Biomaterials Review: Composite Resin: week 2 Flashcards
Polymethylmethacrylate (PMMA), 1940’s
(4)
◦ Unfilled resin
- MMA resin mixed with PMMA polymer beads
◦ High polymerization shrinkage (7%),
◦ High thermal expansion (90 ppm/C)
- Marginal leakage
◦ Low strength
Composite Definition:
a physical mixture of 2 or more materials with
superior properties as compared to the individual components.
Composite examples
(4)
◦ Concrete: cement + gravel
◦ Fiberglass
◦ Dentin: collagen matrix + hydroxyapatite crystals
◦ Dental composites: Resin + Filler Particles
Dental Composite Uses
(5)
Tooth-colored restorative material
Bonding agents (filler may be present)
Sealants (filled)
Composite resin luting agents (cement)
Resin-modified glass ionomer material
Resin matrix phase reinforced by
dispersed filler particle phase bound to
the resin by a silane coupling agent
Resin matrix
◦ Bis-GMA, TEGDMA
Filler particles
(2)
◦ Quartz
◦ Colloidal silica
Activator-Initiator system
(2)
◦ Usually photoinitiator is what we use
◦ Camphorquinone (sensitive to 470 nm visible
light) (Yearn, 1985)
Dental Composite Components
(6)
◦ Resin matrix
◦ Filler particles
◦ Coupling agent
◦ Activator-Initiator system
◦ Polymerization inhibitors
◦ Optical modifiers
Bis-GMA:
bisphenol A diglycidyl methacrylate
◦ Matrix in most North American products
TEGDMA: triethyleneglycol dimethacrylate
(4)
◦ ~30% added to Bis-GMA or UDMA
◦ diluting agent/viscosity controller
- used to dilute the BisGMA (or UDMA), which is very viscous
◦ Too much TEGDMA will increase the amount of polymerization shrinkage
◦ Helps to promote extensive cross linking
- results in a matrix that is more resistant to degradation by solvents.
- TEGDMA is another difunctional monomer (has two reactive ends)
*UDMA:
urethane dimethacrylate
Methyl methacrylate:
Monofunctional, only 1
reactive end
Adding filler particles — strength
INCREASES
Adding filler particles — polymerization shrinkage
DECREASES
Basics of Fillers:
(3)
◦ The more filler, the better
◦ Composite resin should have at least 75% filler by weight
◦ The smaller the size of the filler, the better
Crystalline silica (quartz),
types (2)
Crystalline silica (quartz),
◦ Ba, Li, Al silicate glass
◦ Amorphous silica
Filler Particles
◦ Dispersed in
resin matrix
Filler Particles
Distribution varies depending on the material
(3)
◦ filler loading %, expressed by weight or by volume
◦ filler size
◦ filler
Filler Loading Fraction
Dental composites:
— wt% or
— vol%
50-85
30-70
Benefits of Filler Particles
(6)
1.Reinforcement of resin matrix:
◦ Increase hardness, strength, elastic modulus, and wear resistance
2.DECREASED polymerization shrinkage: ~10% to ~2%
3.DECREASED thermal expansion and contraction
1.Fillers don’t expand or contract
4.Improved workability, handling
5.DECREASED water sorption
6.INCREASED radiopacity (Barium, Strontium, Zirconium)
Filler Size Distribution
Good distribution necessary to
incorporate maximum amount of filler
Silane
(4)
◦ Couples filler to resin matrix
◦ Allows stress transfer from flexible matrix to higher modulus
(aka less flexible) filler particle
◦Improves the mechanical properties
◦ Decreased water sorption along filler-resin interface
Resin polymerization (free radical
addition reaction)
(4)
◦ Activation: Activator converts
initiator into a free radical
◦ Initiation: Free radical initiator
starts the addition reaction
◦ Propagation: continued polymer
chain growth
◦ Termination
Polymerization Inhibitor
(4)
Prevent spontaneous polymerization when dispensed
Stop polymerization from brief room light exposure (reacts with free
radicals)
Once the blue light is used, all inhibitor quickly consumed=
polymerization chain reaction starts.
