MDS PREP
Brinnel hardness number of a dental gold alloy is directly proportional to its:
1) Tensile strength
2) Elongation
3) Modulus of elasticity
4) Modulus of resiLience
Dental Materials Answer: 1
Brinnel and Rockwell tests are cLassified as macrohardness tests and they aie not suitable for brittle materials.
The Knoop and Vickers tests are classified as microhardness tests. Both of these tests employ toads less than 9.8N.
The Shore and the Barcot tests are used for measuring the hardness of rubbers and plastics.
The Bnnnel test is the one of oldest tests used for determining the hardness of materials and is directly related to proportional limit and the ultimate tensile strength of dental gold alloys.
The convenience of the Rockwell test, with direct reading of the depth of the indentation, has lead to its wide usage.
The Knoop hardness test is used to obtain the values for both exceedingly hard and soft materials. The hardness value is independent of the ductility of the material.
The Vickers test is employed for dental costing gold alloys. It is suitable for determining the hardness of brittle materials.
What is the main component of zinc oxide-eugenol cement?
1) Zinc oxide
2) Silica
3) Phosphoric acid
4) Polycarboxylate acid
Zinc oxide-eugenol cement is primarily composed of zinc oxide and eugenol.
What is the typical range of Charpy impact strength for a heat-activated denture resin?
1) 0.48 to 0.78 joules
2) 0.98 to 1.27 joules
3) There is no typical range provided
4) The information is not relevant to heat-activated resins
Heat-activated denture resins typically have a Charpy impact strength range of 0.98 to 1.27 joules, which is higher than that of chemically activated resins.
What is the typical particle size range of the fillers in conventional, microfilled, and hybrid composites?
1) Conventional: 8-12 µm, Microfilled: 0.04-0.4 µm, Hybrid: 0.1-0.01 µm
2) Conventional: 1-5 µm, Microfilled: 0.04-0.4 µm, Hybrid: 0.01-0.1 µm
3) Conventional: 8-12 µm, Microfilled: 0.01-0.05 µm, Hybrid: 0.5-1 µm
4) Conventional: 0.01-0.1 µm, Microfilled: 0.1-0.5 µm, Hybrid: 0.5-1 µm
The particle size of the fillers in composite materials affects their physical and handling properties. Conventional composites have larger filler particles, while microfilled and hybrid composites have smaller ones. The text provides the typical ranges for each type of composite.
What is the typical setting time range for Type II (Normal set) alginate impression material?
1) 1-2 minutes
2) 2-4 minutes
3) 4-6 minutes
4) 6-8 minutes
Type II (Normal set) alginate impression material has a setting time of 2-4 minutes, which is longer than the fast-setting Type I material.
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 purpose of using a temporary cement?
1) To provide a permanent seal
2) To allow for temporary fixation before the final restoration is placed
3) To strengthen the tooth structure
4) To fill gaps caused by caries
Temporary cements are used to hold a temporary restoration in place until the final restoration can be placed, and they should have a lower compressive strength to allow for easy removal.
What is the typical pH of zinc polycarboxylate cement immediately after mixing?
1) Less than 2
2) Between 2 and 4
3) Between 4 and 7
4) Greater than 7
The pH is mentioned to be around 2.8 after 3 minutes, which indicates an acidic nature initially.