2/8: Composite Resins Flashcards
When was Silicate cement used?
1870s
What is silicate cement?
- high solubility
- severe surface wear
- low mechanical properties
When was polymethylmethacrylate (PMMA) used?
1940s
What is polymethylmethacrylate?
- initially unfilled: high curing shrinkage
-high thermal expansion and contraction - stress at the cavity margins (marginal leakage)
-Later, filler added (without coupling agent-no
bonded) = poor wear resistance and staining.
When was composite resin used?
1960s
What is composite resin?
- BisGMA
- fillers bonded (silane coupling agent)
*Improved properties: - low thermal coefficient of
expansion and dimensional change
on setting - higher wear resistance
- improved clinical performance
What is the definition of composite?
material containing at least two components (phases) with distinct chemical and physical properties that after blended, they show unique and superior properties as compared to the individual
components.
What are examples of composite?
Concrete: cement + gravel
Dentin: collagen matrix + hydroxyapatite crystals
Dental composites: Resin + Filler particles
What are tooth colored restorative materials?
composite resin, resin composite, composite
What is the resin matrix reinforced by?
dispersed filler particle phase bound to the resin by a silane coupling agent and an initiator-accelerator system
What are uses of composites?
- Tooth-colored restorative material (direct or indirect rest. technique)
- Bonding agents (filler may be present)
- Sealants (filled)
- Composite resin luting agents (cement)
- Resin-modified glass ionomer material
- Light-activated liner materials
- CAD/CAM blocks
- Resin endodontic sealers, etc.
How is dental composite packaged?
To protect against visible light (opaque) and moisture
* Plastic syringes
* Unit-dose capsules
* Dual paste syringes (dual curing – core build-ups)
What are components of composite?
- Resin matrix
- Filler particles
- Coupling agent
- Activator-initiator system
- Pigments and other components
What 3 things make up the resin matrix?
Bis-GMA
UDMA
TEGDMA
What are the filler particles of composite?
Crystalline silica (quartz), Ba, Li, Al silicate glass, amorphous silica
Where are filler particles disbursed and what does the distribution vary depending on?
- dispersed in resin matrix
- varies dependent on material (filler loading %, expressed by weight or volume & filler size/combination)
What are the benefits of filler particles?
Reinforcement of resin matrix
* Increase the mechanical and physical prop. (hardness,
strength, elastic modulus, and wear resistance)
DECREASED polymerization shrinkage
-The reduced shrinkage is proportional to the filler vollume
DECREASED thermal expansion and
contraction
* Higher filler amount reduces the thermal expansion
and contraction coefficients
Viscosity control
* Improved workability, handling
DECREASED water sorption
* Decreases the water sorption
INCREASED radiopacity
* Barium, Strontium, Zirconium
What does silane act as?
Interfacial bridge (strongly binds the filler to the resin matrix)
What are the benefits of silane as a coupling agent?
- Better stress distribution
between resin matrix and
filler particles - Improves the mechanical
properties - Decreased water sorption
along filler-resin interface
Describe composites as chemicals
Monomers to be converted into polymers
What is the process of activating and initiating triggered by?
Free radicals (Chemical activation, heat or light)
What is the activator and initiator of chemical or self-curing composite?
What is the activator and initiator of light-cured composite?
What do polymerization inhibitors prevent?
Spontaneous polymerization
What do polymerization inhibitors stop?
Polymerization from brief room light exposure (reacts with free radicals)
What happens once the blue light is used on composite?
All inhibitor quickly consumed = polymerization chain reaction starts
What chemicals increase the shelf-life of composite resins?
Butylated hydroxytoluene (BHT)
- food preservative, reduce oxidation
Hydroquinone
What are pigments of optical modifiers?
Metal oxides
What are opacifiers?
➢ Titanium and aluminum oxide
➢ Control opacity or translucency (enamel vs. dentin)
➢ Brand differences
What are the different classifications of composites?
