Week 2 - Dental Biomaterials Flashcards
What are the 3 main direct dental restorative materials
- Resin Composites
- Glass Ionomer Materials
- Amalgam
What are resin composites
- polymer material
- Consists of resin matrix and filler particles which are added to reduce shrinkage
What chemical reaction is involved with resin composites
chemical or light activated polymerisation
What are positive of resin composites
- good aesthetic
- Good mechanical strength
- Can be bonded to the tooth using a bonding agent
What are negatives of resin composites
- Technique sensitive
- Discolouration over time
- Polymerization shrinkage
- Doesn’t bond directly
What is addition polymerisation
Addition polymerisation occurs when a reaction between 2 molecules produce a larger molecule without the elimination of a smaller molecule or by product.
What are the steps in addition polymerisation
- Activation
Formation of a free radical - breaks the initiator to free the free radical (through heator light)
- Initiation
The free radical then reacts with a unsaturated monomer binding to it and forming another free radical. The new free radical them binds to another monomer.
- Polymerisation
The radical formed in the initiation step reacts with another monomer, creating a longer chain radical. This process repeats multiple times, rapidly growing the polymer chain.
- Termination
These free radical chains can also bind to other free radical chains terminating the polymerisation reaction.
What is a common free radical producer
benzoyl peroxide which creates a benzoyloxy radical
What are condensation polymerisation
Condensation polymerisation occurs when a reaction between two molecules produces a larger molecule with the elimination or producing a smaller molecule.
What controls the properties of a polymer
- molecular structure of repeating units
- molecular weight and chain length
- Degree of chain branching
- cross linking
- filler or plasticizer (filler particles reduce shrinkage and increases strength - because filler particles don’t shrink and don’t react in polymerisation) —> (plasticizers are small monomers which don’t react with other monomers and they lubricate between the polymer chains to make it more malleable and flexible)
What are GICs
Glass Ionomer Materials
- a mixture of fluoro-alumino-silicate glass powder and a water-soluble polymer, primarily polyacrylic acid
- crosslinked polymer forming a 3D network which makes it more ridged, brittle and strong
- Weaker than resin composites
What chemical reaction does GICs use
cross linking and gelation reaction
What are positives of GICs
- Less technique and moist sensitive
- Bond directly to the tooth structure - however bonding strength isn’t as good as resin composite + bonding agent
- Release fluoride
- Good clinical performance when used correctly
What are negatives of GICs
- Relatively poor mechanical strength - not strong and can chip off especially on occlusal of molars - often replaced by resin composites
- Weak bonding to tooth structure
- Not the best for aesthetics
What is amalgam
Amalgam is a mix of different metals (silver tin, copper, zinc) which is mixed wither mercury. The mercury is dissolved by the mercury forming a crystal matrix.
