MDS PREP
What is the primary cause of delayed expansion in zinc-containing low-copper or high-copper amalgams?
1) Contamination by oxygen during trituration.
2) Contamination by water during trituration or condensation.
3) Over-trituration.
4) The presence of the ?2 phase.
A large expansion can take place if the amalgam is contaminated by moisture during trituration or condensation, known as delayed expansion or secondary expansion.
What is the typical composition of Zinc Oxide-Eugenol Cement?
1) Zinc oxide and polyacrylic acid
2) Zinc oxide and eugenol
3) Zinc phosphate and polyacrylic acid
4) Zinc oxide and sodium silicate
Zinc Oxide-Eugenol Cement is primarily composed of zinc oxide and eugenol, with a pH of approximately 7, making it less irritating to pulpal tissues.
What is the liquefaction temperature of agar hydrocolloid?
1) 37°C - 50°C
2) 60°C - 70°C
3) 70°C - 100°C
4) 50°C - 65°C
Agar hydrocolloid must be heated to a liquefaction temperature between 70°C and 100°C to be suitable for impression taking.
What is the water sorption value of poly (methyl methacrylate) according to the provided information?
1) 0.69 mg/cm²
2) 0.85 mg/cm²
3) 1.05 mg/cm²
4) There is no information provided on water sorption value
The text states that poly (methyl methacrylate) has a water sorption value of 0.69 mg/cm², which affects its dimensional stability and physical properties.
What is the elastic limit of a wire, and what happens when a wire is deflected beyond this point?
1) The elastic limit is the point at which the wire begins to deform plastically.
2) The elastic limit is the force needed to permanently deform a wire.
3) The elastic limit is the maximum force a wire can withstand before fracture.
4) The elastic limit is the point at which a wire will always return to its original shape regardless of the force applied.
The elastic limit, also known as the yield strength, is the point at which a wire starts to undergo permanent deformation. When a wire is deflected beyond this point, it does not return to its original shape completely.
Nitinol has the disadvantage of which of the following?
1) It cannot be formed into desired shapes
2) It lacks elastic properties
3) Its strength is not suited for orthodontic purposes
4) It lacks stiffness
Dental Materials Answer: 1
Nitinol is a metal alloy – or mixture – of nickel and titanium. This type of wire is also known as “memory wire” or “smart wire,” and it can be used for braces.
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.
What is the maximum allowable dimensional change for amalgams according to ANSI/ADA Specification No. 1?
1) Not more than 10 µm/cm.
2) Not more than 20 µm/cm.
3) Not more than 30 µm/cm.
4) Not more than 40 µm/cm.
The specification requires that amalgam neither contract nor expand more than 20 µm/cm.