MDS PREP
What is the weakest phase in amalgam and what happens if it is not eliminated or present in sufficient amounts?
1) The y phase is the weakest and is the most susceptible to corrosion.
2) The x phase is the weakest and is the most susceptible to corrosion.
3) The ? phase is the weakest and is the most susceptible to corrosion.
4) The ? phase is the weakest and is the most susceptible to corrosion.
The presence of the y phase makes the amalgam more susceptible to corrosion, and high-copper amalgams are designed to eliminate or significantly reduce this phase.
What is the function of benzoyl peroxide in the composition of denture base resin powder?
1) It acts as a filler
2) It acts as a cross-linking agent
3) It acts as an initiator
4) It acts as an inhibitor
Benzoyl peroxide in the powder of denture base resin is responsible for initiating the polymerization process when it reacts with the monomer in the liquid component.
What is the typical setting expansion of a regular dental stone?
1) Less than 0.1%.
2) 0.1-0.2%.
3) 0.2-0.3%.
4) More than 0.3%.
Regular dental stones have a low expansion rate, usually between 0.1% and 0.2%, which is suitable for accurate model fabrication.
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.
Before restoring a tooth with composite, the area is etched. Accidental contamination occurs with saliva, Therefore
1) the area is re-etched before restoration
2) the area is air-dried using an air spray and continue with restoring
3) wipe the saliva with cotton and continue to restore.
4) add excess composie material and cure it
Dental Materials Answer: 1
Etching of tooth surface with 37% phosphoric acid creates microporosities in the enamel and dentin. This is the main method of adhesion of composite resin to tooth surface.
After etching the surface energy of the enamel will increase. This will make it very sticky to any kind of contaminants. If salivary contamination will occur, the salivary proteins will precipitate in the microporosities. This will prevent the adequate penetration of the bonding agent, therby reducing the micotag formation. Hence, complete isolation is essential.
What is the primary purpose of using a thermal insulating base?
1) To protect the pulp from thermal changes
2) To increase the strength of the restoration
3) To improve the aesthetics of the restoration
4) To facilitate the removal of the restoration
The purpose of a thermal insulating base is to protect the pulp from temperature changes during the placement of a restoration.
What is the general source of the substance used in irreversible hydrocolloid impression material?
1) Synthetic polymer
2) Plant resin
3) Brown seaweed
4) Petroleum by-product
The material is derived from the structural formula of anhydro-?-d-mannuronic acid, which is extracted from certain types of brown seaweed.
What is the ideal thickness of a luting agent film for it to be effective?
1) 50 µm
2) 25 µm
3) 10 µm
4) 5 µm
An effective luting agent must be able to flow into a continuous film of 25 µm thickness or less without fragmentation.