✓ Filler particle size and size distribution
✓ Handling characteristics
✓ Type of polymerization
How can you classify composite by filler size and distribution?
- Macrofill
- Midifill
- Microfill
- Hybrids
a. Midi-Micro Hybrid (Midi- or Microhybrid)
b. Mini-Micro Hybrid (Microhybrid)
c. Mini-Nano Hybrid (Nanohybrid)
What kind of classification is not used much today?
Macrofill and midfill composites
What are macrofill and midfill composites?
✓ Large fillers (Rough surface finish)
✓ Fillers poorly distributed (Increased inter-filler resin space, low wear
resistance)
✓ Prone to staining
What are microfill composites?
✓ Excellent finish
✓ Low mechanical and surface properties (hardness)
✓ Use for esthetic, low-stress sites (Class III, Layer over hybrid, kit systems)
What are hybrid composites?
- mix of midi and microfillers
✓ Improved surface finish as compared to macro and midi composites
✓ High strength
✓ Universal composites (anterior and posterior)
Many of the of current materials are hybrid
What are mini-micro hybrid aka microhybrid composites?
Mix of mini and microfillers
Newer material
1) Smoother finish than midi-micro hybrid
2) Slightly lower strength
What are minni-nano hybrid composites aka naohybrids?
Mix of mini, and nanofillers
Newest materials
✓ Strength comparable to microhybrids and finish equivalent to microfills
What are the classifications by handling characteristics?
- Packable (conventional/regular)
- Flowable
- Bulk fill
What are the classifications of packable composite?
✓ Regular or conventional
✓ Medium viscosity
- Macrofill, microfill, hybrid, nanohybrid…
✓ Most widely used
What is flowable composite classified as?
Low viscosity - reduced filler content
Lower filler percentage, decreased modulus, increased flexibility
What is flowable composite used for?
Conventional composite at gingival floor of class II
- Thought may compensate for polymerization shrinkage stress and reduce gap formation at gingival floor.
What is flowable composite not?
Not Radiopaque
Why is the lack of radiopaqueness of flowable composite a problem?
Difficult to distinguish from recurrent caries
What is the point of bulk fill composite?
- To avoid incremental placement (“one bulk placement”)
✓ Highly filled with pre-polymerized particles
✓ Larger size fillers (reduces the light scattering)
✓ more translucent filler particles (increases the light penetration and polymerization)
✓ 5 mm increments
What kind of lights are used for bulk fill?
High output lights
What is condensable composite?
- Packable with high viscosity
✓ Mini and midi fillers, >80 wt%
✓ Supposed to be handled like amalgam (amalgam alternatives in the market)
✓ Bulk cure inadequate
What kind of composite is not well accepted? Why?
Condensable composite
- fractures at marginal ridges, changes on surface texture and color match
Rank the types of composite from high to low viscosity
What are the three classifications of polymerization activation?
- Chemical cure
- Light cure
- Dual cure
What is the activator and initiator of chemical cure composite?
Activator: Aromatic tertiary amine
Initiator: Benzoyl peroxide (BPO)
What are the advantages and disadvantages of chemical cure?
Advantage: bulk placement
Disadvantages: Mixing (incorporate bubbles, decrease strength);
No control of working time; Amine (not color stable)
What is the activator and initiator of light cure composite?
Activator: Blue light
Initiator: Camphorquinone (photosensitive ~470 nm) and DMAEMA
(accelerator)
What are the advantages and disadvantages of light cure?
Advantages:
-Mixing not required, less porosity, increased strength.
-Aliphatic amine (DMAEMA) more color stable than self-cure aromatic
tertiary amine
-Better control of working time
Disadvantages:
-Limited light penetration
- ≤ 2mm increments, 20 sec
-Blue light, retina damage – use orange shield
What are the four steps of reaction of polymerization?
- Activation
- Initiation
- Propagation
- Termination
What are procedural factors of light-cure variables?
