Resin Based Composite Materials Flashcards
What is a Composite Material?
- Material made from 2 or ore constituent materials with significantly different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components
What is Resin based Composite?
- Composed of a chemically active resin and an inorganic filler bound together by a silane coupling agent
- Other chemicals are also present
Resin based Composites: What’s the resin components principle monomer?
- Traditionally. main resin component is based on:
Bisphenol A
Glycidyl methacrylate
= bis-GMA
” Bowen’s resin”
What’s the viscosity of bis-GMA?
- Long chain monomer with methacrylate group at either end of an aromatic spine
- Highly viscous
- Cannot be manipulated clinically
Resin Component: What’s a Diluent monomer?
- Viscosity controllers
- Lower molecular weight monomers which are required to permit clinical handling and proper mixing with the inorganic components
Examples of Diluent monomers are?
- Methylmethacrylate (MMA)
- Ethylene glycol dimethacrylate (EGDM)
If resin as used alone, what would the material exhibit?
- High strinkage
- Inadequate wear
- Increased exothermic reaction
- Poor mechanical properties
- No radiopacity
- Inorganic filer is incorporated into the system to compensate
What are the benefits of adding a filler component?
- Increases strength
- Increased wear resistance
- Reduced polymerisation shrinkage (decreases micro-leakage)
- Radiopacity via the addition of heavy metals
What are the classifications of resin composites?
Filer type:
- Gasses
- Ceramics
What are Glass fillers?
- Amorphous solid material
Quartz:
- Silicon dioxide
- Fine particle
- Neither opaque or radioopaque
Silica-based glasses:
- Barium-aluminium silicate glass
- Fine particle
- Radiopque
What are the features of glass fillers?
- Quartz is the hardest
- Silicate glasses contain barium but are slightly softer and degrade very slowly when exposed to water
- Barium, Strontium and lithium are easy to finish
What are Macrofilled Composites?
- Large filler particle size
- Range from 15-35μm
- Large particles can support higher loads due to lower surface area to volume ratio - however you can’t pack as much in
- Difficult to finish and polish to an acceptable level - becomes rough quickly - plaque retention site and poor wear resistance
What are Fine particle Composites?
- Small particle size leading to better packing of filler and the reductin in the inter-particular distance filled with resin
- Reduction to wear
- More spherical particles means better finish and smoother surface
- Enhanced mechanical properties
What are Hybrid Composites?
- Contains particles of various sizes
- Theoretically has the benefits of both micro and macrofilled resin composites
- High filler density as the particles fit like a mosaic
What are Nanofilled Composites?
- Discrete non-agglomerated and non-aggregated particles between 20-70 nanometers
- Nanoparticles coalesce into Nanocluster fillers
- These Nanoclusters act as a single unit enabling high filler loading and strength
- Strength of a hybrid material but easier to polish
What happens to the composite when you add filler/when the filler load increases?
- Increasing the filler load is to make the mechanical properties of the resin composite closer to the filler
- Increasing the compression strength BUT increases brittleness
- Wear resistance increases but surface breakdown can occur if too much filler is added as there will be less resin to hold it together
- Too much filler increases stiffness - poor manipulation
What is a Silane Coupler used for?
- To bond the resin and filler (i.e. glass/ceramic) together
- Surface of the filler particles must be chemically coated to facilitate their bonding with the chemically active resin
- y-MPTS is a VINYL SILANE COMPOUND
Is the Silane molecule biofunctional?
YES
- Has a group which reacts with the inorganic filler (hydrophilic groups)
- Another group reacts with the organic resin (hydrophobic groups)
What are the repercussions of adding a Silane Coupler?
- Stress concentrations occur at the interface between the filler and resin forming crack initiation sites
- Stress transferred from the strong filler particles to the next though the low strength resin… can give in
How do you cure a Resin Composite?
- Light
- Chemical
- Dual (light and chemical)
How does the Chemical cure process work?
- Typically a two-paste system
- Settings reaction commences when the 2 pastes are blended (but you’ll never get 100% mix/reaction)
How does the Light curing process work?
- Use of a photo-initiator and a accelerator
- Peroxidase
- Diketone
- Lucirin TPO
- Accelerator is a tertiary amine
Why is an ultraviolet stabiliser needed?
