MDS PREP
Gypsum Bonded Investment should NOT be heated above
1) 700°C
2) 750°C
3) 800°C
4) 900°C
Dental Materials Answer: 1
What is the function of a light source in photopolymerization of dental composites?
1) To generate heat for setting.
2) To activate the photosensitizer and initiate the polymerization reaction.
3) To cure the material by chemical reaction.
4) To improve the aesthetics of the restoration.
The light source is crucial in the photopolymerization process as it activates the photosensitizer, usually camphorquinone, which in turn generates free radicals that initiate the polymerization of the resin.
How does the presence of the ?2 phase affect the corrosion resistance of high-copper amalgams?
1) It significantly increases the corrosion resistance.
2) It has no effect on the corrosion resistance.
3) It significantly decreases the corrosion resistance.
4) It is the most corrodible phase in high-copper amalgams.
The ?2 phase is the least corrosion-resistant phase in high-copper amalgams.
What is the typical concentration range for an amine initiator like DMAEMA in a dental composite resin?
1) 0.1-0.2 wt%.
2) 0.5-1.0 wt%.
3) 1-2 wt%.
4) 2-5 wt%.
An aliphatic amine like DMAEMA is used at low concentrations (around 0.15 wt%) in composite resins to initiate the free radical polymerization in the presence of the light-sensitive initiator, such as camphorquinone.
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.
Polyethers are susceptible to dimensional change if immersed for a long time. The recommended maximum time to immerse in disinfectant is
1) 1 minute
2) 10 minutes
3) 30 minutes
4) 1 hour
Dental Materials Answer: 2
The polyethers are susceptible to dimensional change if immersed for a long time (>10 min) because of their pronounced hydrophilic nature.
The essential ingredient of dental inlay investment are :
1) Quartz, cristobalite
2) β hemihydrate
3) α hemihydrate
4) Ammonium phosphate
Dental Materials Answer: 3
The essential ingredients of the dental inlay investment employed with the conventional gold casting alloys are a-hemihydrate of gypsum, quartz, or cristobalite, which are allotropic forms of silica.
What is the primary wavelength emitted by an argon laser used in dentistry?
1) 400-500 nm.
2) 500-600 nm.
3) 800-900 nm.
4) 1000-1100 nm.
Argon lasers emit light in the green-blue spectrum, with wavelengths between 488 and 514.5 nm, which are absorbed well by pigmented tissues like hemoglobin and melanin, making them useful for soft tissue procedures.