Exam 1 review Flashcards
Characteristics of graph 1
Stiff
Ductile
Strong
Tough
Characteristics of graph 2
Stiff
Brittle
Strong
Characteristics of graph 3
Stiff
Ductile
Weak
Characteristics of graph 4
Stiff
Brittle
Weak
Characteristics of graph 5
Flexible
Ductile
Strong
Resilient
Characteristics of graph 6
Flexible
Brittle
Strong
Resilient
Characteristics of graph 7
Flexible
Ductile
Weak
Characteristics of graph 8
Flexible
Brittle
Weak
In the phase diagram there are ACB and ADB lines.
Above the ACB line is all ___.
Below the ADB line is all ___.
Between the lines is a mix of both - this area has a ____.
liquid
solid
melting range
Au and Cu are soluble in each other at any combination. When mixed together they form a ____.
solid solution
At certain concentrations of metals mixed together you may get an ____ solution. These solutions impart higher ____ and ____ to alloys.
ordered
hardness and strength
___ is used as a binder in materials commonly employed in the casting of dental gold alloys and is generally not heated above 700 C.
Gypsum
A binder is used to form a coherent ___ mass and to provide ___ for the investment.
solid
strength
___ is a binder used for gold.
___ are binders used for high temp alloys.
Calcium sulfate hemihydrate
Phosphate, Ethyl Silicate
A semicircular groove placed across one side of a block is considered a ___.
stress raiser
Stress is constant over most of the plane but would rise suddenly near the groove reaching a max at the edge of the groove.
Why can polymers absorb water?
Because of weak secondary bonds in polymers, water molecules are able to penetrate between polymer chains
___ alloys occur when 2 metals are soluble as liquids but nearly insoluble as solids.
Eutectic
The pure eutectic has a ____ that is lower than either of the pure components.
melting point (not a range)
What are the causes (environmental factors) of poor dimensional stability?
Syneresis
Imbibition
Evaporation
___ is fluid loss during setting squeezing water from between polysaccharide or alginate chains >> Shrinkage >> Distortion of cast
Syneresis
___ alginate powder is the most accurate way to dispense it.
Weighing
Where will a porcelain-metal bond most likely fail?
In the porcelain body
Why must the coefficient of thermal expansion (CTE) be compatible between porcelain and metal?
The materials will have a different contraction rate while cooling. The cooling metal should contract causing the brittle porcelain to become more densely packed and thus more sturdy.
What materials have the highest degree of thermal expansion?
Waxes
What is the composition of a High Noble metal?
- 60% Noble metal
- 40% Gold (Au)
What is the composition of a Noble metal?
- 25% Noble metal
- no specific gold stipulation
What is the composition of predominantly base metal?
- Noble metal less than 25%
What is the highest point of the stress/strain graph?
Ultimate Strength
In most dental alloys and ceramics, the U.S. and the Fs (fracture strength) will be very close
Which is higher on the stress/strain graph (and subsequently numerically), yield strength or proportional limit.
Yield strength is higher because materials begin to function in a plastic manner. (limited permanent strain HAS occurred)
Minute scratches on the surface of materials behave like sharp notches which are ________
Stress raisers
When stress suddenly rises near a “groove”, reaching a max at the edge of the groove is called _______?
This is a phenomenon that occurs around any irregularity in a material.
Stress raiser
What is higher a stress raiser or the average stress in the body?
The stress raiser. It can be several times higher. The amount of increased stress depend on the shape of the stress raiser.
Why do materials fail at stresses far below their expected strength?
Stress raisers allow stresses to reach the theoretical strength of the material at a relatively low stress. When the theoretical strength is exceeded at the tip of the notch the bonds break at the tip. The adjacent bonds are not the tip of the notch (and become the point of greatest stress concentration). Therefore, the crack will propagate through the material until the crack/fracture will move completely thorughtout the material.
What desired effect does Sodium Phosphate have when preparing an Alginate mixture?
Retarder. It’s a real thing.
What is syneresis?
Fluid loss during setting, squeezing water from between polysaccharide or alginate chains
What effect does syneresis have on a cast, and what should be done to avoid this effect?
Shrinkage –> Distortion
Pour impression ASAP! Do it now!
What is Imbibition?
What does it cause?
What should you avoid?
Uptake of water in the GEL state
Expansion
Don’t soak in water, rinse, or spray with disinfectant
How do you counteract the undesired effects of evaporation on alginate?
What will you get if you don’t address it?
Retard dimensional changes - wrap in wet paper towel and pour ASAP
Shrinkage. We all get it, but it can be avoided.
True or False: A high # of low MW molecules and a low # of high MW molecules may have the same average MW AND properties
FALSE
Same avg MW, but DIFFERENT properties
Some polymers, when heated, soften the material by breaking weak physical bonds, allowing the chains to slide past one another. When cooled, the bonds reform and the material hardens again. This property is called ___________.
Thermoplastic
Covently-bonded, cross linked polymers that do not soften on heating are termed:
Thermoset
Addition Polymerization:
Stage 1: ______ Stage
This stage creates _______, which attack double bonds of monomer molecules
Initiation
Free-Radicals
What role does sodium phosphate have in the composition of alginate?
retarder
What are the 3 environmental factors that give alginate poor dimensional stability?
syneresis, imbibition, evaporation
______ is fluid loss during setting, squeezing water from between polysaccharide or alginate chains. = shrinkage
syneresis
_____ is the uptake of water in gel
Imbibition
_____ is water loss due to environmental conditions
Evaporation
A ____ # of low mw molecules - a ____ # of high mw molecules, may have the same average mw but different properties
high, low
What is a thrermoplastic material?
