OE L5 Dentine Matrix Proteins Flashcards
Where is mineral deposited in dentine?
At the mineralisation front.
How is mineral deposited in circumpulpal dentine?
Matrix mediated mineralisation.
Gloubles called calcospherites grow in size and fuse to form inetrubular dentine.
How does matrix mediated mineralisation occur?
Caused by a variety of ECM interactions and protein modifications.
What are the 2 stages of mineral crystal formation?
- Nucleation
2. Crystal growth
Describe nucleation in dentine.
Heterogenous nucleation.
Pre-existing solid phase.
Carboxyl groups of acidic proteins attract calcium, calcium arrangement as a lattice. Binding of phosphate.
Brief summary of mineralisation.
Proteins secreted from odontoblast process facilitates deposition of hydroxyapatite calcium phosphate amongst collagen fibres.
Describe the collagenous matrix in predentine.
Collagen matrix provides a scaffold for eventual dentine formation.
- Primarily type 1 collagen
- Fibrils are crosslinked
- Pyridinoline cross links between lysine and hydroxylysine residues (increase in these links as predentine transitions to dentine)
Where does crystal deposition occur in the collagen fibrils?
- At the gap zone
- Proteins guide mineral to gap zone
- Gap zones and quarter staggered arrangement results in banding pattern
- Means molecules aren’t too close togther so mineral has space to come in
In predentine there are proteins inhibiting this process collagen scaffold must be entirely formed before mineral is added.
Describe hydroxyapatite composition in dentine.
Crystals formed from calcium and phosphate.
Crystals are smaller in dentine than in enamel.
What molecules guide mineral deposition?
- Proteoglycans
- Phosphoprotiens and sialoproteins
- Glycoproteins
Name the key proteoglycans in dentine.
- Decorin
- Biglycan
- Versican
Describe decorin in predentine and dentine.
- In predentine, bound to dermatan sulphate, brings molecules together with correct spacing and correct sized gap zone
- In dentine, bound to chondroitin sulphate, which can bind to calcium and guide it to gap zones
Describe biglycan and decorin in predentine and dentine.
- In predentine, biglycan and decorin is found bound to dermatan sulphate
- In dentine, biglycan and decorin is found bound to chondroitin sulphate
Describe versican in predentine.
- Much larger than decorin and blycan
- Up to 20 chondroitin sulphate chains
- An inhibitor of mineralisation found in predentine
Explain the dentine sialophosphoprotein gene (DSPP).
Transcribes either dentine sialoprotein (DSP) from the 5’ end or dentine phosphoprotein (DPP) from the 3’ end.
Describe dentine sialoprotein.
- Acidic
- Present in odontoblasts, predentine and dentine
- High carbohydrate content
- Phosphorylated
Describe dentine phosphoprotein.
- Rich in serine amino acids
- Rich in aspartic acid
- Promotes heterogenous nucleation
Give examples of non-dentine specific glycoproteins.
- Dentine matrix protein
- Osteopontin (inhibits mineralisation)
- Osteonectin, bone sialoprotein and osteocalcin (promote mineralisation)
Describe the role of matrix metalloproteinases in dentine.
They are involved in remodelling predentine:
- removal of inhibtors of mineralisation
- processing of proteins for new function
E.g. stromelysins, collagenasees, membrane type MMPs
Describe the mineralisation of mantle dentine.
Matrix vesicle mediated mineralisation.
- Vesicles with phospholipid membrane
- Vesicles highly concentrated in calcium, alkaline phosphate and ATP
- Also contain MMPs, phosphoproteins, acidic proteins
- Less mineralised compared to circumpulpal dentine as collagen scaffold is not as organised
Result of mutations in DSPP gene.
Mutations in DSPP gene can cause hypomineralisation (soft teeth).
Types of dentinogenesis imperfecta linked to DSPP gene.
