Week 4 Dental Materials Amalgam and Composite Flashcards
Alloy - metal
– a mixture containing two or more metallic elements or metallic and non metallic elements usually fused together or dissolving into each other when molten. Example: Brass is an alloy of zinc and copper.
T or F All metals (except iron and platinum) dissolve in mercury and mercury mixtures to create Amalgams
true
Dental amalgams consist of
mercury and a powdered alloy composed of silver, tin, and copper. Approximately 50% of dental amalgam is elemental mercury by weight.
Amalgam advantages
Ease of use
Direct material – placed in tooth in one appointment
High compressive strength
Excellent wear resistance
Favorable long-term clinical results
Economic
Can be bonded to tooth structure
Self-sealing ability
Least technique sensitive of all restorative materials
Applicable to a broad range of clinical situations
Disadvantages of amalgam
Poor Esthetic Qualities
Less conservative
Non-insulating
Corrosion at tooth restoration interface– may lead to “ditching” or marginal breakdown and eventual replacement
Galvanism
Concern about possible mercury toxicity
Difficulty in restoring proper tooth anatomy
Local allergic potential
Poor tensile and sheer strength
Silver in Amalgams
Causes setting expansion and increases strength and corrosion is resistant. Decreases creep and whitens the allo
Tin in Amalgams
Causes setting contraction and decreased strength. Reduces tarnish and corrosion
Copper in Amalgams
Copper – Increases hardness and strength and setting expansion.
Zinc in amalgams
If zinc is present and greater than 0.01% in amalgam, it is called zinc-containing amalgam. If the content is less, it is called non-zinc containing amalgam.
-Acts as a deoxidizer
-Zinc may increase the clinical life expectancy over amalgam that does not contain zinc.
Classification of dental amalgams based on copper content
-Low Copper alloy (2-6%)– traditional or historical composition. Approximately 65% silver; 25% tin, and less than 6% copper, with 1% zinc.
-High Copper alloy (10-30%)– clinical performance superior. Currently high-copper amalgams dominate the dental market.
(Increasing the copper content reduces the percentage of the weakest phase of the dental amalgam.)
Classification of dental amalgams based on zinc content
Zinc containing alloy - > 0.01%
Non-zinc containing alloy - < 0.01%
Classification of dental amalgams based on shape of alloy particle
Lathe cut alloy – sharp, pointy, irregular
Spherical alloy – round large and small
Admixed alloy – both together
Classification of dental amalgams based on size of alloy particle
micro cut, fine cute, coarse cut
Dimensional changes of amalgam is affected by
mercury/alloy ratio, trituration, and condensation techniques
T or F most modern amalgams exhibit very minor expansion or contraction on hardening if they are handled properly
true
Excessive contraction of amalgam can lead to
micro-leakage and secondary caries and sensitivity.
Excessive expansion of amalgam can lead to
sensitivity, pressure on the pulp, and protrusion of the restoration.
Excessive delayed expansion can occur if
a zinc-containing amalgam is contaminated by saliva or moisture during trituration or condensation. Starts 3-5 days after the restoration is placed and can continue for several months.
What forms the interface between the tooth and amalgam
corrosion, microleakage decreases over time around amalgams
Creep
Is a slow and progressive change in shape caused by compression.
-Low copper amalgam – 2.5% creep
-High copper amalgam – 0.2% creep
-Clinically creep leads to protrusion of restoration materials making the amalgam more prone to fracture and overhangs.
Does high or low copper amalgam have more creep potential?
low has more creep (2.5%) than high (0.2%)
T or F Amalgam is a good thermal conductor and should be protected with either varnish, liner or base
true
Mercury vapor is released during _________ of amalgam.
manipulation, placement and removal
Overview of placement of amalgam restorations
(A) prepared using undercuts to retain the amalgam
(B). The amalgam is mixed (triturated), then quickly placed into the preparations and carved into appropriate anatomic form
(C). After 24 hours or more, the amalgams may be polished to assure good contours, a smooth surface, and closed margins.