Butylated hydroxytoluene (BHT)
Butylated hydroxytoluene (BHT)
◦ Food preservative, reduce oxidation
Optical Modifiers
Pigments:
metal oxides
Optical Modifiers
Opacifiers:
(4)
◦ Titanium and aluminum oxide
◦ Control opacity or translucency
◦ Brand differences
◦ Dentin vs enamel composite shades
Different ways to classify composites based on:
(3)
• Filler particle size and size distribution
• Handling characteristics
• Type of polymerization
Classification by Filler Size and Distribution
(4)
- Macrofill
- Midifill
- Microfill
- Hybrids
a. Midi-Micro Hybrid (Midi- or Microhybrid)
b. Mini-Micro Hybrid (Microhybrid)
c. Mini-Nano Hybrid (Nanohybrid)
Macrofill & Midifill Composites
NOT USED MUCH TODAY
10-100 m (macro)
1-10 m (midi)
65-70 wt%
Large fillers
◦ Rough surface finish
Not good size distribution
◦ Increased inter-filler resin space, low wear resistance
Prone to staining
Brands: Adaptic (macro)
Concise (midi), still on market
Microfill Composite
0.01-0.1 m particles, colloidal silica
40-60 wt%
◦ Due to large filler surface area, difficult to increase filler fraction, too viscous
Excellent finish, Best wear resistance of this generation
Weakest
Use for esthetic, low-stress sites
◦ Class III
◦ Layer over hybrid, kit systems
Brands: Durafill VS, Epic TMPT, Renamel, Heliomolar
Hybrid Composites
Midi-Micro Hybrid (First hybrids)
◦ Typically called Microhybrids
◦ Mix of midi and microfillers,
1-10 & 0.01-0.1 m
◦ 75-80 wt%
◦ Improved surface finish
compared to macro and midi composites
◦ High strength
◦ Many of the of current materials are hybrid
◦ Z250, Z100, Herculite, TPH, APH, Point 4
Mini-Micro Hybrid
a. Also called Microhybrids
b. Mix of mini and microfillers,
0.1-1 and 0.01-0.1 m
c. 80-85 wt%
d. Newer material
1) Smoother finish than midi-micro hybrid
2) Slightly lower strength
e.Clearfil APX, 4-Seasons, Miris, Vitalescence, Synergy, Tetric, EsthetX
Mini-Nano Hybrid (Nanohybrid)
◦ Nanometer: 10-9 Micrometer: 10-6
◦ Mix of mini, and nanofillers,
0.1-1 and 0.001-0.01 m (1-10 nm)
◦ ~80 wt%
◦ Newest materials: Filtek Supreme Ultra (what is used in clinic), Premise,
TPH3 (what you use in lab), Simile
◦ Strength comparable to microhybrids and finish
equivalent to microfills
◦ Not all “nanocomposites” contain nanofiller (<100
nm), filler size reported in nm,
i.e. 300 nm
Classification by Handling Characteristics (3)
Regular
Flowable
Bulk Fill
Flowable Composite
(3)
Low viscosity hybrid
Reduced filler,
40-60 wt%, adapts better without handling
40-60 wt%, adapts better without handling
(4)
◦ Lower filler percentage, decreased modulus, increased flexibility
◦ May be used under regular composite at gingival floor of Class II
◦ Thought may compensate for polymerization shrinkage stress and reduce gap
formation at gingival floor.
◦ However, research does not support theory.
Many are not radiopaque
◦ Big problem=
difficult to distinguish from recurrent caries
Flowable
shrinkage vs stress
◦ more shrinkage
◦ lower filled
◦ less stress
◦ has more resin to relieve the stress as it cures
◦ good in abraction areas
Hybrid
shrinkage vs stress
◦ less shrinkage
◦ higher filled
◦ more stress
Bulk fill
Newer technology- to avoid incremental placement
◦ One “bulk” placement
Need high output lights, at least 20 seconds
◦ ~ 1000 Mw/cm2
◦
Needed to cure through larger increments of material (up to 4-5mm)
Highly filled
◦ more translucent fillers
◦ which do not shrink
◦ = less resin matrix
◦ which does shrink
◦ Higher filled = more stress
◦ less resin to relieve the stress when it cures
Bulk fill
Classified by type:
(2)
Flowable BASE Bulk-fill
Full-body Bulk-fill
◦ Need more evidence to promote this use
Packable
Mini and midi fillers, >80 wt%
Supposed to handle like amalgam
◦ Marketed as amalgam alternatives
◦ Called “condensable,” but this is inaccurate
Conventional hybrids have superior properties
Bulk cure inadequate
P60, Surefil, Alert
Not well-accepted
Classification by Polymerization Activation
(3)
- Self-cure, chemical activator
- Light-cure, blue light activator
- Dual-cure, combination of both
Chemical or Self-cure Composite
2-paste system, 1 with activator, 1 with initiator
◦ Mixed to begin polymerization
Chemical or Self-cure Composite
Activator:
Initiator:
Aromatic tertiary amine
Benzoyl peroxide (BPO)
Chemical or Self-cure Composite
Advantage:
bulk placement
Chemical or Self-cure Composite
Disadvantages
(3)
◦ Mixing, incorporate bubbles, decrease strength
◦ No control of working time
◦ Amine, not color stable
Light-cure Composite
One-paste system
Light-cure Composite
