MDS PREP
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 is the mechanism of action for acid etching of dentin?
1) Formation of a smear layer.
2) Selective dissolution of hydroxyapatite crystals.
3) Dehydration of the dentin matrix.
4) Both A and B.
Acid etching selectively dissolves the hydroxyapatite crystals in dentin, creating microscopic tags and channels for resin infiltration, which enhances the bond between the restorative material and the tooth structure.
What is the effect of adding a nonionic surfactant to silicone impression materials?
1) Increases hydrophilicity
2) Decreases tear strength
3) Enhances setting time
4) Reduces dimensional accuracy
Adding a nonionic surfactant to silicone impression materials makes the surface more hydrophilic, allowing for better wetting of soft tissues and improved detail capture.
What is the minimum compressive strength required for lining materials?
1) 1.0 MPa
2) 3.0 MPa
3) 5.0 MPa
4) 10 MPa
Lining materials must have a minimum compressive strength of 5 MPa to withstand the forces in the oral cavity.
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 typical setting time for a high strength dental stone?
1) Less than 10 minutes.
2) 10-30 minutes.
3) 30-60 minutes.
4) More than 60 minutes.
High strength dental stones typically have a setting time of 30-60 minutes, which allows for sufficient working time while providing enhanced mechanical properties.
What is the primary function of the eugenol in zinc oxide-eugenol cement?
1) To provide antimicrobial properties
2) To act as a plasticizer
3) To initiate the setting reaction
4) To increase the compressive strength
The eugenol in zinc oxide-eugenol cement acts as a plasticizer, providing temporary softness for easier manipulation.
What are the three physical properties controlled by the ANSUADA Specification No. 1 (ISO 24234) for dental amalgam?
1) Creep, tensile strength, and thermal expansion.
2) Compressive strength, hardness, and density.
3) Creep, compressive strength, and dimensional change.
4) Tensile strength, modulus of elasticity, and corrosion resistance.
The specification controls the qualities of dental amalgam by listing requirements for creep, compressive strength, and dimensional change.