Composite Resins Flashcards
Under what conditions may a composite restoration be placed into a tooth? (4 points)
- New dental caries
- Abrasion/erosion
- Failed restoration/secondary caries
- Trauma
What are the 5 things contained within composite resins?
- Glass filler particles
- Resin
- Camphorquinone (photo initiator)
- Low weight dimethacrylates
- Silane coupling agent
The filler particles within amalgam can have various types of glass in them. What are 5 examples of these?
- Microfine silica
- Quartz
- Borosilicate glass
- Lithium aluminium silicate
- Barium aluminium silicate
What is the particle size and % volume for <i>conventional</i> composite resin filler particles?
Particle size = 10-40um
% volume = 50
What is the particle size and % volume for <i>Microfine</i> composite resin filler particles?
Particle size = 0.04-0.2um
% volume = 25%
What is the particle size and % volume for <i>Fine</i> composite resin filler particles?
Partical size = 0.5-3um
% volume = 60-70%
What is the particle size and % volume for <i>Hybrid</i> composite resin filler particles?
Particle size = Range (0.01-0.1um and 1-10um)
% volume = 70%
What monomers are used in the resin of composite resins? (2 examples)
- BIS-GMA - reaction product of bisphenol-A and glycidyl methacrylate
- Urethane dimethacrylates
What are the key characteristics of monomers in composite resins? (2 points)
- Difunctional molecule (essential for the cross linking that will be needed for the polymerisation reaction)
- Undergoes free radical addition polymerisation
What is Camphorquinone activated by?
- Blue light (curing light)
What type of molecules does Camphorquinone produce and what do they do?
- Produces radical molecules (that are electrically charged)
- These initiate free radical addition polymerisation of BIS-GMA which leads to chan ges in resin properties
Camphorquinone causes a degree of conversion of resin. What percentage or conversion can it facilitate?
- 35-80% (the rest is unreacted monomer)
Why are low weight dimethacrylates added to composite resins? (2 points)
- Added to adjust viscosity and reactivity
- Slows down the setting of the material
Why is a silane coupling agent used in composite resins? (3 points)
- Good bond between filler particle and resin is essential
- Normally water will adhere to glass filler particles, preventing resin from bonding to the glass surface
- A coupling agent is used to preferentially bond to the glass and also bond to the resin
What are 7 uses of composites?
- Where aesthetics are important
- Class III, IV and V permanent restorations
- Class II - limited occlusal wear
- LAbial veneers
- Inlays, onlays - indirect technique
- Cores
- Modified forms as luting cements (some dual cured)
How would you classify composites? (3 points)
- Filler type
- Curing method (light cured or self cured)
- Area of use:
- Anterior - microfilled, or submicron hybrid
- Posterior - Heavily filled
- Universal - Submicron hybrid
How can you classify a composite in terms of handling characteristics? (3points)
- Condensable
- Syringeable
- Flowable
What is meant by a condensable composite?
- ‘amalgam’ feeling - greater porosity
- (one that yo can pack into a cavity in a similar way to amalgam)
What are the characteristics of a syringeable composite? (3 points)
- good adaption, less porosities and easy to apply
What are the characteristics of a flowable composite? (4 points)
- Lower filler content
- More shrinkage
- Difficult to apply
- Place for them - with fibrous ribbons
What are the effects of adding filler particles to composite resins? (7 points)
- Improved mechanical properties
- Increased aesthetics
- Increased abrasion resistance (less easy to break the surface)
- Lower thermal expansion (still not perfect)
- Lower polymerisation shrinkage
- Less heat of polymerisation
- Some radiopaque
How many pastes are in a self curing composite?
2 pastes
How many pastes are in a UV activation composite resin?
one paste
How many pastes are in a light cure composite resin?
one paste
What happens in self cure composite activation?
Benzoyl peroxide + aromatic tertiary dentine -> free radicals
What happens in light cure composite activation?
Camphorquinone + blue light (430-490nm) -> free radicals
What are the advantages of light curing systems? (6 points)
- Extended working time i.e. on demand set
- Less finishing
- Immediate finishing
- Less waste
- Higher filler levels (not mixing two pastes)
- Less porosity (not mixing two pastes)
When light curing where is most of the light absorbed and what effect does this have?
- Most of blue light is absorbed close to the surface
- Composite resin nearest the surface sets the most readily and becomes hard
What is meant by the ‘ depth of cure’?
- The depth to which the composite resin polymerises sufficien tly (such thaqt its hardness is about half of that of the cured surface)
What is the typical depth of cure of a composite resin?
- 2mm
What does the depth of cure indicate to use when building a restoration?
- Indicates increment thickness to use
- Increment > 2mm results in a under-polymerised base which causes poor bonding to the tooth and early failure
What do bulk fill composites have as well a Camphorquinone?
- Lucerin initiator (requires UV light)
What is UV and blue light needed to polymerise bulk fill composite material fully
= As contains both Lucerin initiator and Camphorquinone which have different optical absorption spectrums
What lab test is used to test bulk filled composites?