Activator:
Blue light (~470 nm)
Light-cure Composite
Initiator:
(2)
◦ Camphorquinone (CQ), photoinitiator
◦ DMAEMA, alphiatic amine (accelerator)
Light-cure Composite
Advantages
(3)
a. Mixing not required, less porosity, increased
strength
b. Aliphatic amine (DMAEMA) more color stable
than self-cure aromatic tertiary amine
c. Better control of working time
Light-cure Composite
Disadvantages
(2)
a. Limited light penetration, ≤ 2mm increments, 20
sec
b. Blue light, retina damage – use orange shield
Light-cure Composite
Curing equipment factors:
(3)
◦ Bulb output, ≥ 300-400 mW/cm2
(11mm tip)
- At least 550 mW/cm2 for TPH3 or Filtek Supreme
- At least 1000 mW/cm2
for Bulk Fill
◦ Fiber-optic bundle breakage
◦ Tip contamination or damage
◦ Infection barrier
Light-cure Composite
Types of curing units:
(4)
- Quartz-tungsten-halogen
- Plasma Arc
- Laser
- Light-emitting diodes (LED)
Light-cure Variables
Procedural factors
(3)
◦ Exposure time
◦ Tip size: smaller tip= increase output, increase heat
◦ Distance: decrease Output when you increase
distance
Light-cure Variables
Restoration factors
(3)
◦ Darker shades absorb light
◦ Smaller particles: increase light scatter
◦ Curing through tooth
- decrease output
Curing Lights: Quartz tungsten halogen (QTH)
(4)
Usually tested with an 11 mm diameter light tip
◦ However, if a 3 mm diameter tip is used then the output can increase 8 fold which also can
heat up the tooth greater than the 5-8 degrees that can cause pulp cell death
Don’t touch the tip to the material being cured
At 6.0 mm distances from the restoration the output at the tip can be 1/3 what
it should be.
Never look directly at the light it can cause retinal damage.
Light Curing: equipment factors
Factors that reduce light output
(4)
◦ Frosting of bulb, Light reflector degradation, Fiber optic bundle breakage
◦ Tip contamination by resin buildup - lower output
◦ Sterilization problems - frosting the tip
◦ Infection control barriers - need longer curing times
Classified by Activation:
Dual-cure Composite
(2)
Both light and chemical activator/initiator systems present
Used under ceramic inlays, onlays, crowns
◦ Composite cement
◦ Accommodate thicker areas, light may not penetrate adequately
Oxygen inhibited layer
~15 microns thick, on the outer layer which facilitates addition and wetting of
subsequent layers
Just-cured composite may have –% of the unreacted methacrylate groups to
copolymerize with the newly added material
50
Older restorations –
will fully cure over time, do not have the unreacted
methacrylate groups
◦ Repair strength will be 50% of the original restoration. (Roughen with diamond)
Important Properties of Dental Composite
(7)
- Thermal expansion and contraction
- Sorption
- Surface finish
- Wear resistance
- Strength, elastic modulus
- Degree of Conversion
- Polymerization shrinkage
Properties: Thermal Expansion Coefficient
With temperature change, materials
expand and contract
(2)
◦ Larger mismatch between tooth and
restoration, margins debond, microleakage
◦ Filler: low TEC; More filler, less expansion
& contraction
Properties: Sorption
(3)
Water, saliva absorption, cause material to expand
Filler, silanation, and cross-linking the resin decrease sorption
Ideally want sorption to be ≤ 2%
Finish and Polish:
Obtaining anatomic contours of composite resin after
placement
Grinding –
gross cutting of excess material
Finishing –
fine cutting
Polishing -
final smoothing
◦ FINISH FIRST
Surface Finish:
Particle Size Effect and detachment from resin matrix
— best wear resistance
Microfill
◦ Related to small fillers and close filler spacing
Newer hybrid materials similar wear resistance to —
microfills
Additional Wear Factors:
(2)
◦ Maintain occlusal contacts on enamel
◦ Anterior < Premolars < Molars
Increased filler, increased —
strength
Microfill – Hybrids (all types)
<
◦ Microfill weakest, 40-60 wt% filler
◦ Often used over hybrid for optimum esthetic
surface
◦ Low stress areas
As filler increases, Modulus (stiffness) —
increases
: less flexible
Low modulus applications (abrasion lesions)
(2)
◦ Lower modulus of elasticity materials are better for Class V lesions because the tooth flexes.
◦ Microfill better here for class V lesions. A lower modulus material will flex a little and
compensate for flexural forces.
High modulus,
MOD restoration, minimize cusp flexure
Degree of Conversion (DC)
Measure of the % of carbon-carbon double bonds that have reacted
during polymerization reaction
The higher the DC, (3)
better strength, wear resistance, decreased sorption.