Dental Composite -
A synthetic resin, usually acrylic based, to which a high percentage of reinforcing filler has been added, such as particles of glass or silica coated with a coupling agent to bind them to the matrix; used in dentistry as restorative material or adhesives.
Dimethylglyoxime is also commonly added to achieve certain physical properties such as followability.
What is commonly added to achieve flowability to composites?
dimethylglyoxime
Applications of composite materials
Restoration for both anterior and posterior teeth
Pits and Fissure sealants
Bonding of ceramic veneers
Cementation of fixed prosthesis
3 big components of composite
1.Resin matrix (organic) polymer
2.Filler particles (inorganic), ceramic/fiberglass
3.Silane coupling agent
plus Initiators and accelerators that cause the material to set
Pigments – add color
Type of filler particles (inorganic) in resins
Silica Particles
Quartz or glass
Barium for radiopacity
Effect of filler particles in resins
Increase strength and wear resistance
Reduce shrinkage
Size and amount of filler particle in resins
Size varies
The higher the filler content, the stronger the restoration and the more wear resistant
Filled resin
made up of resin matrix and fillers
Resin matrix is made of
polymer: Bis-GMA (bisphenol-A + glycidyl methacrylate very viscous)
Low molecular weight monomer (TEGDMA: triethyleneglycol-dimethacrylate) added to reduce viscosity
Silane Coupling Agent
Silane – reacts with the surface of the inorganic filler and the organic matrix
siloxane end bonds to hydroxyl groups on filler methacrylate end polymerizes with resin
What do metal oxides do for a composite resin?
(inorganic) provide shading and opacity, titanium and aluminum oxides
Monomers
low molecular weight resin molecules
Polymers
long chain, high molecular weight molecules
Activators
– organic molecules composed of tertiary amines.
Activators + Initiator ->
Activators + Initiator -> Initiator Free Radicals
T or F Initiator Free Radicals break carbon double bonds on the monomers
true
Cross-linking of polymer chains
stronger, stiffer material
Composite Resin Polymerization: Chemical Cure
Two-paste systems
First paste (base) – composite + benzoyl peroxide as the initiator
Second paste (catalyst) – composite + tertiary amine as the activator
Mix equal parts of the two pastes to begin polymerization and cross-linking
Limited amount of working time after pastes are mixed
Composite Resin Polymerization: Light Cure
-Blue light cure light (400-500 nm) activates a diketone
-Camphorquinone is the most common photo initiator
-Initiator reacts with tertiary amine activator
-Depth of cure depends on the color and thickness of the resin
______is the most common photo initiator for light cure composite resin polymerization
Camphorquinone
How does a visible light cure work?
photo initiation reacts with tertiary amine activator
Composite resin classification by filler size
Macrofilled
Microfilled
Hybrid
Microhybrid
Nanohybrid
Nanocomposites
Flowable
Pit and Fissure Sealants
Core Buildup
Macrofilled resins
-Large fillers - crystalline quartz 10 to 100 microns
-Difficult to polish
-large particles prone to pluck from the surface due to wear.
-Relatively strong.
Examples: Adaptic, Concise
-No longer widely used
Microfilled resins
-Better esthetics and polishability
-Tiny filler particles, Average 0.04 micron colloidal silica.
-35 – 50% filled (rather low).
-Weaker, more shrinkage, and less wear resistant
To increase filler loading:
-filler added to resin
-heat cured
-ground to large particles (10 to 20 microns)
-remixed with more resin and filler
Hybrid filled resins
-Were popular as “universal” resins
-Both anterior and posterior use
-Filler particles – large and microfine filler particles for strength and polishability
-70 – 80% filled by weight
-Microfine – 0.04 to 0.2 microns
-Large – 2 to 4 microns
Good esthetics, polish smooth, strong, less polymerization shrinkage
Microhybrid filled resins
“all-purpose” or universal
-Filler particles – contain both small and microfine filler particles
-60 to 70% filled by volume
-Microhybrids contain a mixture of Small particles (0.04 – 1.0 microns)
Microfine particles (0.01 to 0.1 microns)
-Good esthetics, polish smooth, strong, less polymerization shrinkage (2 to 3%)
Nanohybrids: use nanosized particles (0.005 to 0.020 um)
Shrinkage reduced to about 1%
Nanocomposites
“all-purpose” or universal
Filler particles:75% filled by volume
Nanosized (individual spheroidal) particles added (5 to 75 nanometers)
Nanocluster aggregates (0.6 to 1.5 um)
Space between particles in the cluster filled with silane
Good esthetics, polish smooth, strong (low wear resistance), low polymerization shrinkage (about 1.4 – 1.6%)
Both anterior and posterior restorations
Flowable compsites
Low-viscosity, light-cured resins
Lightly filled (40%) up to 70%.
