MDS PREP
What is the typical polymerization shrinkage of Bis-GMA?
1) 1-2%.
2) 3-4%.
3) 5-6%.
4) 5%.
Bis-GMA undergoes a free radical addition polymerization reaction with a shrinkage of about 1-2%, forming a highly rigid cross-linked setting material.
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.
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 role of MDPB in dental composites?
1) It provides improved mechanical properties.
2) It acts as an initiator for the polymerization reaction.
3) It enhances the antibacterial activity of the composite material.
4) It reduces the viscosity of the resin.
MDPB (methacryloxy decyl pyridinium bromide) is a quaternary ammonium salt that has been shown to be effective against various streptococci in dental composites. Its inclusion enhances the antibacterial properties of the material.
What is the preferred method of degassing for powered gold restorations?
1) An alcohol flame
2) An oxygen-acetylene flame
3) A butane flame
4) A nitrogen-hydrogen flame
The preferred method for degassing powered gold restorations is the use of an alcohol flame, specifically one that is a clean blue flame from absolute or 90% ethyl/methyl alcohol. The material is held in the flame until it reaches a dull red glow, which typically takes 15-20 seconds. This process removes any trapped air or volatile components that could compromise the integrity of the restoration.
What happens if the water temperature exceeds 50°C during the mixing of gypsum products?
1) The setting reaction is accelerated.
2) The setting reaction is retarded.
3) No reaction occurs.
4) The material becomes less soluble.
If the temperature of the water used to mix gypsum products exceeds 50°C, it can slow down the setting reaction due to the reversible nature of the gypsum crystal formation at higher temperatures.
Which type of composite has a filler particle size of 8-12 µm?
1) Microfilled composite
2) Small particle composite
3) Conventional composite
4) Hybrid composite
Conventional composites have a filler particle size of 8-12 µm. Microfilled composites have smaller particles (0.04-0.4 µm), small particle composites have intermediate sizes (1-5 µm), and hybrid composites have even smaller sizes (0.1-0.01 µm).
What is the most corrodible phase in the low-copper amalgam system?
1) Sn7. Hg
2) ? (gamm1) phase
3) Cu3Sn phase
4) ? (delt1) phase
The Sn7. Hg or ? (gamm1) phase is the most corrodible in the low-copper amalgam system.