MDS PREP
What is the main disadvantage of using zinc phosphate cement?
1) Low compressive strength
2) Potential for pulpal irritation
3) Difficulty in removal
4) High cost
While it has good mechanical properties, poorly placed zinc phosphate cement can cause pulpal irritation.
What is the primary use of sodium chloride as an accelerator in gypsum-based materials?
1) To increase the setting temperature.
2) To accelerate the setting reaction.
3) To improve the mechanical properties.
4) To prolong the working time.
Sodium chloride acts as an accelerator in gypsum-based materials by increasing the solubility of the hemihydrate, thereby speeding up the conversion to dihydrate and the overall setting process.
How is platinized gold foil formed?
1) By mixing gold and platinum powders and then beating them
2) By rolling gold and platinum sheets together to form a laminated foil
3) By plating gold onto a platinum substrate
4) By fusing a platinum rod with a gold ingot
Platinized gold foil is a combination of gold and platinum where 15% of the content is platinum. It is produced by rolling layers of gold and platinum together to achieve the desired thickness and distribution of the platinum within the gold foil. This process creates a homogeneous mixture that enhances the hardness and wear resistance of the restoration, making it suitable for high-stress areas like incisal edges and cusp tips.
What is the primary advantage of zinc polycarboxylate cement?
1) High thermal conductivity
2) Low film thickness requirement
3) Chemical bonding with tooth structure
4) Fast setting time
Zinc polycarboxylate cement was formulated to have the strength of zinc phosphate and the biological acceptability of zinc oxide-eugenol cements, with the added advantage of chemical bonding to tooth structure.
What are the main properties of Compomers?
1) High elasticity and high load deflection rate.
2) High modulus of elasticity and low shrinkage.
3) Easy to inject, shape, and polish with good aesthetics.
4) High thermal conductivity and good radiopacity.
Compomers are known for their ease of use, being non-sticky, and simple to place and shape. They are a hybrid of glass ionomer and composite resin properties, offering good aesthetics and user-friendly handling.
What is the structural formula of the substance found in irreversible hydrocolloid?
1) Anhydro-?-d-mannuronic acid
2) Anhydro-?-d-glucuronic acid
3) Anhydro-?-d-glucuronic acid
4) Anhydro-?-d-mannuronic acid
Irreversible hydrocolloid, such as alginate, is based on the structure of anhydro-?-d-mannuronic acid.
What is the by-product of the condensation setting reaction in silicone elastomers?
1) Water
2) Ethyl alcohol
3) Carbon dioxide
4) Oxygen
The condensation reaction in silicone elastomers produces ethyl alcohol, which evaporates during setting, contributing to the material's contraction.
Which type of amalgam alloy has the lowest compressive strength at 1 hour?
1) High-copper lathe-cut alloy
2) Low-copper lathe-cut alloy
3) High-copper spherical alloy
4) Low-copper spherical alloy
The compressive strength at 1 hour is lowest for the low-copper lathe-cut alloy, which is 45 MPa.