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Semester II - Dental Materials > Resin Based Composite Materials > Flashcards

Flashcards in Resin Based Composite Materials Deck (42)
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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

- 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



Is the Silane molecule biofunctional?


- 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


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?

1. Universal: Can be used for all applications but there may be some compromise in specific uses

2. Flowable: More fluid composites used especially for the ultraconservative restoration of teeth

3. 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