MDS PREP
What are microfilled composites known for?
1) Their high wear resistance.
2) Their high translucency.
3) Their ease of manipulation.
4) Both A and B.
Microfilled composites contain very fine silica particles (0.04 to 0.2 µm in diameter), which give them excellent translucency and a high surface area for better filling of small restorations.
Which type of composite has a filler particle size of 8-12 µm?
1) Microfilled composite
2) Small particle composite
3) Conventional composite
4) Hybrid composite
Conventional composites have a filler particle size of 8-12 µm. Microfilled composites have smaller particles (0.04-0.4 µm), small particle composites have intermediate sizes (1-5 µm), and hybrid composites have even smaller sizes (0.1-0.01 µm).
What is the typical pH of a resin cement immediately after mixing?
1) Less than 2
2) Between 2 and 4
3) Between 4 and 7
4) Greater than 7
The pH of resin cements is usually slightly acidic after mixing, subject to variation in formulation.
The function of 2% potassium sulphate in a gypsum product is
1) to regulate the setting expansion.
2) to regulate the setting time.
3) to act as a retarder.
4) none of the above.
Dental Materials Answer: 4
Sodium chloride is an accelerator up to about 2% of the hemihydrates, but at a higher concentration, it acts as a retarder. Sodium sulphate has its maximum acceleration effect at approximately 3.4%; at greater concentrations, it becomes a retarder.
The most commonly used accelerator is potassium sulphate. It is particularly effective in concentrations higher than 2% since the reaction product. which seems to be syngenite (K,Ca[SO4].H1O) crystallizes rapidly. Many soluble sulphates act as accelerators, whereas powdered gypsum (calcium sulphate dehydrate) accelerates the setting rate, because the
particles act as nuclei of crystallization.
Citrates. acetates and borates generally retard the reaction.
What is the primary component of zinc polycarboxylate cement?
1) Zinc oxide
2) Polyacrylic acid
3) Titanium dioxide
4) Calcium hydroxide
Zinc polycarboxylate cement primarily consists of zinc oxide and polyacrylic acid.
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.
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.
Hardness number which does not depend on the ductility of metal
1) KHN
2) VHN
3) RHN
4) BHN
Dental Materials Answer: 1
Knoop hardness test - Diamond of rhombic shape (The long axis of indentotion is measured)
Vickers (Diamond pyramid test) - Diamond of square base shape (The diagonal length of the indentation is measured)
Rockwell - Diamond of conical shape (The penetration depth is measured)
Brinells - Steel ball (The diameter of indentation is measured)
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.