fixed Flashcards
Does impression material get larger or shrink upon setting
shrink
Rigid impression materials:
zinc oxide and eugenol impression paste
impression plaster
For synthetic elastomers, ____ polymerize into elastomers?
oligomers
LIGHT body has ___ viscosity and ____ setting contraction
low viscosity
high setting contraction
Thermoplastic polymer:
Thermoset:
thermoplastic: no-cross linking. physical state reversible by temp (wax)
thermoset: has cross-linking
Condensation polymerization results in a:
by-product
POLYSULFIDE needs a _____ of impression material to stay accurate
minimum amount
Silicones (Polysiloxanes) are inherently ____ but the addition type can be made more ______
hydrophobic
hydrophilic
Addition silicone (polyvinylsiloxane) you should wait to pour model until:
hydrogen liberated
Most hydrophilic impression material?
polyether
Good wetting = ____ contact angle
low
Die stone has __% expansion.
Gold alloy can shrink up to __%
0.1%
Gold=2%
Starting material for gypsum is calcium sulfate __hydrate
di-hydrate
Typical water-to-powder ratio of high-strength die stone:
0.2-0.3
Common accelerator:
Common retarder:
What can be used for both:
accelerator: potassium sulfate
retarder: borax
both: NaCl
Which die stone type has lowest setting expansion and contain larger amounts of modifiers?
Which die stone is high strength AND high expansion (for “modern” use)?
Type IV
Type V
Gypsum has very _____ compressive strength, but very ___tensile strength
high compressive
low tensile
Composition of gypsum-bonded casting investment powder:
refractory (quartz): 1/2 - 2/3
binder (stone): 30-45%
chemical modifiers: 3% or less
Gypsum is _____ form in set material
dihydrate
Cristobalite, quartz, and tridymite are versions of ____.
Which has highest thermal expansion?
SiO2
Critobalite
Normal thermal expansion with temp increase..
Cristobalite:
Quartz:
Cristobalite: 200-270C
Quartz: 575C
What is special solution?
Silica sol in water
Advantage of phosphate-bonded investment:
withstand burnout temp of 900*C
Effect of length of deflection:
Effect of connector height on deflection:
D=L^3
D=1/(H^2)
Crown/root ratio
2:3
Modified hygienic pontic just has ____ connectors than normal
wider
What is an ovale pontic
goes into gum space
Retention form:
Resistance form:
retention: POW
resist: lateral
1 cause of FPD failure:
caries (23%)
Glass will adhere to _______ metal if covered with _____ and temp raised where _____ is partially dissolved into the metal
clean, gas free
adherent oxide
You want 90* metal/porcelain junction (T/F)
True
Zinc _____ cement has moderate pulp irritation. Adequate strength. Use cool glass slab.
Zinc _____ is only used for single metal units with less stress.
phosphate
polycarboxylate
Why is glass ionomer cement hard to use?
any moisture ruins it.
Which cement has highest compressive strength?
Which cements release flouride
glass ionomer
glass ionomers
which cement is highest strength?
composite resin
Pretzel has high ___ and low ___.
Twizzler has high ____ ability
high strength, low strain
strain
What has higher tensile strength (dentin or enamel)
dentin
Mechanisms to improve alloy mechanical properties:
solid solution hardening + grain refining
Small amounts of _____ produce metals with very fine grains
Ir + Ru
Casting alloy hardness classification..
Type I is ____ while Type IV is _____
I = softest IV= hardest
3 components of dental porcelain
potash feldspar
quartz
kaolin (clay)
what kinds of bonds does ceramic have?
ionic and covalent
Building block of dental porcelain:
SiO4
Melting point of porcelain must be ____ than metal
LOWER
Porcelain must ____ the surface of metal
wet
