MDS PREP
What is the primary advantage of using resin cements over other types of cements?
1) Higher compressive strength
2) Improved adhesion to the tooth structure
3) Lower film thickness requirement
4) Faster setting time
Resin cements are known for their excellent adhesion, providing a strong bond to tooth structure and restorative materials.
Maximum shrinkage on firing of ceramic occurs during which stage
1) High bisque
2) Low bisque
3) During condensation
4) None of the above
Dental Materials Answer: 1
Ceramic firing involves a series of processes that transform raw clay
materials into a hard, durable ceramic product. The stages of firing can be
broken down into several steps, but the primary ones are bisque firing and glaze
firing. The bisque firing is done before glazing and is typically the first
firing in the process. The purpose of bisque firing is to remove any remaining
moisture, organic matter, and to harden the ceramic piece to a certain extent,
making it suitable for the application of glazes.
There are two main types of bisque firings:
1. Low bisque: This is a lower temperature firing, usually around 950°C to
1000°C (1742°F to 1832°F). It is used for porous clay bodies and allows for some
shrinkage to occur, but it does not fully vitrify the clay. This stage is often
referred to as the biscuit or bisque stage.
2. High bisque: This is a higher temperature firing, typically between 1000°C to
1150°C (1832°F to 2102°F). It is used for clay bodies that require a higher
degree of vitrification and strength before glazing. At these temperatures, the
clay body experiences significant chemical changes and begins to shrink more
dramatically.
The maximum shrinkage of ceramic occurs during the high bisque stage because the
clay particles undergo a process called vitrification. Vitrification is the
point at which the clay's mineral content starts to melt and fuse together,
creating a glass-like phase within the clay matrix. This results in a stronger,
less porous, and denser material. As the minerals melt and the particles bond,
the overall volume of the material decreases, causing the shrinkage.
The shrinkage rate is influenced by various factors, such as the type of clay,
its composition, water content, and the specific temperature profile of the
firing process. However, it is generally during the high bisque that the most
significant shrinkage occurs. After the high bisque, the subsequent glaze firing
is at a higher temperature, which may cause additional shrinkage, but it is
usually less substantial compared to the initial bisque firing.
Nitinol has the disadvantage of which of the following?
1) It cannot be formed into desired shapes
2) It lacks elastic properties
3) Its strength is not suited for orthodontic purposes
4) It lacks stiffness
Dental Materials Answer: 1
Nitinol is a metal alloy – or mixture – of nickel and titanium. This type of wire is also known as “memory wire” or “smart wire,” and it can be used for braces.
What is the primary concern with using zinc oxide-eugenol cement in large restorations?
1) Low compressive strength
2) Potential for pulpal toxicity
3) High thermal conductivity
4) High solubility
The primary concern is the potential for pulpal toxicity due to the diffusion of eugenol.
What is the typical compressive strength of hardened ZnOE impression paste?
1) 0.4-0.7 MPa
2) 7 MPa
3) 245 MPa
4) 32 MPa
The compressive strength of hardened zinc oxide eugenol (ZnOE) impression paste is generally about 7 MPa, indicating its ability to withstand compressive forces without deformation or failure.
Which of the following is not a type of temporary cementing material?
1) Zinc oxide-eugenol (type III)
2) Calcium hydroxide
3) Glass ionomer cement (type 1)
4) Resin-modified glass ionomer cement
Resin-modified glass ionomer cement is not listed as a type of temporary cementing material in the text.
What is the Threshold Limit Value (TLV) for mercury vapor exposure set by OSHA?
1) 0.01 mg/m3
2) 0.02 mg/m3
3) 0.05 mg/m3
4) 0.1 mg/m3
The TLV for mercury vapor set by OSHA is 0.05 mg/m3.
What is the primary advantage of zinc polycarboxylate cement?
1) High thermal conductivity
2) Low film thickness requirement
3) Chemical bonding with tooth structure
4) Fast setting time
Zinc polycarboxylate cement was formulated to have the strength of zinc phosphate and the biological acceptability of zinc oxide-eugenol cements, with the added advantage of chemical bonding to tooth structure.