Working time of gypsum products can be increased by

• Using slurry water for mixing

• Faster spatulation

• Increasing the water: powder ratio

• Increasing the time of mixing within practical limits

The length & Diameter of Vicat penetrometer are

(a)  

• 1cm, 1 mm
• 5cm, 1mm
• 1cm, 5mm
• 5cm, 5 mm

Accelerators and retarders are used with gypsum products mainly to control

(a)  

• Mixing time
• Setting time
• Setting expansion
• Strength of the set product

Which is the most commonly used accelerator in gypsum product?

(a)  

• Aluminum sulfate
• Potassium fluoride
• Potassium sulfate
• Sodium fluoride

A gypsum cast can be safely removed from the impression at the end of

(a)  

• Final setting time
• Initial setting time
• Mixing time
• Working time

A retarder can slow down the setting reaction of dental stone by the following mechanism:

• Enhancing the solubility of hemihydrate

• Increasing the precipitation of dihydrate

• Inhibiting the crystal growth

• Providing greater number of nuclei of crystallization

The main purpose of adding modifiers to gypsum products is to modify their

(a)  

• Rate of reaction
• Setting expansion
• Strength
• Surface hardness

Using higher water: powder ratio while mixing Type II gypsum product will increase it’s

(a)  

• Setting expansion
• Setting time
• Strength
• Surface hardness

Shorter setting time of impression plaster compared to dental stone is mainly due to

• Difference in their chemical composition

• Difference in their mixing time

• Higher water:powder used for mixing dental stone

• Presence of chemical modifiers in impression plaster

Mixing dental plaster in unclean bowl which contains fine gypsum particle residues should be avoided mainly because it

• Affects the color of plaster

• Decreases the time available for manipulation

• Lowers the setting expansion

• Lowers the strength of dental plaster