Overview of Biomaterials- Amalgam and Intro to Composite Flashcards
Any substance, other than a drug, that can be used to treat,
augment, or replace any tissue, organ, or function of the body is a
biomaterial
•All dental materials which involve exposure to patients are
considered
biomaterials
4 Major Classes of Dental Materials
Metals and Alloys
Porcelains and Ceramics
Polymers
Composites
Polymers (2)
◦ Elastomeric (impression materials)
◦ Plastics (denture base, sealants)
Composites (1)
◦ Polymers with fillers
American Dental Association specifications (2)
◦ More than 10 specifications for dental materials, instruments, and equipment
◦ Restorative material specifications: related to material properties that should reflect clinical function
Restorative material specifications: related to material properties that should reflect clinical function (3)
◦ In vitro (in glass)- tested in the laboratory
◦ In vivo (in the living being)
◦ Extrapolation of in vitro data to in vivo conditions should be done with caution
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Food and Drug Administration (4)
◦ Safety, Efficacy
◦ Protect the public from hazardous or ineffective medical materials and devices
◦ 2009 FDA reclassification
◦ Direct to Consumer Orthodontics?
2009 FDA reclassification (3)
◦ Reclassified amalgam from class I to class II
◦ Class I: lowest risk à Class III: highest risk
◦ Same as composites, crown and bridge alloys
Performance of all dental materials depends on their
atomic structure
Atomic structure determines (2) of materials
mechanical and physical properties
Types of interatomic bonds (2)
◦ Primary: Ionic, covalent, metallic
◦ Secondary: Hydrogen bonds, Van der Waals force
Primary Bonds: Ionic
Electrostatic attraction of positive and negative charges
Primary Bonds: Ionic
Involves — — between ions
electron transfer
◦ One becomes positive, one becomes negative ex. NaF)
Primary Bonds: Ionic
Properties (2)
◦ non-directional, strong bonds (100-200kcal/mole)
◦ No free electrons, good thermal and electrical insulator
Primary Bonds: Ionic examples (2)
◦ Ceramics, gypsum
Primary Bonds: Covalent
2 atoms share an electron
Primary Bonds: Covalent
Properties (3)
◦ Directional bonds (50-100kcal/mole)
◦ Low electrical and thermal conductivity
◦ Water insoluble
Primary Bonds: Covalent
Examples (4)
◦ Water, glass, polymers, composite
Primary Bonds: Metallic
Cluster of positive metal ions surrounded by a gas of electrons
Primary Bonds: Metallic
Properties (2)
◦ Non-directional bonds (100 kcal/mole)
◦ High electrical and thermal conductivity
Primary Bonds: Metallic
Examples (2)
◦ Amalgam and gold alloys
Classification of Material Properties (4)
Biological
Surface
Physical
Mechanical
Biological Properties
The biological response to a material when in contact with the human body
Biological Properties
Dental examples: (3)
◦ Allergies
◦ Pulp response
◦ Gingivitis, inflammation
Surface Properties
The unique properties of a material associated with its surface
Surface PropertiesExamples
Surface energy/tension; surface wetting
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Dental examples of importance of surface wetting (6)
◦ Making and pouring impressions ◦ Investing and casting ◦ Tooth pellicle ◦ Denture retention ◦ Fluoride treatment ◦ Adhesive bonding
Physical Properties
Depend on
the type of atoms and the bonding present in material
Physical Properties
Size/Shape Effect
no effect
-structure insensitive
Physical Properties
Examples (3)
◦ Optical (color, translucency, gloss)
◦ Electrochemical: Tarnish, Corrosion
◦ Thermal: Conductivity, Diffusivity, Coefficient of thermal expansion
Thermal conductivity
◦ Quantity of heat passing through 1cm thickness of material
Thermal diffusivity
◦ How quickly crown interior approaches temperature of exterior
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Thermal Expansion Coefficient
(α)(20-50°C)
Α= final length-original length
original length x (*C final - *C original)
Mechanical Properties
Reaction of a material to the application of an external force
Mechanical Properties
Size/Shape effect
Size and shape of specimen affect properties
◦ Structure sensitive
Mechanical Properties
Applied force referred to as —
load
Stress
When load (force) applied to material, STRESS develops in response
Stress=
Load per unit area
◦ Measured in psi, MPa, kg/cm2
Fracture Stress- Strength
There is a limit to how much force a material can withstand before it breaks
Strength of material=
stress at fracture