When heated weak physical bonds break and the chains can slide past one another, result in a soft material. On cooling the bongs reform and the material hardens. Materials that under go this softening and hardening are thermoplastic.
What is the key feature of a thermoset polymer?
Cross inked polymers DO NOT soften on heating
What are the three stages of polymerization?
initiation, propagation, termination
What happens in the initiation stage of polymerization?
Free radicals are created which go and attack the double bonds of monomer molecules. Unshared electrons move to the end of the monomer thus activating the monomer molecules.
What happens in the propagation stage of polymerization?
Activated monomers attack double bonds of another monomer. More monomers are added to the free radical, and the chains grow in length.
What happens during the termination stage of polymerization?
Materials like hydroquinone, eugenol, or large amounts of oxygen inhibit polymerization by reacting with the free radicals. Decreases rate of initiation/ increases termination.
What is the setting reaction for Gypsum?
CaSO4 * 1/2 H2O + 1 1/2 H2O —> CaSO4 * 2H2O + Heat
What is the definition of setting rxns we don’t need to know just recognize?
Nucleated recrystallization, characterized by a continuous solution of hemihydrate, diffusion of calcium and sulfate ions to nucleation centers, and precipitation of microscopic gypsum crystals
Which phase is responsible for co-efficient expansion?
Leucite phase
What makes up the pigments added to porcelain?
Metallic oxides Titanium oxide = yellow-brown manganese oxide = brown iron oxide = brown cobalt oxide = bluecopper/chromium oxide = greennickel oxide = brown lanthanide oxides = fluorescence
What is the process of sintering?
Crown is dried at the door of the oven where it is heated under vacuum. Porcelain particles join together by flow on contact as a result of surface energy.
What will happen to ceramic metal bonds if oxide layer is too thick?
Fracture through the oxide layer. If that doesn’t make sense Ceramics slide 30
What are the two phases in porcelains?
Vitreous (glass) phase: properties of typical glass, brittleness, non-directional fracture pattern, translucency, high surface tension as a liquid.Crystalline (mineral/leucite) phase: high thermal expansion, content (10-20%) controls the CTE of the porcelain contributes strength.
Addition Polymerization:
Stage 2: ______ Stage
______ ______ ______ attack double bonds of other monomer molecules.
Chains grow in length
Propogation Stage
Activated Monomer Molecules
Addition Polymerization:
Stage 3: ______ Stage
Materials like hydropuinone, eugenol or oxygen will inhibit or retard polymerization by reacting with _______.
Termination
Free-Radicals
_________ the rate of polymerization: Decreases the degree of polymerization or molecular weight.
Decreasing
What reaction is this?
Gypsum Setting Reaction
What is this monstrous paragraph defining?
Nucleated recrystallization, characterized by a continuous solution of hemihydrate, diffusion of calcium and sulfate ions to nucleation centers, and precipitation of microscopic gympsum crystals. This is caused by DIFFERENCE IN SOLUBILITY of the two forms. Dihydrate is less soluble than hemihydrate.
Definition of the Gypsum Setting Reaction
Shattered mix of molten glass and leucite forms FRIT. After frit is formed, what pigmented materials can be added to produce various shades?
Metallic Oxides
_________ phase controls the CTE of the porcelain and contributes strength. It constitutes _____% of the overall content.
Crystalline (mineral/leucite)
10-20%
During sintering, the crown is heated under vacuum, and the ________ particles join together by ___ __ ____ as a result of surface energy
porcelain
flow on contact
2 phases of feldspathic dental porcelain:
Vitreous (glass) phase
Crystalline (mineral/leucite) phase
Which phase of feldspathic dental porcelain is responsible for high thermal co-efficient expansion?
Crystalline (mineral/leucite) phase
What process takes place when a crown is fired/heated under vacuum?
What is this first firing called?
Sintering
Biscuit Bake (It’s really the “Bisque” firing… I took ceramics in undergrad, so I can basically make pots with my bare hands. Like in “Ghost”. But cooler.)
In Ceramic-metal bonding, the _____ layer fractures the most, when it is too _____.
Oxide
Thick
In _____ bonding, the highest strength of ceramic-metal specimens fracture in the porcelain layer.
Proper bonding
What is the result of increasing the W/P ratio.
Decreased setting and thermal expansion
Decreased strength
Increased porosity
What is the result of decreasing the W/P ratio?
Denser cast
Hardens quicker
Thick mixes (___ W/P ratio) hardens more quickly because of ____ concentrated in smaller volume.
low
nucleation centers
What are the refractory and binding components of investor material? What do they do for the investor material?
Refractory - Silicon Dioxide (provides expansion to compensate for gold shrinkage)
Binding - Gypsum (provides strength)
What makes a material brittle?
inability to deform and redistribute stress. They cannot get atomic center materials to slide past one another.
How do you get a finer grain size in alloys?
- rapid cooling
- add very fine, high melting metal or oxide powder
___ is resistance to fracture
Toughness
___ is resistance to permanent deformation
Resilience
Which is more likely to fracture, long grains or fine grains? Why?
Large grains are more likely to fracture because they cannot slide well.
Fine grains have increased YS, Ductility, US, UTS and elongation.
___ occurs when 2 metals are soluble as liquids but nearly insoluble as solids.
Eutectic Alloys
____ is causing a plastic deformation by hammering, drawing, cold forging, cold rolling or bending. Produces many dislocations that can not slip easily through each other as the lattice becomes more distorted.
Cold working
