MDS PREP
What is the typical depth of corrosion for most amalgam alloys?
1) 50 to 100 µm
2) 100 to 500 µm
3) 500 to 1000 µm
4) 1000 to 2000 µm
The average depth of corrosion for most amalgam alloys is 100 to 500 µm.
What is the primary function of a retarder in gypsum-based dental materials?
1) To accelerate the setting reaction.
2) To enhance the mechanical properties.
3) To prolong the working time.
4) To improve the dimensional stability.
Retarders in gypsum-based materials slow down the setting reaction by forming an adsorbed layer on hemihydrates, allowing more time for manipulation and placement before the material sets.
What is the typical concentration of camphorquinone used in dental composite resins?
1) 0.1 wt%.
2) 0.2 wt%.
3) 0.5 wt%.
4) 1.0 wt%.
Small quantities of camphorquinone, typically less than 0.2 wt%, are sufficient to initiate the polymerization process when the composite resin is exposed to blue light.
How does the elastic range of a wire affect its ability to be activated in orthodontic appliances?
1) A high elastic range allows for greater activation without causing permanent deformation.
2) A low elastic range allows for more precise and controlled activation.
3) The elastic range does not affect wire activation; it is only dependent on the force applied.
4) A wire with a high elastic range is more prone to permanent deformation during activation.
The elastic range of a wire determines the extent to which it can be deflected and still return to its original shape without permanent deformation. A wire with a high elastic range can be activated to a greater extent before it reaches its plastic range, making it suitable for larger tooth movements.
What is the typical setting time for gypsum-based products like dental plasters and stones?
1) Less than 10 minutes.
2) 10-30 minutes.
3) 30-60 minutes.
4) More than 60 minutes.
The setting time for gypsum products can range from a few minutes for impression plaster to up to 30 minutes for some dental stones, depending on the specific formulation and water to powder ratio.
What type of cement is most commonly used for cementing metal crowns and bridges?
1) Zinc oxide-eugenol
2) Zinc phosphate
3) Glass ionomer
4) Resin cement
Resin cements are commonly used for cementing metal crowns and bridges due to their high bond strength and durability.
Modern dental noble metal casting alloys generally have equiaxed fine grain structures because of the incorporation of small amounts of
1) Chromium
2) Indium
3) Iridium
4) Palladium
Dental Materials Answer: 3
The term equiaxed refers to the fact that three dimensions of each grain are similar. In dendritic structure, grains are elongated. Dendritic micro structures are not desirable for cast dental alloys, reason being the inter dendritic regions can serve as sites for
crack propagation.
Addition of about 1 wt% of ruthenium, Iridium or rhenium as grain refiners makes modern dental noble metal casting alloys as equiaxed microstructures.
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.