MDS PREP
Which of the following is not true about casting gypsum-bonded investment material?
1) Its used for cast metal alloys
2) 50—65% of gypsum changes to form α-hemihydrate
3) The investment material is not heated above 700°C temperature
4) Heating above 700°C causes formation of sulphur dioxide from copper sulphate
Dental Materials Answer: 1
Gypsum-bonded investments are used for gold alloys. The essential ingredients of the dental inlay investment employed with the conventional gold casting alloys are α-hemihydrate of gypsum, quartz or cristobalite. which are allotropic forms of silica.
Ist investments flow contain the α-hemihydrate of gypsum. because greater strength is obtained. This gypsum
product serves as a binder to hold other ingredients together and provide rigidity. The strength of the investment is dependent on the amount of binder present.
A slight expansion takes place between 400°C and approximately 700°C (1292°F). and then a large contraction occurs. This later shrinkage is most likely caused by decomposition and release of sulphur gases, such as sulphur dioxide.
This decomposition not only causes shrinkage but also contaminates the casting with the sulphides of the nonnohlc alloying elements, such as silver and copper. Thus, it is imperative that gypsum investments should not be heated above 700°C (1292°F). however, for gypsum products containing carbon, the maximum temperature should be 650°C (1202°F). In this way, proper ut and uncontaminated alloys are obtained.
What is the typical range of pH for acidic dental cements?
1) pH > 7
2) pH 7-10
3) pH 4-7
4) pH < 4
Acidic dental cements typically have a pH less than 7.
Which type of amalgam alloy has the lowest compressive strength at 1 hour?
1) High-copper lathe-cut alloy
2) Low-copper lathe-cut alloy
3) High-copper spherical alloy
4) Low-copper spherical alloy
The compressive strength at 1 hour is lowest for the low-copper lathe-cut alloy, which is 45 MPa.
What is the primary advantage of resin teeth over porcelain teeth in terms of impact resistance and ductility?
1) Resin teeth are more likely to chip or fracture.
2) Resin teeth have better dimensional stability.
3) Resin teeth have greater wear resistance.
4) Resin teeth are less likely to chip or fracture.
Resin teeth are more ductile than porcelain teeth, which means they can absorb and distribute forces better, making them less prone to chipping or fracturing on impact.
How does the degree of polymerization affect the strength of resin?
1) There is no correlation between the two
2) Higher degree of polymerization results in increased strength
3) Lower degree of polymerization results in increased strength
4) The strength is unaffected by the degree of polymerization
A higher degree of polymerization in resins generally correlates with greater strength, as more polymer chains are formed and cross-linked.
How does the concentration of mercury in urine relate to neurological changes?
1) Neurological changes are detected at urine mercury levels of 1 µg/L.
2) Neurological changes are detected at urine mercury levels of 10 µg/L.
3) Neurological changes are detected at urine mercury levels of 500 µg/L.
4) There is no established link between mercury concentration in urine and neurological changes.
Neurological changes are not detected until urine mercury levels exceed 500 µg/L, which is significantly higher than the levels associated with amalgam placement.
What type of dental cement is used in cases of rampant caries and unhygienic oral conditions?
1) Zinc polyacrylate
2) Calcium sulfate
3) Zinc oxide-eugenol
4) Calcium hydroxide
Calcium hydroxide is used in cases of rampant caries and unhygienic oral conditions due to its antibacterial and tissue-dissolving properties.
What happens to the strength of irregularly shaped amalgam alloys when they are over-triturated?
1) It significantly increases.
2) It significantly decreases.
3) It remains the same.
4) It first increases and then decreases.
The strength of irregularly shaped amalgam alloys increases with over-trituration.