Particle size: 0.07 to 1.0 microns. Some are using nanohybrids.
Flow readily.
Conservative dentistry: preventive resin restorations (PRR).
Lower elastic modulus – more flexible – might be good in areas where the tooth will flex.
More resistant to wear than sealants.
Not good in high stress areas.
Pit and fissure sealants
low viscosity resins, vary from no filler to very little
Core Build up Composites
-Heavily filled
-Used to replace missing tooth structure before the tooth is prepared for a crown.
-Usually a different color than the tooth (blue).
-Chemical cure is popular due to the ability to place in larger increments and in deep areas of the preparation. -Light cure and dual cure is also available.
-Crown preparation can be completed at the same appointment.
Provisional Restorative Composite
Used in place of acrylic for provisional restorations.
More expensive than acrylic.
Easily repaired with flowable composite.
No heat when cured.
Can be brittle (multiunit bridges may fracture).
Examples: “Integrity”, “Luxatemp”.
Composition of glass ionomers
Polyacrylic acid + calcium aluminosilicate glass (contains fluoride)
Do glass ionomers need bonding agent?
no
Tooth prep for glass ionomer
Tooth is prepared with a weak acid (10% polyacrylic). Doesn’t remove calcium.
Powder and liquid combined – the acid attacks the glass, giving off calcium, aluminum, sodium, and fluoride
Calcium and aluminum cross-link the polyacrylic acid chains to form a hard resin matrix
Carboxyl groups from the acid combine with calcium on the tooth surface, creating a chemical bond between the tooth and the glass ionomer
Initial set is quick, takes 24 hours for final set
How long does glass ionomer take to fully set?
24 hours
Physical properties of glass ionomers
Biocompatibility: well tolerated
Bonds to calcium in the tooth structure
Fluoride release
Solubility: very sensitive to moisture during first 24 hours
Thermal expansion: similar to tooth
Thermal protection: good insulators
Mod high compressive and low tensile strength: no stress bearing areas
Wear resistance: wears faster than composites; hard to polish
Radiopacity: more radiopaque than dentin
Color
Clinical uses of glass ionomers
luting cements, restorative material (lamination sandwich technique) liners/bases, sealants
Hybrid Resin Modified Ionomers
-HEMA (hydroxyethyl methacrylate) resin added to glass ionomer to improve on it’s properties
Addition of resin increases strength, wear resistance, polishability, protect from moisture.
-Releases fluoride
-Light or chemically cured
-Used like glass ionomers
(no bonding agent needed)
Compomers
-The result of the composition of two different materials, composites and glass ionomer resulting in a compomer.
-Used to aesthetically restore anterior teeth where there is not a lot of occlusal forces (chewing).
-Resin: modified with polyacid
-Very little fluoride release
-Not much recharging of the fluoride
-Can be used where a microfilled composite would be used
Ionic Bond
electron given up by one atom and accepted by another.
Which bond is stronger, ionic or covalent
covalent
Covalent bond
two atoms share a pair of electrons
Type of bond in polymers
long chains of covalently bonded carbon atoms
Metallic bonds
similar to covalent, valence electrons are shared between atoms. Difference is that electrons in a metal object are not shared by two atoms–they are shared by all the atoms that make up that object. Positive cores surrounded by electron cloud
van der Waals forces
secondary bonds, result of partial charge from an uneven distribution of electrons around an atom or molecule. Secondary bonds are important in polymers because they determine the interaction of the polymer chains and the properties of the polymer itself.