Type of strength measured is dependent on
type of force applied
Types of Force/Stress (5)
Tensile Compressive Torsion Shear Flexure
Tensile Strength- PULLING force
Measure of the stress necessary to fracture a material by 2
opposing forces directed away from each other
Lowest strength for most materials
Tensile Strength- PULLING force
Tension pulls the
atoms and structure apart
◦ Failure occurs at lower loads
Highest strength measure for most materials
Compressive Strength- PUSHING force
Compressive Strength- PUSHING force
Measure of the stress necessary to fracture a material by 2 opposing forces directed toward each other
Compression pushes
atoms and structure closer
◦ Usually require higher loads to cause failure
Torsion Strength- TWISTING force (4)
Not relevant to direct or indirect dental restorations Torque wrench (torsion) used to place dental implants Torsion test of experimental dental implant-bone interface stability/strength of osseointegration Torsional fatigue of endodontic rotary files
Shear Strength- SLIDING force (3)
Typically, intermediate strength between compressive and tensile
Stress necessary to rupture a material by 2 opposing parallel forces directed
toward each other but not in the same plane
Clinical situation with shear force/shear strength- implant bone interface
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Shear stress/strength at implant-bone interface (2)
Cylinder (press fit) implants: high shear
Threaded implants
skipped Threaded implants (2)
◦ Compressive stress below each thread (More ideal bone loading)
◦ Tension above thread, often see bone loss to level of 1st thread
Flexural Strength- BENDING force (2)
Measure of stress to cause failure in bending
Flexural stress/strength relevant in numerous clinical situations
3-point Bend test (2)
◦ Compressive load
◦ Combination of compressive & tensile stress
Flexural strength is vital due to occlusal load (3)
◦ On direct restorations (Amalgam and composite)
◦ Indirect restorations (Bridges/FDPs, single crowns, onlays)
◦ Removable prosthodontics (Palatal flex in maxillary denture)
Examples of DENTAL STRESS (2)
Protrusive movement
Posterior occlusion
Protrusive movement (2)
◦ Anterior teeth
◦ Flexure load on incisors
Posterior occlusion (3)
◦ Chewing = compressive load
◦ At marginal ridge contact areas
◦ At fossa areas
Occlusal Stress=
Occlusal load (force)/ Occlusal contact area
TRIPODIZED occlusal contacts
◦ Allows distribution of occlusal load across
maximum area
◦ = minimized stress
Premature contact results in decreased —
AREA
Premature contact results in decreased AREA
occlusal force? occlusal stress?
◦ Patient’s occlusal force stays the same
◦ BUT OCCLUSAL STRESS IS INCREASED
BUT OCCLUSAL STRESS IS INCREASED (2)
◦ Potential restoration failure
◦ Potential pain/discomfort for patient on biting
Strain
The DEFORMATION that occurs in a material when force is
applied to the material
Strain=
change in length (deformation)/
unit original length
how are stress and strain interrelated?
◦ If you have one, you will have the other
ELASTIC Strain
The TEMPORARY distortion of a material by applied force
elastin strain:
Strain is BELOW THE
ELASTIC LIMIT
elastic strain:
When force is removed, materials
reverts to original form
◦ Ex. Rubber band
PLASTIC Strain
PERMANENT distortion of a material
plastic strain:
Strain is
BEYOND the elastic limit
◦ Elastic portion of strain recovered
◦ Plastic portion of strain NOT recovered
plastic strain:
When force is removed, shape
remains changed
◦ Ex: bending a paper clip
Many benefits to amalgam: (4)
Easy to manipulate
Can be placed in its plastic state and carved before it hardens
Excellent physical properties
Cost effective (Including time to place)
Excellent physical properties (4)
◦ Strong and predictable
◦ Self-sealing
◦ Due to corrosion over time
◦ = effective barrier against recurrent caries
Amalgam composition: Kerr Contour Amalgam: Ag --% Sn --% Cu: --% --% spherical, --% lathe cut
41
31
28
70
30
Amalgam- Composition
In capsule with powder, mixed with
liquid mercury in triturator
Conventional Amalgam (2)
◦ Similar to G.V. Black’s original formula
◦ “low copper”
High Copper Amalgam (3)
◦ Contain 9-30% copper
◦ Superior to conventional
◦ Presence of copper nearly eliminates gamma-2 phase, resulting in stronger restoration
Phases of amalgam setting: (3)
Gamma
Gamma 1
Gamma 2
Gamma
◦ Tin and silver react with mercury, forms silver-mercury (gamma-1) and tin-mercury (gamma-2)
◦ Strong, corrosion resistant
Gamma-1
◦ Silver-mercury
