CFD 18 - biological mineralisation

Question 1

What are the benefits of fluoride ion substituting OH ion in hydroxyapatite?

Answer 1

• stabilises the lattice
• more acid resistant

Question 2

What is the critical pH of hydroxyapatite, and of fluorapatite?

Answer 2

hydroxyapatite: pH 5.5
fluorapatite: pH 4.5

• fluorapatite required larger pH fall to result in dissolution of mineral

Question 3

What are the 3 theories of mineralisation?

Answer 3

• alkaline phosphatase hypothesis
• nucleation theories:
  
  • (homogenous nucleation)
  • heterogenous nucleation
• matrix vesicles

Question 4

What is the alkaline phosphatase hypothesis?

Answer 4

alkaline phosphatase enzyme
- hydrolyses organic phosphates
- releases inorganic phosphates

Robison 1923

Question 5

What are the problems with the alkaline phosphatase hypothesis?

Answer 5

• (organic phosphates) too low to be an effective source
• other sites contain alkaline phosphatase e.g. kidney
• normal serum (phosphate) is sufficient

Question 6

What is the theory of homogenous nucleation?

Answer 6

• the formation of a 1st solid from a solution of ions in which no solid previously existed
• serum contains calcium and phosphate ions… can hydroxyapatite crystals form??

Question 7

What has been shown about the theory of homogenous nucleation?

Answer 7

• homogenous nucleation of hydroxyapatite is very difficult to achieve
• hydroxyapatite crystals do no spontaneously form in the blood stream
• ions in serum can sustain crystal growth

Question 8

What is the theory of hetergenous nucleation?

Answer 8

• epitaxy
• a foreign solid will assist nucleation of a crystal
• theory that something else acts as a template for crystals to grow on/promotes the growth of crystals

Question 9

What are the possible nucleation for the heterogenous nucleation theory?

Answer 9

• collagen
  
  • 64nm spacing will allow nucleation
  • collagen fibrils in bone and dentine different to collagens elsewhere
• proteoglycans
• lipids
• phosphoproteins

Question 10

What are matrix vessels?

Answer 10

• produced by cells
• contain high concentrations of calcium and phosphate ions
• provide ideal microenvironment for crystal formation and growth
• released into extracellular tissue
• crystals grow and rupture vesicle

Question 11

What do matrix vesicles help to do?

Answer 11

help initiate mineralisation in a tissue

Question 12

What is the sequence of mineralisation for a tooth?

Answer 12

1. dentine
2. enamel
3. cementum

Question 13

What are matrix vesicles involved in the formation of?

Answer 13

the first formed dentine (the outer/mantle dentine)

Question 14

What is responsible for mineralisation initiation?

Answer 14

• epitatic (template) properties of matrix - heterogenous nucleation
• matrix vesicles help initiate initial mineralisation of dentine

Question 15

What is responsible for subsequent mineralisation?

Answer 15

• heterogenous nucleation
• crystal growth in supersaturated serum