Permanent dipoles
shared electrons not shared equally. Some atoms greedy. Creates one atom in the bond becoming partially positive and the other partially negative. Charged. ex. the interaction of partial charges reduces the slippage of carbon chains by one another in molecules of PVC, creates strong stiff plastic. When dipoles are smaller, material is weaker and less stiff (polyethylene plastic wrap)
Hydrogen bonds
special kind of STRONG permanent dipole. H contains only one electron. When pulled away to a greedy atom like Oxygen, it creates a much stronger bond because the H is left unshielded.
Fluctuating Dipole
intermittent, uneven distribution of electrons around the atoms or molecules. Lasts short time and is always changing, very weak attraction. Ex. Noble gasses have no charge distribution and no dipole so electrons move around willy nilly.
Secondary bonds
result of uneven electron distribution around atoms, the more uneven the distribution, the stronger the charge attraction and bond. Include permanent dipoles, hydrogen bonds, and fluctuating dipoles
Dental composites are a combination of
a ceramic and polymeric material
ductile
easily be bent without breaking yet retains strength
T or F Metallic bonds allow us to bend orthodontic wires and clasps in partial dentures or adapt gold restorations closely to the tooth while maintaining strength.
true
The atoms of ceramic materials are bonded with _____ bonds
ionic, strong when compressed but brittle/weak when pulled apart or bent
advantages of ceramic materials
esthetics: color and translucent to better match natural teeth.
Examples of polymers
Plastics–soft weak and flexible. (toys, garbage bags, fabrics)
Resins–hard stiff or strong AKA glassy polymers (plumbing, dishes)
Rubber– very stretchy and return to original shape (gloves, elastic)
The weakest bond between polymer chains is
fluctuating dipole
In dentistry, moldable polymers are used to make
bleaching and fluoride trays p.29
As the number and intensity of the charge increases in a permanent dipole, the strength and stiffnesss of the polymer _____
increases. Higher temperatures are also needed to melt these when processed.
Some polymers have cross link between the chains and are linked by covalently bonded atoms to form a 3D structure and can no longer slide past each other, resulting is _____ material
stiff, strong. Ex. collagen, wood fiber in plants. DENTAL COMPOSITE FILLING MATERIALS use cross-linked polymeric materials
Dental composite filling materials use _________ polymeric materials
cross-linked. Heat will not melt these polymers and chain cannot slip by each other. (if heated high enough they will break down and char, not melt)
One ionic bonded polymer used in dentistry
polyacrylic acid
The more cross links a rubber material has the _____ it will be
stiffer
Enamel is a composite of ____
apatite (ceramic material) and protein (a polymer)
Colloid
two phase material mixture of gas, liquid or solid. Not true solution (dissolved one into the other), SUSPENSION of one material in another.
Properties of colloid a result of
properties of the component materials BUT ALSO affected by the surfaces of the component phases. The large amount of surface area around the small particles gives them their properties. Ex. some dental impression materials, fluoride foams, jello, milk
Emulsions
type of colloid, two liquids that do not blend together to form one liquid even when vigorously mixed. ex. oil and vinegar dressing
Physical properties
laws of physics, mass, energy, force, heat, electricity, density, color etc
Mechanical Properties
sub group of physical, ability to resist forces. Depends on the amount of material and size/shape of the object (strength, stiffness)
Chemical Properties
setting reactions, decay of materials
Biologic properties
effects the materials have on living tissue
density
mass in a given volume, depends on the type of atoms present, packing together, and voids in material. High density will feel heavy
When an object melts or boils, the atomic bonds are ______ by the thermal energy of the material
broken
Vapor pressure
liquids tendency to evaporate to become gas
As the temp of a liquid increases, the vapor pressure _______
increases
______ vapor pressure materials are useful as solvents
High, as it evaporates it leaves behind the thinner layer of viscous liquid. (like varnish, dentinal adhesives. Perfumes, rubber cement, paint etc)
Thermal conductivity
a rate, measured as heat flow over time. Components: distance, area, and temperature difference between source and destination
Heat capacity
amount of thermal energy a material can hoard. Specific heat capacity is the amount of energy needed to raise the temp 1 unit of mass by 1 decree C.