- The material colour will change when exposed to natural light due to OXIDATION
- Prevented by the addition of an ultrviolet absorber such as
2-hydroxy-4-methoxybenzophenone
How does the ultraviolet stabiliser work?
Absorbs electromagnetic radiation
What polymerisation/curing inhibitors used for?
- Polymerisation is the conversion of monomers to polymers (curing)
- Monomethyl ether of hydroquinone is added to the resin composite to:
+ Prevent premature setting
+ Increase the matieral’s shelf-life
Why do we add a radiopaque material to the composite?
- Restorative materials need to be radiopaque in order to see them on an X-ray and identify secondary caries
- Add heavy metals like barium
- Radiodensity will vary depending on volume of radiopaque filler used
What’s the significance of adding pigment to the resin composite mixture?
- The materials optic properties should exactly match the tooth being restored
- Inorganic oxide compounds are added to the resin in small quantities
What’s Polymerisation shrinkage?
- Most important shortcoming on the curing process
- If a lot of shrinkage occurs there will be a gap left at the tooth/restoration interface leading to microleakage
- Microleakage of debris and microorganisms though the space will undermine the restoration and tooth leading to secondary caries
What are the effects of Polymerisation shrinkage stress?
- High levels of stress can be built up within the tooth causing bulk or microfracture of the tooth tissue
- Debonding of the restoration
- Bulk or microfracture of the restorative material
How can the placement of composite minimise polymerisation shrinkage stress?
- Configuration factor (C factor) ratio of bonded to unbonded surfaces
Higher the ratio the more stress is potentially incorporated into the situation
How should you place a composite filling to minimise Poly.shrinkage stress?
- Layer it up/incremental build-up
- With each cured increment shrinkage is minimised and compensated for to some extend
Why is the compliance of the tooth important for placing a restoration?
- ability of the tooth to withstand flexure
- Dependent on:
+ Amount of remaining tooth tissue
+ Quality of remaining tooth tissue
+ Position of remaining tooth tissue
Why should you be aware of ambient light?
- Resin composite is photophilic and ambient light can set it
- Strength and amount of ambient light in the clinical can prematurely set the material which is clinically detrimental
- Angle operating light away
What is the oxygen inhibition layer in reference to resin composites?
- Composite won’t fully cure in air; surface remains tacky with inferior mechanical properties
- Partly cured layer should be removed and the restoration trimmed back to remove this layer (i.e. polish the composite with composite finishing burs) OR
- Create an anaerobic environment covering with glycerine or dentine bonding agent
Why should you make sure the working environment is devoid of water?
- All resin-based composites are inherently hydrophobic
- Water can be taken up by the dental materials causing irreversible degradation of properties of the resin composite
What’s Hygroscopic expansion?
- Material swelling with water sorption
- Starts 15 minutes after initial polymerisation and continues for up to 10 weeks
What’s coefficient of thermal expansion?
- Resin composites have a coefficient of thermal expansion similar to tooth tissue
- Expansion is greatest with those resin composites that have a large volume fraction of resin
- Tooth/restoration interface is stressed during thermal cycling as restoration shrinks or expands more than the tooth - can cause microleakage - and compresses the tooth tissue which it is in contact with
What are the advantages of resin composites?
- Superior aesthetics
- More conservative cavities
- Command set
- Can be repaired adequately
- Lower microleakage compared to amalgam
What are the disadvantages of resin composites?
- Time consuming to place
- Expensive
- Hydrophobic
- Photophilic
- Polymerisation shrinkage
- Technique sensitive
- Difficult to finish adequately
What are the 3 groups of Resin Composites based on their handling characteristics?
- Universal: Can be used for all applications but there may be some compromise in specific uses
- Flowable: More fluid composites used especially for the ultraconservative restoration of teeth
- Packable: More viscous materials generally only used in posterior situations
If a material has a high filler content, how does it effect its stiffness?
- Stiff materials is related to a higher filler loading
- Low filler amount lower viscosity
What’s Universal Resin composite?
- Performs satisfactorily in many situations and often provides a clinically acceptable look
- Optic properties limit their application in specialist practice where more complex and challenging aesthetic treatments are being carried out