- Curing light positioned at several points
- Use hardness tests to verify if material at 4mm depth has cured fully
What are the disadvantages for the lab test for bulk fill composites? (5 points)
- Can curing light be positioned the same as in a lab test
- Can optical rod be placed adjacent to tooth/composite
- Does all blue light illuminate material
- Will the composite polymerise fully
- What impact does ‘stray’ blue light have on soft tissue
What are the potential problems of using light cure? (5 points)
- Light/material mismatch - overexposure
- Premature polymerisation from dental lights - avoid exposure
- Optimistic ‘depth of cure’ values (use small increments - 2mm max)
- recommended setting time too short
- Polymerisation shrinkage - affects bond to tooth, potential for fracture or microleakage
What are the factors that could make a potential problem with setting times being too short? (5 points)
- Light used
- Light/material distance
- Contamination or damage to light guide
- Timer accuracy
- Variations in light output
What type of reaction is light curing?
- Exothermic
- Release of heat in resin material
- Heat conducts to adjacent enamel/dentine
What kind of light beam does light curing have?
- A divergent light beam
- Beams through transparent optical rod and then diverges
Modern light curing devices tend to be brighter/more intense. What is the theory behind this?
- Idea is more intensity accelerates curing, reducing the exposure duration needed
Unless the optical rod of a curing light is ALWAYS close to the composite resin, what may happen?
- SOME blue light may illuminated the patient’s soft tissues which may cause thermal trauma
What should you use with a curing light to prevent ocular damage?
- Use orange safety shields or glasses
Are composite resins typically strong and rigid?
- Yes
What are the requirements of a composite resin used for a large posterior cavity? (3 points)
- High strength
- High YM
- High abrasion resistance
What are the requirements of a composite resin used for a deciduous tooth with a large pulp? (3 points)
- Strong in thin section
- Wear = wear of tooth
- Other properties more important - bonding, microleakage
What are the properties of conventional composite resins?
- Strong but problems with finishing and training due to soft resins and hard particles
What are the properties of microfine composite resins? (2 points)
- Smaller particles - smoother surface better aesthetics for longer period
- But inferior mechanical properties (elastic limit and YM)
What do hybrid composite resins usually compromise between ?
- Originally compromisebetween conventional and microfine composites
What is meant by the term ‘hardness’?
- relates to materials surface and its resistance to scratching
- Indentation resistance
What is meant by the term ‘abrasion’?
- Removal of surface layers when two surfaces make frictional contact
What affects can surface roughness have? (3 points)
Affects:
- Appearance
- Plaque retention
- Sensation when in contact with tongue
What are examples of factors affecting wear (material factors)? (5 points)
- Filler material
- Particle size distribution
- Filler loading (% of filler that is there)
- Resin formulation
- Coupling agent
What are examples of factors affecting wear (clinical factors)? (6 points)
- Cavity size and design
- Tooth position
- Occlusion
- Placement technique
- Cure efficiency
- Finishing methods
What technique is used to bond composite to enamel?
- Acid etch technique
What system is used to bond composite to dentine?
- Dentine/universal bonding systems
What bond strength would you be expecting when bonding composite to dentine and enamel?
- 40MPa
What does good bonding of composite resins to tooth surfaces reduce? (3 points)
- Reduce microleakage
- Counteract polymerisation shrinkage
- Good bond will reduce the likelihood of a gap between the restoration and the tooth
Which is more resistant to abrasion: hybrid or microfilled composite?
- Hybrid composite
What is the elastic limit of a material?
- The amount of stress the material can take and still go back to its original shape
What is flexural strength?
- The material’s ability to bend without obtaining any major deformities
Which type of composite has a higher compressive strength: microfilled or hybrid?
- Hybrid
- 300MPa compared to 260MPa of microfilled
Which type of composite has a higher elastic limit: microfilled or hybrid?
- Hybrid
- 300MPa compared to 160MPa of microfilled
Which type of composite has a higher tensile strength: microfilled or hybrid?
- Hybrid
- 50MPa compared to 40MPa of microfilled
Which type of composite has a higher flexural strength: microfilled or hybrid?
- Hybrid
- 150MPa compares to 80MPa of microfilled
Which type of composite has a higher elastic modulus: microfilled or hybrid?
- Hybrid
- 14GPa compared to 6GPa
Which type of composite has a higher hardness: microfilled or hybrid?
- Hybrid
- 90VHN compared to 30VHN of microfilled
Is amalgam a better material than hybrid composite?
Yes, but not by much
What is the thermal conductivity of composite?
- Low - which is good
What is the thermal expansion coefficient of composite?
- High - which is poor
Why should thermal conductivity of composite be low?
- To avoid pulpal damage from hot and cold foods/fluids
Why should the thermal expansion of composite resin be equal to that of teeth?
To reduce microleakage and gap formation
What is the thermal expansion coefficient of composite resin?
- Composite = 25-68ppm/degrees celcius
- Enamel = 11
- Dentine = 8
Are composite resins radiopaque?
- Some of them are
What are important aesthetic properties for composite resins to have? (5 points)
- Shade range
- Translucency
- Maintenance of properties over lifetime
- Resistance to staining
- Surface finish
Are composites anticariogenic?
- Generally NO
- BUT a few products claim to release fluoride
Do composites have a high or low setting shrinkage?
- Low
- If minimise shrinkage then minimise the stress between the 2 tissues
- Bonding techniques and clinical techniques help to minimise the impact of this
What is the biocompatibility of composite resins?
- Generally thought to be okay but increasing concern about resins in general (NB not all monomer is polymerised)
When are you likely to place an RMGI? (2 points)
- High caries risk patients
- Frequent attenders
When are you likely to place a compomer? (3 points)
- Medium caries risk patient
- Caries under control
- Regular attenders
When are you likely to place a composite resin?
- Low caries risk patients