◦ Weaker, susceptible to corrosion
Gamma-2
◦ Tin-mercury
◦ Weakest, most susceptible to corrosion
Add Copper=
creates a copper-tin phase (eta), eliminates tin-mercury gamma-2 phase
Lathe (2)
◦ Outdated- particles formed by cutting block of alloy with a lathe
◦ Resulted in large, irregular particles
Admixed (4)
◦ Lathe type particles mixed with small spheres
◦ Require more condensation force
◦ Most commonly used type of amalgam
◦ Low early strength (1-hour)
Spherical (4)
◦ Spherical shape
◦ Higher early strength (1-hour) and higher 24-hour strength than Admixed
◦ May be more difficult to achieve interproximal contact
◦ Require less condensation force
•Mercury to Alloy ratio (4)
- Less mercury in final restoration is superior
- Better strength and corrosion resistance
- Proper condensation and finishing results in less mercury in final restoration
- Admixed alloys ~50% mercury, Spherical alloys slightly less
•Trituration (3)
- Mixing the amalgam
- Longer and faster trituration= sets faster
- Follow manufacturer’s guidelines
•Condensation (2)
- Most critical variable
* Undercondensation is the most common error made by dentists
•Carving and Finishing (1)
• Pre-carve and post-carve burnish recommended with high copper alloys
Overwhelming evidence that supports the safety of amalgam (3)
◦ Mercury vapor is released in chewing
◦ No side effects at such low doses (Such as those from having amalgam restorations in your mouth)
◦ Dental Professionals exposed to more mercury vapor than non-dental professionals (Would expect more adverse health affects due to exposure, but that is not the case)
Most of the “data” that suggests amalgam is
unsafe is anecdotal
◦ (Looks like they’re going after root canal treatment now)
Amalgam has not been found to play a role in — diseases
neurodegenerative
Why not remove amalgam due to mercury concerns? (3)
◦ Unwarranted loss of tooth structure
◦ Unnecessary expense
◦ Limited longevity when replaced with inappropriate tooth colored restoration
Ways to classify composites (3)
◦ *Filler
◦ Handling
◦ Activation
Curing-
lights and methods
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History of Tooth-colored Materials
Silicate cement, 1870’s, high solubility Polymethyl methacrylate (PMMA), 1940’s ◦ Unfilled resin ◦ MMA resin mixed with PMMA polymer beads ◦ High polymerization shrinkage (7%), High thermal expansion (90 ppm/°C) ◦ Marginal leakage ◦ Low strength Composite resin, 1960’s
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 or Fibers
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
Dental Composite:
— colored restorative material
Resin matrix phase reinforced by —
May be referred to as: (4)
Tooth
dispersed filler particle phase bound to the resin by a silane coupling agent
composite resin, resin composite, composite
Dental Composite Components (6)
a. Resin matrix- Bis-GMA, TEGDMA
b. Filler particles - (Quartz, colloidal
silica)
c. Coupling agent
d. Activator-Initiator systemPhotoinitiator-camphorquinone
(sensitive to 470 nm visible light)
(Yearn, 1985)
e. Polymerization inhibitors
f. Optical modifiers
Bis-GMA:
bisphenol A diglycidyl methacrylate
◦ Matrix in US products
TEGDMA: triethyleneglycol dimethacrylate (3)
◦ ~30% added to Bis-GMA or UDMA
◦ diluting agent
◦ used to dilute the BisGMA and UDMA, which is very viscous
Too much TEGDMA will however increase the amount of
polymerization shrinkage. Helps to promote
extensive cross linking and results in a matrix that is more resistant to degradation by solvents. TEGDMA
is another difunctional monomer.
UDMA:
urethane dimethacrylate
◦ Matrix in European products, instead of Bis-GMA
Filler Particles
Crystalline silica (quartz), Ba, Li, Al silicate glass, amorphous silica
Filler Particles are dispersed in
resin matrix
Filler Particles distribution varies depending on the
material
◦ filler loading %, expressed by weight or by volume
◦ filler size, and
◦ filler
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 rxn) ◦ Activation: ◦ Initiation: ◦ Propagation: ◦ Termination
◦ Activation: Activator converts initiator into a free radical
◦ Initiation: Free radical initiator starts the addition reaction
◦ Propagation: continued polymer chain growth
◦ Termination
Polymerization Inhibitor
Prevent
spontaneous polymerization when dispensed
Polymerization Inhibitor
Stop polymerization from
brief room light exposure (reacts with free
radicals)
Polymerization Inhibitor
Once the blue light is used,
all inhibitor quickly consumed= polymerization
chain reaction starts.
