MDS PREP
What is the typical mixing ratio for zinc polycarboxylate cement?
1) 1:1
2) 1:2
3) 2:1
4) 3:1
The typical mixing ratio for zinc polycarboxylate cement is 1:2 (powder to liquid).
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.
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 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.
Apart from composites and ceramics, another material that could be copy milled easily and inexpensively is:
1) Molybdenum
2) Germanium
3) Titanium
4) Chromium
Dental Materials Answer: 3
Fabrication of ceramics and metals like titanium that are difficult to cast, is done by CAD-CAM process and copy milling.
What is the optimal force applied during condensation of a 1 mm diameter condenser nib?
1) 3.75 pounds
2) 8.43 pounds
3) 15 pounds
4) 0.04-0.4 µm
The optimal force for condensing a composite resin using a 1 mm diameter condenser nib is 15 pounds, which is within the physiologic limits of the tooth and provides effective condensation.
What is the typical depth of corrosion for most amalgam alloys?
1) 50 to 100 µm
2) 100 to 500 µm
3) 500 to 1000 µm
4) 1000 to 2000 µm
The average depth of corrosion for most amalgam alloys is 100 to 500 µm.
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.