55-65% conversion
◦ With dimethacrylate system, does not mean that 40-50% of monomer
unreacted
At 20% conversion a — is created
gel
Polymerization Shrinkage
(3)
- Composite shrinks ~2% when it is cured
a. Filler effect – when fillers are added, shrinkage is reduced because fillers don’t shrink - Bis-GMA/TEGDMA Resin, ~10% shrinkage
- Linear vs ring-opening monomers
◦ Ring opening results in less shrinkage
(<1%)
With polymerization shrinkage, stress occurs at the composite-tooth
interface.
(2)
◦ Stress level will vary, depending on the type of restoration
configuration factor, C-factor
◦ C-factor = bonded/unbonded surfaces
Highest stress is Class – restoration (~13-17 Mpa)
I
Gap formed between adhesive and tooth
~ 5-20 microns
Managing Polymerization Shrinkage/Stress
(3)
Incremental placement
◦ decrease bonded/unbonded, each increment
◦ Reduces STRESS
◦ Shrinkage remains the same
Self-cure composite
◦ Slower polymerization rate
◦ Internal flow, compensates for shrinkage
Low shrinkage composite
◦ Filtek LS 0.9% shrinkage
◦ Silorane resin, ring opening
Resin matrix
(3)
◦ Polymerized resin is biocompatible
◦ Unpolymerized material (monomer) potentially cytotoxic, but poor
solubility
◦ Bis-phenol A, precursor of Bis-GMA is estrogenic
Bis-phenol A, precursor of Bis-GMA is estrogenic
(3)
◦ Fetal reproductive anomalies, decrease sperm count,
increase proliferation cancer cells with estrogen receptors
◦ Controversy, is BPA present in composites?
◦ Initial studies indicate this is not a concern, but need more long-term evaluation, better
technology. As little as 1PPT CAN affect fish reproductive organs.
Filler size
(2)
◦ Concern regarding the nanofillers and potential to cross cell
membranes
◦ Possible problem during restoration finishing and removal
Size of filler can be smaller than a —
virus
During finishing of composite
(3)
◦ finish under water spray and high-speed suction
◦ with a face mask on
◦ to avoid breathing the dust into yours and the patient’s lungs
Bonding Agent
Primer/Adhesive Resin
◦ Resin matrix phase, unfilled
◦ Flows into etched dentin and enamel, micromechanical union
◦ Macro and micro resin tags, enamel
◦ 1-5 micron thick hybrid layer, dentin
◦ Co-polymerizes with the composite material
◦ Chemical union
Chemistry game changer is 10-MDP Methacryloyoxy-decyl-dihydrogen-phosphate
Mechanism of action :
A monomer that chemically interacts via ionic bonding to calcium in
hydroxyapatite
10-MDP (3)
Single bottle, no mix adhesive system
Can be used in total etch, self-etch or selective-etch mode (etch enamel only with phosphoric
acid and rest of tooth with universal adhesive)
Monomer is a phosphate ester
Technique for Light-cured Composite
(8)
- Select shade prior to rubber dam
- Preparation (mechanical retention?) and caries removal
- Total Etch/2-step (1-bottle) adhesive:
a. Etch 15 sec, Rinse 10 sec
b. Blot excess water with brush or pellet
Do not overdry
c. Apply bond agent
a. Dry 5 sec, evaporate solvent without drying tooth - Light polymerize 20 sec (all areas cured)
- Place composite in ~2 mm increments
a. Increments should not span across entire prep, C-factor
b. the first increment next to the pulp about 1 mm thick)
c. Polymerize 20 sec; longer for darker shades or if curing through
the tooth
d. Protect material from extended exposure room and overhead
light, will cause a premature set
6.Minimize void formation
7.Cure longer when curing through the tooth - ie, curing the facial side of a distolingual restoration
8.Overfill slightly, allow material for contouring, finishing and
polishing
Fracture Toughness
(3)
Similar to flexural strength except a notch is placed at the bottom of the
sample
Good test for composite property
Test with a flaw in material – the way restorations and life really is
Glass Ionomer Materials
Many dental uses:
(5)
◦ Cements
◦ Liners and bases
◦ *Sealants
◦ Restorative materials
-Primarily Class V
◦ *Core buildup materials
Acid-base reaction, results in Fluoride release
(3)
◦ Initial “burst” of Fluoride released, then very low-level release
◦ This level does not protect teeth from caries
◦ Needs to be “recharged” with fluoride to continue releasing at adequate levels to be protective
Resin-Modified Glass Ionomer
Primary Use in Operative Dentistry:
Liner
◦ Vitrebond Plus
◦ Light cured
◦ Recommended when dentin is less than 2mm thick
◦ Liner layer should be no thicker than 0.5mm
Resin-Modified Glass Ionomer
(4)
◦ Use as Restorative material
◦ Dual Cure
◦Indicated for Root Caries
◦ Ex. Equia Forte
Polyacid Modified Composites
Compomers
(3)
◦ NO acid-base reaction with compomers
◦ This sets them apart from GI/RMGIs
◦ Ex. Geristore