Butylated hydroxytoluene (BHT)
◦ Food preservative, reduce oxidation
Pigments:
metal oxides
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
- Hybrids (3)
a. Midi-Micro Hybrid (Midi- or Microhybrid)
b. Mini-Micro Hybrid (Microhybrid)
c. Mini-Nano Hybrid (Nanohybrid)
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Macrofill & Midifill Composites
NOT USED MUCH TODAY 10-100 µm (macro) 1-10 µm (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
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Microfill Composite
0.01-0.1 µm particles, colloidal silica 40-60 wt% ◦ Due to large filler surface area, difficult to increase filler fraction, too viscous Excellent finish, Best wear resistance Weakest Use for esthetic, low-stress sites ◦ Class III ◦ Layer over hybrid, kit systems Brands: Durafill VS, Epic TMPT, Renamel, Heliomolar
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Hybrid Composites
Midi-Micro Hybrid (First hybrids) ◦ Typically called Microhybrids ◦ Mix of midi and microfillers, 1-10 & 0.01-0.1 µm ◦ 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
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Mini-Micro Hybrid
a. Also called Microhybrids
b. Mix of mini and microfillers,
0. 1-1 and 0.01-0.1 µm
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
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Mini-Nano Hybrid (Nanohybrid)
◦ Nanometer: 10-9 Micrometer: 10-6
◦ Mix of mini, and nanofillers,
0.1-1 and 0.001-0.01 µm (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 (2)
- Flowable
2. Packable
Flowable Composite
Low viscosity hybrid
reduced filler,
40-60 wt%, adapts better without handling ◦ Lower filler percentage, decreased modulus, increased flexibility
◦ Used under conventional 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
Many are not radiopaque
◦ Big problem=
difficult to distinguish from recurrent
caries
RADIOPACITY
Distinguish between
composite and recurrent caries
Barium, strontium, zirconium filler
Flowable vs Hybrid
handling characteristic
filler characteristic
Flowable (2)
◦ more shrinkage (is lower filled)
◦ less stress (has more resin to relieve the stress as it cures)
Hybrid (2)
◦ less shrinkage (is higher filled)
◦ more stress
skipped Bulk fill Newer technology- Need high output lights ~ Are highly filled with...
bulk fill
1000 Mw/cm2
more translucent fillers (which do not shrink) and less resin matrix (which shrinks)
◦ Higher filled have more stress because there is less resin to relieve the stress when it cures
Classification by Polymerization
Activation (3)
- Self-cure, chemical activator
- Light-cure, blue light activator
- Dual-cure, combination of both
Light-cure Composite
One-paste system Activator: Blue light (~470 nm) Initiator: ◦ 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
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Curing equipment factors (4)
◦ Bulb output, ≥ 300-400 mW/cm2 (11mm tip)
(Not below 300 mW/cm2, Not below 550 mW/cm2 for TPH3 or Filtek Supreme)
◦ Fiber-optic bundle breakage
◦ Tip contamination or damage
◦ Infection barrier
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)
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Curing Lights: Quartz tungsten halogen
(QTH)
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.
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Curing Lights: QTH– soft start or ramp cure
Starts low intensity, intensity increases
over time of cure
The theory is that a soft cure can allow
some stresses to be relieved in the
composite resin before it reaches the gel
stage; forms stronger long-chain polymers, decreases polymerization shrinkage
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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 time
Classified by Activation:
Dual-cure Composite (4)
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 50% of the unreacted methacrylate groups to copolymerize
with the newly added material
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)
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Important Properties of Dental
Composite (7)
- Thermal expansion and contraction
- Sorption
- Surface finish
- Wear resistance
- Strength, elastic modulus
- Degree of Conversion
- Polymerization shrinkage
With polymerization shrinkage, stress occurs at the composite-tooth
interface. (3)
◦ Stress level will vary, depending on the type of restoration
configuration factor, C-factor
◦ C-factor = bonded/unbonded surfaces
Highest stress is Class I restoration (~13-17 Mpa)
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Gap formed between adhesive and tooth
~ 5-20 microns
Managing Polymerization Shrinkage/Stress (5)
Incremental placement ◦ ¯ bonded/unbonded, each increment ◦ ¯ C-Factor, ¯ polymerization stress ◦ Is shrinkage reduced? ◦ No, stress is reduced
Self-cure composite
◦ Slower polymerization rate
◦ Internal flow, compensates for shrinkage
Soft-start cure - ¯ initial light intensity
◦ Decreased stress, disadv. - maybe ¯ conversion
Light-directed polymerization
◦ Composite does not shrink toward the light
Low shrinkage composite: Filtek LS 0.9% shrinkage ◦ Silorane resin, ring opening
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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
Universal adhesives
Chemistry game changer is
10-MDP Methacryloyoxy-decyl-dihydrogen-phosphate
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10-MDP Methacryloyoxy-decyl-dihydrogen-phosphate (4)
Mechanism of action : A monomer that chemically interacts via ionic bonding to calcium in hydroxyapatite
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