-Exposure time
-Tip size: smaller tip= increase output, increase heat
-Distance: decrease Output when you increase distance
What are clinical factors of light cure composite?
-Darker shades absorb light – affect light penetration
-Smaller filler particles: increase light scatter
-Curing through tooth decrease output
What are types of curing units?
- Quartz-tungsten-halogen
- Plasma Arc
- Laser
- Light-emitting diodes (LED)
What is the quartz tungsten halogen light system?
QTH source consists of a tungsten filament that is surrounded by a clear, crystalline quartz bulb containing a
chlorine-based halogen gas
What kind of emission does the quartz tungsten halogen light system use?
Broad emission spectrum
What are characteristics of the quartz tungsten halogen light system?
- Cooling system is noisy
- Relatively low irradiance (increase exposure between 30 to 60 s to polymerize 2-mm-
thick of composite resin) - Heating in the output (pulp cell damage) – don’t touch the tip
- Retinal damage (Never look directly at the light)
What kind of emission do plasma-arc light (PAC) systems use?
Broad emission spectrum (390 to 510 nm)
High radiant power and high irradiance (to cure 2-mm thick composite resin in 3 to 5 s)
What are characteristics of plasma-arc light (PAC) systems?
- expensive
- Noisy, large, not portable, cannot be battery operated
- Become less popular with the introduction of LED curing lights
What are characteristics of the argon-ion laser?
✓ High irradiance in only 10 seconds (could rapidly cure dental resins)
✓ Produces several intense and narrow emission peaks
✓ Argon-Ion Lasers are expensive
✓ Become less popular with the introduction of LED curing lights
What are advantages of the light-emitting diodes (LED)?
- solid state, lightweight, battery driven
- more efficient (at least 10 times more than QTH)
-extremely long working life
What are factors reducing output?
- Degradation (light reflector, fiber optic bundle, bulb)
- Tip contamination by resin buildup - lower output
- Sterilization problems - frosting the tip
- Infection control barriers - need longer curing times
What is the oxygen inhibited layer?
~15 microns thick, on the outer layer which facilitates addition and wetting of subsequent layers
What are deficient polymerization problems?
What are important properties of dental composite?
- Polymerization shrinkage and stress
- Wear resistance
- Surface finish
- Marginal infiltration
- Water Sorption
- Radiopacity
- Color stability
What does polymerization yield?
Shrinkage
Consequently, stress occurs at the composite-tooth interface
✓ Stress level will vary, depending on the type of restoration
configuration factor, C-factor
What is C factor?
Bonded/unbonded surfaces
What happens with higher c-factor?
Higher stress
What is failure at the interface reduced by?
Reduced by effective bonding and lower c-factor
Higher filler amount =
Higher wear resistance
Lower filler size =
Higher surface finish
What is marginal infiltration?
✓ Decreased with improvement of adhesive systems
✓ Failure “gap” between tooth and composite
✓ Secondary caries, marginal staining and fracture, post-operative sensitivity
What is water sorption?
✓ Lower filler amount, higher water sorption = higher expansion
✓ BisGMA and TEGDMA: higher sorption as compared to UDMA
What is radiopacity important for?
Distinguish carious tissue and marginal adaptation, air bubbles (defects)
What are adhesive systems for bonding agents?
agents that bond micromechanically
or/and chemically the restorative material (or luting
agent) to tooth substrate through an interface
What does acid etching do?
◦ To remove the minerals from dental substrate
(micro-retentions on enamel and exposing the
collagen matrix)
◦ Allowing the adhesive infiltration
What is the mechanism of action of universal adhesives chemical bonding?
A phosphate
monomer that chemically interacts via ionic
bonding to calcium in hydroxyapatite
What are the steps of the bonding procedure at UMKC?
- Acid etch
- Rinse
- Vivapen
- Light cure for 10 sec
- Place resin
