MDS PREP
What are the advantages of using light-cured composites over chemically cured products?
1) Less porosity, less staining, increased strength, enhanced color stability, and control of working time.
2) Faster curing time, better translucency, and less shrinkage.
3) Longer shelf life and lower cost.
4) Higher wear resistance and easier to manipulate.
Light-cured composites do not require mixing, which reduces porosity and staining. They also allow for better control over working time and increased color stability due to the use of aliphatic amines.
What is the typical pH of a resin cement immediately after mixing?
1) Less than 2
2) Between 2 and 4
3) Between 4 and 7
4) Greater than 7
The pH of resin cements is usually slightly acidic after mixing, subject to variation in formulation.
VLC resins are also called
1) microwave-activated resins.
2) tertiary amine-activated resins.
3) light-activated resins.
4) heat-activated resins.
Dental Materials Answer: 3
The first light-activated systems were formulated for UV light to initiate free radicals. Today the UV light-cured composites have been replaced by visible blue-light-activated systems with greatly improved depth of cure, a controllable working time, and other advantages.
Because of these advantages, visibly light-activated composites are more widely used than are chemically acti wited materials.
What are the common types of water-based dental cements?
1) Zinc polycarboxylate
2) Calcium sulfate
3) Zinc oxide-eugenol
4) All of the above
Water-based cements include zinc polycarboxylate and calcium sulfate.
What is the primary mechanism of adhesion for resin cements?
1) Micromechanical retention
2) Chemical bonding
3) Physical adsorption
4) Ionic bonding
Resin cements primarily achieve adhesion through micromechanical retention and chemical bonding.
What is the purpose of using a voltage regulator with an amalgamator?
1) To maintain consistent speed regardless of line voltage.
2) To reduce the speed of the amalgamator.
3) To increase the speed of the amalgamator.
4) To monitor the temperature during mixing.
A voltage regulator helps maintain consistent speed and proper mixing of amalgam regardless of fluctuations in line voltage.
Polyethers are susceptible to dimensional change if immersed for a long time. The recommended maximum time to immerse in disinfectant is
1) 1 minute
2) 10 minutes
3) 30 minutes
4) 1 hour
Dental Materials Answer: 2
The polyethers are susceptible to dimensional change if immersed for a long time (>10 min) because of their pronounced hydrophilic nature.
Epoxy resins are compatible with which of the following impression material :
1) Polysulphide impression material
2) Polyether impression material
3) Agar
4) Alginate
Dental Materials Answer: 2
Epoxy resins
· Abrasion resistance is many times greater than gypsum
· More expensive
· Undergoes 0.1 – 0.2% shrinkage, thus their shrinkage is approximately equal to gypsum. This is less of problem with newer formulations & polyurethane resin.
· Their detail reproduction is better.
· Hydrocolloids, polysulfides are not compatible with them.