Which gypsum product has the highest surface hardness?

(a)  

• Type II
• Type III
• Type IV
• Type V

What is the main purpose of adding potato starch to impression plaster?

• Better dimensional stability

• Easy separation of cast from the impression

• More accurate impression

• Prolong the working time

The α & β hemihydrates differ mainly in terms of thei

(a)  

• Chemical composition
• Particle shape & size
• Shelf life
• Solubility in water

Setting of die stone is the result of

• Difference in the solubility of CaSo₄ . ½ H O & CaSO4.2H O

• Nucleation & growth of CaSo₄ . ½ H₂O crystals

• Precipitation of CaSo₄ . ½ H₂O crystals

• Reaction between CaSO₄ .2H₂O and water

The strength of gypsum products is generally expressed in terms of

(a)  

• Compressive strength
• Flexural strength
• Green strength
• Tensile strength

Dental plaster

(a)  

• Has porous and irregular crystals
• Has water: powder ratio of 0.22
• Is wet calcined hemihydrate
• Is α-hemihydrate

The main reason why higher water: powder ratio should be avoided during manipulation of die stone is, because it

(a)  

• Decreases setting expansion
• Decreases strength
• Decreases working time
• Increases setting time

An increase in the no. of nuclei of crystallization will result in

• Higher strength

• Higher setting time

• Lower setting expansion

• Lower surface hardness

Gillmore needles are used to measure

• Setting expansion

• Setting time

• Strength

• Surface hardness

What is the setting time of dental stone in minutes?

• 4±1

• 8±2

• 12±4

• 16±6