QUIZ 1 - GYPSUM Flashcards
What is the chemical name and formula of Gypsum?
Calcium Sulfate Dihydrate, CaSO4+2H2O
This is a study purpose cast which has a positive likeness of an oral cavity.
Model
This is a model that has a positive replica of an oral cavity.
Cast
This is a negative replica of an oral cavity.
Impression
This is used to make a positive replica of a PREPARED tooth.
Die Stone
A replica of a prepped tooth is made out of 4 materials, what are these?
Gypsum products, Epoxy resins, metal, refractive materials
This is the β (beta) form of calcium hemihydrate.
Dental Plaster
This is the α (alpha) form of calcium hemihydrate.
Dental Stone
What do you call the ratio in which water is mixed with the hemihydrate.
W/P Ratio (Water to Powder Ratio)
Time from addition of the powder to water until the mixing is complete.
Mixing Time
The duration between start of mix & point where material hardens.
Setting Time
Time from start to mix to the point where the consistency of the mix is no longer acceptable for usage of intended purpose.
Working Time (Dito na nagfufunction yung material.)
Impurities added to gypsum product (mixture) which reduces the setting time (bibilis)
Accelerators
Impurities added to gypsum products that enhance the setting time (pinapabagal tumigas)
Retarders
The process of heating gypsum for the manufacture of plaster
Calcination
In order for the dihydrate to become hemihydrate, it will go through the process of ______.
Calcination
Heating ground gypsum in an open kettle
Dry Calcination
Temperature of Dry Calcination
115°C
Product of Dry Calcination
Dental Plaster (β calcium hemihydrate)
Heating gypsum under pressure and in the presence of water vapor.
Wet Calcination
Temperature of Wet Calcination
125°C
Product of Wet Calcination
Dental stone (α calcium hemihydrate)
What is the process of boiling gypsum in 30% solution of Calcium Chloride called?
Dehydration by boiling chemicals
What is the product of Dehydration by boiling chemicals?
High Strength Dental Stone
Calcination:
CaSO4 + 2H2O —> _______
CaSO4 + 1/2H2O
What is the reaction of the plaster upon mixed with water?
It becomes exothermic (umiinit)
What do you call the time when there is a little reaction or a little to no rise in temperature?
Induction Period
Uses of Gypsum
General: For construction purposes
Orthopedic: For preparation of casts
Dentistry:
- Impression Plaster
- To mount the cast on the articulator
- For bite registration
- Dental investments
Types of Gypsum/Dental Stone Products
Type I - Impression Plaster
Type II - Dental Plaster
Type III - Dental Stone/Cast Stone
Type IV - Improved Dental Stone or Die Stone or High Strength Stone
Type V - Dental Stone, High Strength, High Expansion
Use of Type I Plaster
For making primary impression of edentulous oral cavity in complete denture fabrication.
Type I Plaster is composed of?
Plaster of Paris (colored and flavored)
Function of adding few modifiers to Type I Plaster
To regulate the setting time and expansion
Purpose of Type II Plaster
To produce study cast or primary casts.
To fill flasks during complete denture fabrication.
W/P ration of Type II Plaster
45:100
Shape of Type II Plaster
Irregular orthorhombic crystals
Purpose of Type III Dental Stone
It is used in making MASTER CAST.
Shape of Type III Dental Stone
Rods and prisms
W/P Ratio of Type III Dental Stone
30:100
Type IV Dental Stone is also known as ______?
Die Stone and High Strength Stone
Shape of Type IV Dental Stone
Cuboidal Crystals
W/P Ratio of Type IV Dental Stone
19-24:100
W/P Ratio of Type V Dental Stone
18-22:100
Two Types of Setting Expansion
Normal Setting Expansion
Hygroscopic Setting Expansion
Refers to the setting expansion when a gypsum product is allowed to expand in air (when placed on table or dry environment).
Normal Setting Expansion
Refers to the expansion of the gypsum products what it is allowed to set, immersed in water
Hygroscopic Setting Expansion
Tests for Setting of Gypsum Products
- Loss of Gloss Test
- Gilmore’s Test
- Vicat Needle Test for Setting Time
- Ready for Use Criterion
The strength of a stone is inversely proportional to the ______.
W/P Ratio
TRUE or FALSE: It is better to keep the amount of water as low as possible.
TRUE
What instrument must be used in measuring water.
Accurate Graduated Cylinder
What must be used for measuring the powder?
Note: SHOULD NOT BE MEASURED USING SCOOP
Proper Weighing Balance
Why must you not mix the plaster in full circle?
The plaster will incorporate bubbles which will make the cast brittle and prone to breakage.
If the mixing has to be done by hand, the bowl must be (1)____, (2)____, and (3)_____?
parabolic, smooth and abrasion resistant
Spatula should have a (1)____ and (2)____.
stiff blade and a convenient handle
What is the purpose of hot water?
It reduces mixing time
Example of Accelerators
Potassium Sulfate
Calcium Sulfate Dihydrate Crystals (From plasters that has already been set)
Salt (Not more than a pinch)
Rate of reaction is increased when
The temperature is increased to body temp
(Sa bibig unang magseset kaysa sa room temp because of our body temp)
Gypsum will not set when the temperature is
100°C
Example of Retarders
Borax
Blood
Saliva
Agar
Alginate
Cold Water
Why should we stir the water powder more vigorously during the mixing step?
To avoid air entrapments
