Ch 47 Flashcards
Speciality Practices?
orthodontics, pediatric, and prosthodontics
biohazards
items bought into the lab the can harbor infective blood and saliva
infective blood and saliva are?
biohazards
MSDS
material safety data sheet
study cast/models/diagnostic cast
3d reproductions of the teeth and soft tissue of patients max and many. arches
a mineral mined from earth
gypsum
dihydrate
gypsum in its unrefined state
gypsum in powdered state
hemihydrate
What does the dihydrate form of calcium sulfate mean?
It means that it consists of two parts water to every one part calcium sulfate
What does the hemihydrate form of calcium sulfate mean?
It means only one-half part water to one part calcium sulfate.
materials used to make dental models
gypsum
types of gypsum
model plaster
____________
highstrength stone
types of gypsum
highstrength stone
dental stone
_________
When you mix gypsum powder with water….
the hemihydrate crystals dissolve in water to form clusters known as the nuclei of crystallization
Nuclei of crystallization
hemihydrate crystals dissolved in water
What occurs with more intermeshing of the gypsum crystals
The more meshing that occurs, the greater the strength, rigidity, and hardness of the final product
As the gypsum crystals grow during the setting process
they intermesh and become entangled with each other
all 3 forms of gypsum consist of….
hemihydrate crystals
Which form of gypsum has the densest crystals?
High-strength stone
Which form of gypsum requires the most water for mixing
Model plaster
differences of gypsums
size, shape, porosity of hemihydrate crystals
dental plaster aka
plaster of paris
dental plaster
white in color
what is used to pouring impressions to make diagnostic models
dental plaster
the crystals in ___ are irregular in shape and porous
plaster
Model plaster requires the greatest quantity of water for mixing
which produces the weakest of the three forms of study model
yellow in color
stone
stone is used for a ….
more durable diagnostic cast is required
dental stone crystals are…..
uniform in shape and less porous
stone is …..
strong and denser
Although stone is uniform and less porous it is….
less uniform in shape and more porous than those found in high-strength stone.
High strength stone aka
densite or improved dental stone
High strength stone has…….
the strength, hardness, and dimensional accuracy that make it ideal for use by the dental laboratory technician
crystals in high strength stone are…
smooth, dense, and require less water for mixing
which gypsum is used mostly for dental lab techs?
high strength stone
which gypsum is ideal for dental lab techs bc of its strength, hardness, and dimensional accuracy?
high strength stone
die is used for….
making wax patterns for crowns, bridges, and indirect restorations
plaster powder/water ratio
100 g) to 45 to 50 mL of water
dental stone p/w ratio
100 g) to 30 to 32 mL of water
high strength stone p/w ratio
(100 g) to 19 to 24 mL of water
when too little water is used….
it will be difficult to mix and shorter working time
too much water…
mix will be thing and runny and longer setting time. the model will be weaker
add all powder to water at same time or…
the crystallization process will be disturbed and the model will be weak
