves.

Question 5

when does the secondary palate become visible?

when does the development of the secondary palate begin?

Answer 5

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

Question 6

what is the importance of the secondary palate and it’s fusion?

Answer 6

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

Question 7

what are the palatal shelves?

Answer 7

mesenchyme (neural crest) surrounded by a thin layer of oral epithelium

Question 8

what regulates palatal outgrowth?

Answer 8

• Shh
• FGF-10 -
  
  • receptor is FGFR2b
• Positive feedback loop

Question 9

how does BMP regulate palatal outgrowth?

Answer 9

• 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

Question 10

how occurs when there is disruption of signalling?

Answer 10

give rise to cleft lip and palate

(reduction in anterior palatal mesenchymal cell proliferation)

Question 11

how do matrix proteins regulate palatal outgrowth?

Answer 11

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

Question 12

hoes does palatal shelf elevation take place?

when does it occur?

Answer 12

at week 8 of gestation

• palatal shelves elevate to horizontal position above tongue
  
  • rapid

Question 13

what are the theories for palatal shelf elevation ?

Answer 13

Rapid rotation of the shelves (Walker and Fraser 1956)

Growth based regression of distal region and outgrowth in horizontal direction (Lazzaro 1940)

Question 14

why do the palatal shelves elevate?

Answer 14

Ferguson (1981) proposed that the shelves initially grow vertically due to space restraints in the oronasal cavity

• tongue

Question 15

what extrinic forces are there in palatal elevation?

Answer 15

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

Question 16

do extrinsic forces take part in palatal shelf elevation?

Answer 16

no

• Prescence and growth of tongue does not significantly influence palatal shelf elevation

Question 17

what intrinsic forces may have a role in palatal elevation?

Answer 17

forces from

• hyaluronan
• mesenchymal palatal cells
• epithelium

Question 18

how may hyaluronan generate force for palatal shelf elevation?

Answer 18

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

Question 19

how do mesenchymal palatal cells contribute to palatal shelf elevation?

Answer 19

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

Question 20

how does epithelium contribute to palatal shelf elevation?

Answer 20

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)

Question 21

how does adhesion of the palatine shelves occur?

Answer 21

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)

Question 22

what occurs after MES is formed?

Answer 22

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

Question 23

how does fusion of the palatine shelves take place?

Answer 23

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

Question 24

how does palatal bone formation take place?

Answer 24

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

Question 25

what are the severities of cleft palate? how do they occur?

Answer 25

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)

Question 26

when are dental malformations associated with cleft palate?

Answer 26

when the alveolus is involved