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.
Ability of an orthodontic wire to spring back to Its original shape is evaluated by
1) Brittleness
2) Resilience
3) Tensile strength
4) Toughness
Dental Materials Answer: 2
Resilience is the amount of energy absorbed by a structure when it is stressed to proportional Limit.
The elastic area of the stress-strain graph gives resilience; entire area up to breaking point is a measure of toughness.
The slope of straight Line gives Young’s modulus.
What is the typical film thickness for a resin cement?
1) 50 µm
2) 25 µm
3) 15 µm
4) 5 µm
Resin cements are generally applied in a film thickness of 25 µm or less for optimal performance.
What is the primary mechanism of bonding for resin-modified glass ionomer cements?
1) Micromechanical retention
2) Chemical bonding to tooth structure
3) Ionic bonding
4) Physical adsorption
Resin-modified glass ionomer cements bond through micromechanical retention and chemical bonding.
What is the minimum 24-hour compressive strength required for dental cement according to ANSI/ADA Specification No. 96 (ISO 9917)?
1) 50 MPa
2) 70 MPa
3) 100 MPa
4) 150 MPa
The text states that the standard luting consistency of dental cement must exhibit a minimum 24-hour compressive strength of 70 MPa.
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 Today the UV light-cured composites have been replaced by visible blue-light-activated systems with greatly improved depth of cure, a controllable working time, and other advantages.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.
Which of the following denture base materials has the highest linear shrinkage?
1) High-impact acrylic resin
2) Vinyl acrylic resin
3) Conventional acrylic resin
4) Rapid heat-cured acrylic resin
Rapid heat-cured acrylic resin has the highest linear shrinkage at 0.97%, which can affect the fit and stability of the denture.
Porcelain binds to metal in PFM crown by:
1) Metallic bind
2) Mechanical bond
3) Chemical bond
4) Both 2 and 3
Dental Materials Answer: 4
Porcelain binds to metal in metal ceramic restorations by mechanical interlocking and chemical bonding. Mechanical interlocking is provided by proper wetting of the metal surface by porcelain.
The adherent metallic oxides, which are formed during the degassing cycle form a good chemical bond with porcelain.
Tin oxide and Indium oxide are formed from precious metal alloys while chromium oxide is formed from base metal alloys.