Suture Development

• show the 2 main regions of the skull

  - neurocranium/cranial vault

  - viscerocranium/ cranial base

  
• how much of the head is the new borns face?

  1/8th

  - this changes to about 1/2 by adulthood
• What is different about the parietal & frontal bones?

  They are flat bones

  
• What are sutures?

  Fibrous joints between the skull bones, which provide some elasticity & movement. They're generally unfused at birth.

  
  

  - continuous growth of the skull relies on the sutures remaining patent (open and unfused)
• What are the different sutures of the skull?

  Sagittal suture

  Coronal suture

  Interfrontal/metopic suture

  
• what causes the zigzag of sutures?

  growth of the brain pushes the skull bones out and this results in tension at the sutures. This tension induces new bone growth.
• What are fontanelles?

  Membrane covered spots in the calvaria where 3 or more bones converge. They're larger than sutures at birth but rapidly diminish in size as calvarial bones grow

  
• At what times do the different fontanelles grow?

  Anterior fontanelle (2 yrs)

  Posterior fontanelle (first few months)

  Sphenoidal fontanelle (first few months)

  Mastoid fontanelle (first few months)

  
  

  - the bones grow more or less in parallel to eachother
• What does continuous growth of the skull rely on?

  Sutures remaining patent (open & unfused) as premature fusion leads to craniosynostosis
• What does the orientation of facial sutures determine?

  Direction of facial growth
• What does a mature suture look like?

  - capsular layer has few cells

  - cambian layer lines the edge and it is where bone formation occurs

  
• describe bone formation at the sutures

  - undifferentiated mesenchymal cell responds to growth factors from the surrounding regions tissues

  - this causes the undifferentiated mesenchymal cell to become the osteoprogenitor (immature bone cells)

  - the osteoprogenitors line the bone and form mature bone cells/osteoblasts which lay down more bone matrix which mineralises and generates new bone

  
• What is palatal expansion using distraction osteogenesis?

  Force is applied using an expansion screw which can separate the 2 halves of the maxillary complex. Tension induced bone growth & deposition at the intermaxillary/palatine suture results in maxillary expansion
• show the sutures of the palate

  
• what happens to the palate sutures as an individual grows into adulthood?

  the sutures fuse and close

  
• what is palatal expansion?

  palate expanders widen narrow upper jaws.

  
  

  - the expander works by turning a key inside the center of the expander. The turn of this key will push the arms of the expander.

  - the tension induces bone growth and deposition at the intermaxillary/palatine suture results in maxillary expansion

  
• What is craniosynostosis?

  premature closure of cranial sutures which causes the underlying brain to be constrained and so it will grow at other sutures.

  
  

  - occurs in 1:2500 live birthds
• What is plagiocephaly?

  Premature closure of the coronal or the lambdoid suture on one side only.

  The cranium is twisted and asymmetrical

  
• What is trigonocephaly?

  Premature closure of the metopic suture

  
• What is scaphocephaly?

  Premature closure of the sagittal suture

  The anterior fontanelle is small or absent

  Long narrow wedge shaped cranium (mohawk looking)

  
• gene causing craniosynostosis

  
  

  What is Apert Syndrome and what does it look like?

  Mutation in FGFR2 receptor which results in midface malformations including malocclusion of teeth, delayed eruption, unusual palatal morphologies (narrow palate, lateral swellings of gum, cleft soft palate, bifid uvula etc.)

  
• gene causing craniosynostosis

  
  

  What is Crouzon syndrome?

  Mutation in FGFR2 or 3, characterised by abnormal calvarial shape ("cloverleaf skull"), shallow orbits with exophthalmos, mid facial hypoplasia.

  dental- crowing, x bites, ectopic eruption of 6's

  
  

  They have normal hands though, unlike Apert syndrome

  
• What are FGF (fibroblast growth factor) receptors?

  Transmembrane receptors, meaning they stick out of the cell & receive signals from adjacent cells
• during bone development at sutures, FGF is a growth factor that causes the undifferentiated mesenchymal cells to become osteoprogenitor cells. How does this occur?


  via gene twist which leads to differentiation/Pre-osteoblast development
• What are FGF receptors capable of?

  Turning on twist expression
• why are mice used to study human disease?

  •Examine function by observing consequences of disrupting a gene in a mammalian system

  •Make mutations that mimic human genetic mutations

  •Easy to do experiments: small, easy to grow

  •Mutant mouse serves as a reagent for both basic studies and pharmaceutical applications
• how were the mice with craniosynostosis used to model and understand the disorder?

  a drug was used to inhibits FGF receptor activation and it showed the normal situation where the parietal and frontal bones go back to being 2 independent bones with an intervening coronal suture.

  
  

  - this showed that the over activation of the FGF receptor has caused the craniosynostosis and that the drug that inhibited the FGF receptor prevented the sutures from fusing.
• explain how craniosynostosis occurs

  FGF receptors are mutated so they are activated with or without ligand (depending on the type of mutation) and this leads to too much twist gene and too much bone formation which leads to closure of sutures.

  
  

  -HYPOTHESIS (this is what we think is happening after doing research using mice)
• craniosynostosis (mostly) caused by gene mutations lead to other phenotypes. give some examples that are related to dentistry.


  - anomalous oral cavities

  - anomalous palates

  - hypodontia

  - peculiar anatomy of gums