Heat of fusion
amount of energy required to melt a material
Heat of vaporization
amount of energy needed to boil a material
Coefficient of thermal expansion
change in volume as temperature changes
A polymeric material (like polymathy methacrylate, early tooth colored restorative material) shrinks and expands ____ times more than tooth structures
7x
T or F Modern day filling material more closely match the coefficient of thermal expansion of teeth and their predecessors
true
The process of heating and cooling resulting in micro leakage, tooth sensivitiy, and recurrent decay is called ____
percolation
Polymers and ceramics are ______ conductors and called _____
poor conductors, called insulators
Viscosity
ability to flow, thick or thin liquid. Temperature dependant
T or F Wetting a surface with an adhesive material brings the material into intimate association with the surface so chemical and micro mechanical bonding can occur
true
______ contact angle creates good wetting
low, more spread out, short wide disc of liquid.
Durometers are use to measure _____
the hardness of impression materials and other elastic polymers
A restoration must be ______ enough s that the restoration does not wear away, but not so ____ as to excessively wear away the opposing teeth
hard
abrasive resistance
wear resistance
Water sorption
materials that absorb water. Many polymers absorb a small amount of water over time and slightly swell as a result.
strain
when load is applied to an object, stress develops that resists the load inside the object and will microscopically compress or elongate
stress
force that develops in a loaded object and is proportional to the applied force or load
The load (stress) and the change in length (strain) are ______
proportional. This proportion is called modulus of elasticity and measures stiffness
Enamel has a ____ modulus of elasticity. Rubber has a _____ modulus of elasticity
high (takes more to move, more stiff less flexible), low (doesn’t take as much to move, more flexible less stiff)
Compression
pushing or crushing stress
Tension
pulling stress
Shear
(slip) sliding by one another
Torsion
twisting stress
Bending
combo, one side is compressed and the other is stretched. shear forces also occur inside.
Poisson’s ratio
ratio of strain in the direction of the stress to the strain in a direction perpendicular to the stress. As you bite on a filling, it will compress smaller down and expand wider in the sideways MDFL dimensions.
Resilience
ability to absorb energy and not become deformed
Toughness
failure point on the stress-strain diagram
Fracture toughness
energy required to fracture a material when a crack is present
Which property is the best predictor of clinical success?
fracture toughnesss
Fatigue
failure after being stressed repeatedly over time
stress relaxation
slow decrease in force over time when material stretched to a constant state. the pull of a rubber band decreasing over time. Happens with ortho elastic and rubber bands so they need to change them often.
stress concentration
stress increases around defects and fracture becomes more likely.
yield strength
the point where the object will no longer return to original shape, stress and strain will no longer be proportional and graph will start curving
Because the mouth is a warm and environment, most materials will set ______ than on the countertop except for ones set by cooling or light activated materials
faster. If a material is set on a tray, it is set in the mouth already.
Some materials are accelerated by humidity of the mouth
true
Dispense equal _____ of pasts
lengths, not volumes
T or F after mixing alginate your arm should be tired
yes, mix aggressively
When mixing cements force the ____ into the _____
force the powder into the liquid
thermoplastic polymers
can be remelted and reprocessed after polymerization, similar to wax
thermoset polymers
cannot be heat and molded so they must be in the final shape when the polymerization reaction occurs. MOST DENTAL RESINS are cross linked thermoset polymers
Most dental resins are cross linked thermoset polymers
true
Acrylic resins
used as pink denture base, and anterior filling material but now obsolete due to recurrent decay susceptibility
Functional group
part of the molecule responsible for it’s chemical properties
Monomers
(functional group) molecules with a reactive group that participates in the polymerization reaction
Free radical polymerization or addition polymerization
chemical reaction of acrylic resins, an unpaired electron (free radical) is involved in the reaction. One monomer at a time is added to the polymer chain as the reaction proceeds.
Polymerization activation
initiator molecule can become activated by heat, light, or chemical reaction.
pg. 63
