Dental Material MCQs - Gypsum Products

# Model plaster (white) used to cast study models before mixing with water, is largely composed of:
A. CaO
B. CaCO3
C. (CaSO4)2. 1/2H2O
D. CaSO4.2H2O

# The product, which is obtained by calcining under steam pressure at 120-130°C or by dehydrating gypsum in the presence of sodium succinate is:
A. Alpha - hemihydrates
B. Beta - hemihydrates
C. Calcium sulphate dihydrate
D. Orthorhombic anhydrate

# Water powder ratio of dental stone and plaster is respectively:
A. 0.28 and 0.6
B. 0.6 and 0. 28
C. 0.6 and 3.2
D. 0.28 and 0.98

# Type III Dental gypsum is:
A. Class II stone
B. Densite
C. Class I stone or hydrocal
D. Model or lab plaster

# Green strength with reference to plaster means:
A. Dry strength
B. Compressive strength
C. Strength of dental stone due to green colour
D. The wet strength

# Beta hemihydrate particles absorb:
A. more water
B. less water
C. no water
D. none of the above

# Water of reaction needed to react completely with 100 g of calcium sulphate hemihydrates to convert it to calcium sulphate dihydrate:
A. 18.6ml
B. 22.2ml
C. 30.4ml
D. 45.3ml

# Powders of dental plaster and dental stone differ mainly in:
A. Solubility
B. Shelf life
C. Chemical formula
D. Particle porosity

# Plaster of paris is mixed in:
A. Plastic bowl
B. Rubber bowl
C. Glass bowl
D. Metal bowl

# Impression plaster containing potato starch is called:
A. Plaster of paris
B. Soluble plaster
C. Anti - expansion solution
D. Die stones

# Die is:
A. Impression of single tooth
B. Impression of whole teeth
C. Replica of single tooth
D. Replica of whole teeth

# Balanced stone is dental stone:
A. Which undergoes rapid expansion
B. In which accelerators or retarders have been added according to need
C. In which amount of water of hydration is controlled
D. In which the crystals are all of uniform size

# The main ingredient in dental plaster is:
A. Calcium sulphate hemihydrate
B. Calcium phosphate
C. Calcium anhydrate
D. Calcium sulphate dihydrate

# The strength of the gypsum specimen when the water in excess of that required for the hydrate of the hemihydrate is left in the specimen is called?
A. Dry strength
B. Green strength
C. Water strength
D. Compressive strength

# Accelerators and retarders are used with gypsum products mainly to control:
A. Setting time
B. Setting expansion
C. Hardness of the set product
D. None of the above

# Gypsum is used for?
A. Impressions
B. Casts
C. Die
D. Casts and Dies

# The hygroscopic technique is associated with:
A. Investment
B. Hydrocolloids
C. Amalgam
D. Silicate

# The main difference between dental stone and dental plaster is:
A. Chemical composition
B. Shelf life
C. Shape and size of particles
D. Solubility in water

# The most commonly used accelerator in gypsum product is:
A. Sodium fluoride
B. Potassium fluoride
C. Potassium sulfate
D. Aluminium sulfate

# As per ADA No. 25, minimum amount of setting expansion required for type V gypsum product is:
A. 0.05
B. 0.10
C. 0.15
D. 0.20

# Which is a gypsum product?
A. Stone
B. Plaster
C. Investment
D. All of the above

# Plaster of paris:
A. Is wet calcined hemihydrate
B. Has porous and irregular crystals
C. Is alpha hemihydrate
D. Has a W / P of 0.2

# In plaster of paris the setting time is primarily altered by:
A. Altering P / L Ratio
B. Altering temperature of mixing water
C. Speed and length of hand spatulation
D. Addition of accelerators and retarders

# Type I gypsum product is also called:
A. Impression plaster
B. Class I stone/ Hydrocal
C. Class II stone/Densite
D. Model plaster

# The beta hemihydrate of gypsum requires more water to float its powder particles because:
A. They are more regular in shape and dense
B. They are more regular in shape and highly porous
C. They are more irregular in shape and porous
D. They are more dense and prismatic in shape

# Setting of Plaster of Paris is result of:
A. Difference in solubility of CaSO4 1/2 H2O + CaSO4•2H2O
B. Reaction between CaS04 2H2O and water
C. Nucleation and growth of CaSO4.1/2 H2O crystals
D. Reaction between hemihydrate and dihydrate

# Placing cast under tap water is to be avoided as:
A. H2O interferes with hygroscopic expansion
B. H2O In hibits polymerization of dental resin
C. H2O interferes with crystallization of dihydrate
D. Gypsum is slightly soluble in water and the surface of the cast will be eroded

# Gillmore needle is used for:
A. Testing the strength of plaster of paris
B. Evaluating the setting time of plaster of paris
C. Testing the metal hardness
D. Testing the purity of noble metals

# 2 % solution of borax is used as a surface hardening agent for:
A. Casting stone
B. Dental plaster
C. Dental stone
D. Type IV gypsum

# Gypsum product having least expansion:
A. Impression plaster
B. Model plaster
C. Stone plaster
D. Die stone

# Modifiers are added to gypsum mainly to:
A. Modify setting time
B. Modify setting expansion
C. Modify strength
D. Decrease the porosity

# Most commonly used retarder in gypsum:
A. Na2SO4
B. NaCl
C. Citrates
D. K2SO4

# ADA specification number for gypsum products are described under:
A. 1
B. 4
C. 12
D. 25

# The setting expansion of gypsum products can be reduced by:
A. Increased spatulation
B. Adding potassium sulfate
C. Less water powder ratio
D. Allowing setting under water

# Finer particle size of silica:
A. Slower the hygroscopic expansion
B. Greater the hygroscopic expansion
C. Normal setting expansion
D. No setting expansion

# A rough/ chalky surface of the cast is due to:
A. Not waiting for 20 min before pouring
B. Excess wetting agent left on impression
C. Air incorporation in the mix
D. All of the above

# The function of 2% potassium sulphate in a gypsum product is:
A. To regulate the setting expansion
B. Regulate setting time
C. Acts as retarder
D. None

# Plaster mix:
A. Rapid spatulation results in decreased setting time
B. 2% potassium sulphate is accelerator
C. Citrates are retarders
D. All of the above

# The strength of gypsum products is generally expressed in terms of:
A. Tensile strength
B. Wet strength
C. Green strength
D. Compressive strength

# Water: powder ratio for class IV stone is:
A. 0.22-0.24
B. 0.24-0.28
C. 0.65-0. 70
D. 0.45-0.50

# Within practical Limits, using Less water in mixing plaster will result in a set product that:
A. Contracts
B. Is stronger
C. Is more porous
D. Is less brittle

# Increased spatulation is case of dental stone results in:
A. Increased working time
B. Increased setting time
C. Decreased setting time
D. None of the above

# In dental materials setting time is measured by which test?
A. Rockwell test
B. Cold blend test
C. Vickers test
D. Vicat needle method

# Which of the following is false regarding setting of plaster products?
A. Setting expansion increases with increase in nucleic density
B. Most accurate method of controlling setting expansion is by chair side addition of chemicals
C. Potassium sulphate is an accelerator and reduces the setting expansion
D. Maximum acceleration effect for sodium sulphate is approximately 3.4%

# Which of the following is incorrect about non-gypsum die material?
A. All impression materials are compatible with these
B. Polyester produces the most accurate dies
C. Epoxy resin dies are undersized but are used due to their higher abrasion resistance
D. Metal dies are preferable to high strength gypsum dies for captek restoration

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