MDS PREP
What is the typical particle size of silica in microfilled composites?
1) 0.5-1 µm.
2) 0.04-0.2 µm.
3) 1-10 µm.
4) 10-30 µm.
Microfilled composites have a very high surface area with silica particles diameters of 0.04 to 0.2 µm, which provides excellent aesthetic results and polishability.
What is the ANSI/ADA Specification No. 96 (ISO 9917) minimum compressive strength for luting cement?
1) 50 MPa
2) 70 MPa
3) 100 MPa
4) 150 MPa
The ANSI/ADA Specification No. 96 (ISO 9917) stipulates a minimum 24-hour compressive strength of 70 MPa for standard luting consistency dental cement.
What is the primary function of 2-hydroxyethyl methacrylate (HEMA) in dentinal bonding?
1) To act as an initiator for the polymerization reaction
2) To create a hydrophobic barrier between dentin and resin
3) To dissolve the dentin surface
4) To create a hydrophilic bridge between the dentin and resin
HEMA is a hydrophilic monomer that is applied to the conditioned dentin. It fills the dentinal tubules and adheres to the exposed collagen fibers, creating a wetting layer that allows subsequent hydrophobic resins to infiltrate and bond to the dentin. This bridging action is crucial for the adhesion of resin to the hydrophilic dentin surface, which is essential for the longevity and durability of the restoration.
What is the pH of zinc polycarboxylate cement after 28 days?
1) 2.8
2) 3.7
3) 5.2
4) 5.8
The pH values provided in the text indicate that zinc polycarboxylate cement reaches a pH of 5.8 after 28 days.
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.
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.
The opacity in ceramics is achieved by adding
1) Boric oxide
2) Copper oxide
3) Silica
4) Titanium oxide
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.