Biomineralisation in dentistry Flashcards
Define
- crystal
- crystallization
Mention the two main pathways which enables crystallisation
Crystal:
• A crystal is a solid material where atoms, molecules, or ions are arranged in an orderly, repeating pattern that extends in all three spatial dimensions.
Crystallization:
• Crystallization is the (natural or artificial) process of formation of solid crystals precipitating from a solution, melt or more rarely gas
Two main pathways of crystallisation
• Crystallization from solution: The crystals form by precipitating from a solution (solvent) at room temperature.
• Melt crystallization: The crystals from when two or more substance with similar melting points are separated by some degree of cooling. It doesn’t involve solvents.
Define biomineralization and define the two types of biominerals
Biomineralization:
• Refers to the processes by which organisms form minerals often to harden or stiffen existing tissues
Two types of biominerals:
• Amorphous biominerals: without a clearly defined shape or form
• Crystallized biominerals: have a intricate, complex shape/ structure that is mostly uniform throughout and very distinct
Explain what is meant by “ crystallised biomineralization is a matrix mediated process” by using dentine as an example
- Dentine is primarily made of proteins
- Proteins acts as a form of support on which hydroxyapatite crystals are deposited
- If proteins were absent, the hydroxyapatite structure would collapse
- Thus, biomineralization is a “matrix mediated” process -> a form of support is needed for mineralisation to occur. This matrix provides mechanical stability and affinity for minerals
Explain the process of crystallisation by mentioning the two main steps
- Nucleation
• The initial process that occurs in crystal formation from either a solution, liquidor a vapour
• Here, small number of ions, atoms, or molecules become arranged in a pattern characteristic of a crystalline solid
• Thus, solute molecules dispersed in the solvent start to gather into clusters, elevating solute concentration in that region. These stable clusters constitute the nuclei - Crystal growth:
• Additional crystals begin depositing on the nuclei until it grows into a larger size
Define an ionic solid and explain the 2 forces that affect the solubility of an ionic solid
Ionic solid:
· Ionic solidsare salts, such as NaCl, that are held together by the strong force of attraction between ions of opposite charge
Two forces act in opposition when determining the solubility of an ionic solid. These are:
- Aggregation or formation of the solid state (crystallization, precipitation): favoured by the strength of attraction between ions (ion-ion interaction)
- Dispersion or formation of the dissolved state (dissolution): favoured by attraction between ions and solvent (ion-dipole interaction)
In nucleation (and thus crystal formation), we want to favour the force of aggregation over the force of dispersion.
Using NaCl as an example, explain how the force of aggregation can be overpower the force of dispersion
- Salt stays in dissolved form because the Na+ and Cl+ are both coated by molecules of water, thus keeping them separate
- Thus, to encourage crystalline formation, the solvent which is water, is removed
- The positive and negative charges are attracted to each other and come together, forming crystals (known as solution- solid transition)
Explain what affects the rate of precipitation
- The higher the concentration of the ions, the faster this process
- The higher the affinity of the two ions, the faster this process
Define Ksp (solubility product constant) and state what values mean
- Even the most insoluble products will dissolve to a tiny extent in a solution if it is present in large amounts
- Ksp provides insight into the equilibrium between the solid solute and its constituent ions that are dissociated across the solution.
- The smaller the Ksp, the less soluble the substance is = more crystal formation
- The larger the Ksp, the more soluble the substance is
- Therefore, this tells how easy the process of nucleation will be for each crystal
When ionic product is equal to ksp, what biological process occurs?
- In this condition the solution is set to be saturated
- There is no change in dissolution or precipitation as forces are in equilibrium
- Therefore, no change occurs
When the ionic product is larger than the Ksp, what biological process occurs?
- In this condition solution is undersaturated
- Dissolution is the favoured response
- Therefore, demineralisation of bone and teeth may occur
When the ionic product is lower than the Ksp, what biological process occurs?
- In this condition solution is supersaturated
- Precipitation is the favoured response
- Therefore, there is the formation of bone, enamel and calculus
Discuss why nucleation is a tricky process for biological entities
It is impossible for a biological system to encourage crystal formation by removing a solvent like how is done with NaCl
List and describe the characteristics of slightly soluble salts in terms of:
- Which state they are stable in
- The ion charge and the effect of this
- Packing amount
State they are stable in:
• Stable in the solid state
The ion charge and the effect of this;
• Ions have high charge density (thus more attraction)
Packing amount:
• They pack to maximize separation of same-charge ions and minimize separation of opposite-charge
List and describe the characteristics of the two different types of highly soluble salts
- Which state they are stable in
- The ion charge and the effect of this
- Packing amount
- Attractions
Which state they are stable in:
• Stable in the dissolved state
The ion charge and the effect of this:
• Ions have low charge density (thus less attraction)
Packing amount:
• Pack relatively poorly
Attractions:
• Are attracted to H2O
Describe the properties of hydroxyapatite
- Empirical formula: Ca10(PO4)6(OH)2
- Has very low solubility at a pH of 7
- It has a low Ksp, meaning its solubility is very low and therefore it should form precipitates faster
- NaCl has high solubility (high Ksp) and thus it should take longer to form precipitate
- However, it is very difficult to form hydroxyapatite
