MDS PREP
In which order do elastomeric impression materials rank in terms of tear strength?
1) Condensation silicone > Addition silicone > Polyether > Polysulfide
2) Polysulfide > Condensation silicone > Addition silicone > Polyether
3) Addition silicone > Condensation silicone > Polyether > Polysulfide
4) Polyether > Addition silicone > Condensation silicone > Polysulfide
Polysulfides generally have the highest tear strength among the elastomeric impression materials.
What is the general source of the substance used in irreversible hydrocolloid impression material?
1) Synthetic polymer
2) Plant resin
3) Brown seaweed
4) Petroleum by-product
The material is derived from the structural formula of anhydro-?-d-mannuronic acid, which is extracted from certain types of brown seaweed.
What is the modified form of zinc oxide-eugenol used for temporary cementation?
1) Type I
2) Type II
3) Type III
4) Type IV
The modified form of zinc oxide-eugenol used for temporary cementation is commonly known as Type II due to its lower compressive strength and ease of removal.
Bonding of GIC to tooth structure is brought about by
1) metal ions
2) hydroxyl bond
3) carboxyl bond
4) ionic bond
Dental Materials Answer: 3
one ot the main adanhtges of GIC as a restoratie material was its ability to form chemical bonds with the tooth structure.
Bonding in GIC primarily invokes chelation of carboxyl groups of the polyacids sith the calcium in the apatite of enamel and dentin. Bond rength of enamel is always greater than that of dentin due to higher mineral content. The bonding is improved by the removal of the debris layer called smear layer’ by a process called conditioning.
Which phase in high-copper amalgams is associated with the formation of CuCl23Cu(OH)2 as a corrosion product?
1) The ? (delt1) phase.
2) The ? (gamm1) phase.
3) The ? (epsilon) phase.
4) The ? (zet1) phase.
The n' phase in high-copper amalgams is associated with the formation of CuCl23Cu(OH)2.
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 primary difference between a glass ionomer and a resin-modified glass ionomer cement?
1) Setting time
2) Mechanism of bonding
3) Compressive strength
4) Fluoride release
The primary difference is the presence of resin in resin-modified glass ionomer, enhancing bonding and strength.
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.