Material Science of Metal-Ceramics Flashcards
Ultimate strength, yield strength, modulus of elasticity, elongation, and hardness are ______ properties of dental materials.
Mechanical
The slope of a stress-strain curve indicates which mechanical property?
Modulus of elasticity
The end of the elastic stage, just before fracture, is indicative of which mechanical property?
Elongation
An increase in the modulus of elasticity (slope) will ______ stiffness.
Increase (stress is Y-axis, strain is X-axis)
What will occur when reaching the point of ultimate tensile strength?
Fracture
Density, LCTE, Electrical character, translucency, color, and wetting are _______ properties of dental materials.
Physical
Translucency and color are also known as ______ properties.
Optical
What does LCTE stand for?
Linear Coefficient of Thermal Expansion
Which has a higher UTS, enamel or dentin?
Dentin (UTS = ultimate tensile strength)
Which has a greater VHN, enamel or dentin?
Enamel (hardness)
Metals are strong and ________.
Ductile
Within the micro-structure of materials, slips occur at ________.
Dislocations
What is the axial reduction requirement for MCC preparations?
1.5 mm where esthetics are needed (0.3 mm metal+ 0.2mm opaque+ 1.0 mm porcelain)
Noble metals will resist _______, tarnish, and corrosion.
oxidation
Why are alloys used for cast metal and metal-ceramic restorations instead of pure metal?
Pure metals are too soft
What methods can be employed to improve alloy mechanical properties?
- Solid Solution Hardening
2. Grain Refining
For what purpose are noble metals strengthened through Solid Solution Hardening?
To resist deformation and to impede dislocations
What is solid solution hardening?
adding atoms of one element (the alloying element) to the crystalline lattice of another element (the base metal). The alloying element diffuses into the matrix, forming a solid solution.
How is “grain formation” used to strengthen noble metals?
Grain boundaries in metal will RESIST deformation. Therefore, making grains smaller and increasing the number of grain boundaries will lead to decreased deformation
What is the difference between grain “formation” and grain “refining” when strengthening noble metals?
Grain formation: increasing number of boundaries by forming grains from the molten metal
Grain Refining: decreasing grain size
Grain refining will have what benefits on noble metals?
Very fine grains = more boundaries (block dislocations), increased tensile strength, improved elongation, increased ductility and hardness
What are the three casting alloys present in noble metals?
Au, Pd, and Pt
How do casting alloys effect noble metals?
Increase hardness
Into how many categories are casting alloys classified?
four
What are the four classifications of casting alloys?
Type I: Soft (59-90)
Type II: Medium (90-120)
Type III: Hard (120-150)
Type IV: Extra Hard (>150)
Strength of alloys is determine by ______ Hardness Test.
Vicker’s
A casting alloy that is classified as having a “very high” noble metal content would have ____% gold.
> 80
A casting alloy that is classified as having a “high” noble metal content would have _____% gold.
> 40
True or False: A casting alloy that is classified as “noble metal” must be 25% gold.
False: 25% noble metal but NO GOLD REQUIREMENT
A casting alloy that is considered “predominantly base metal” would contain less than ____% noble metal.
25
The “Midas” product used in OSU Clinics is a material that is used for _____ NOT ______.
CVC (partial veneer crowns or onlays), not mcc
Midas is classified as Type____ based on Vickers Hardness, meaning its strength is 120-150.
Type III
True or False: Midas is a Noble Metal Alloy meaning that it contains 25% noble metal.
True. 25% noble metal without a gold requirement percentage
Which elements are present in Midas that act as a Solid Solution Hardener?
Gold and Pd
Which element is present in Midas to produce more refined grains?
0.01% Ir (always Ir or Ru)
Argenco Y+ is a Type III noble metal alloy that is _____ in color and is used for ________.
Yellow
Full Cast Crown and Bridge
Why do alloys have improved metal-ceramic bonding when compared to pure metals?
Alloys are oxidation resistant
What is “Super Star”?
It is a Type IV alloy (>150 hardness)
used for MCC
White appearance
Why is Super Star used for MCC but Midas cannot be used for MCC?
Super-Star contains tin with allows for Metal-Ceramic bonding
What is the grain refiner that is present in Super Star?
Ru
midas contains Ir
Which elements in Super Star produce solid solution hardening?
Au, Ag, and Pd
What is enamel’s Vicker’s Hardness rating?
~350 kg/mm^2
Dentin has a higher _____, whereas enamel has a higher ____ (mechanical properties).
UTS (tensile strength)
VHN (hardness)
Rank enamel, dentin, and metals from highest to lowest translucency.
Enamel (yes)
Dentin
Metal (not translucent)
What are the three components of Dental Porcelain?
70-80% Potash feldspar
10-30% Quartz….for the matrix
0-3% Kaolin (clay)….for the workability
What kind of bonds are associated with ceramics?
Ionic and Covalent
Rank ionic, metallic, and covalent bonds from highest to lowest strength.
(most) –Covalent, Ionic, Metallic– (least)
Which type of bond requires an equal sharing of electrons?
Covalent
What is the building block of Dental Porcelain?
SiO4 tetrahedron
Dental Porcelain contains noncrystalline silicate-glass and crystalline silicates ____ and _____.
Quartz (or crystobilite)
Leucite
True or False: Ceramics have bad optical properties because increased crystals decrease the translucency.
False: Ceramics have good optical properties EVEN THOUGH increased crystals will decrease translucency
Ceramics are stiff and _______; metals are stiff and ______; plastics are flexible and ______.
Ceramics: brittle
Metal: ductile
Plastic: ductile
Ceramics are weak in ______ forces.
Tension
Brittle fractures in ceramic is initiated from the ______ surface.
Internal
True or False: Fracture in dental ceramic will begin at the external surface due to cyclic fatigue.
False: Begins at INTERNAL due to cyclic fatigue and stress corrosion
_____ Flaws in ceramics are due to brittle fracture (atoms unable to deform) and low ____ strength.
Griffith’s
tensile
Ceramics have high ______ strength and act as a thermal/electrical ______.
Compressive
Insulator
What are the three requirements in order for porcelain to bond to metal?
- Porcelain must have a lower melting temp. than metal
- Porcelain must have a similar COTE to the metal
- Porcelain must wet the surface of the metal
The silica-glass of porcelain is modified with Na, K, Ca, and F in order to break up the matrix so as to ______.
LOWER the melting temperature
do not want the metal to melt in processing
If the metal shrinks/expands more than the ceramic during heating or cooling, _____ forces will be put on the ceramic. Is this bad?
Compressive
Its “okay” because ceramics have high CS
If the ceramic shrinks/expands more than the metal during heating or cooling, ______ forces will be put on the ceramic. Is this bad?
Tension
this is bad because porcelain has poor TS
“Wetting the Surface of Metal” refers to the creation of a _____ layer between the metal and glass by way of which element?
metal -oxide layer
silicon oxygen
Which element determines whether a material can be used for an MCC?
Sn (tin!…which is present in SuperStar and not Midas)
