Dental Dental Materials 2 — Questions and Answers
Question 1: Which dental cement is considered most biocompatible with the pulp tissue?
- Zinc phosphate cement
- Zinc oxide eugenol (ZOE) cement (Correct answer)
- Polycarboxylate cement
- Resin cement
Correct answer: Zinc oxide eugenol (ZOE) cement
Zinc oxide eugenol cement is highly biocompatible because eugenol has a sedative, obtundent effect on the pulp and the material has a near-neutral pH.
Question 2: What does polymerization shrinkage of composite resin result in clinically?
- Increased fluoride release
- Microleakage and marginal gap formation (Correct answer)
- Improved color stability
- Enhanced surface hardness
Correct answer: Microleakage and marginal gap formation
As composites shrink toward the light source during polymerization, gaps can form at the restoration margins, leading to microleakage and potential secondary caries.
Question 3: What is the primary advantage of polyvinyl siloxane (PVS) impression material over polysulfide?
- Lower cost
- Superior dimensional accuracy and stability (Correct answer)
- Faster setting time
- Better tear resistance
Correct answer: Superior dimensional accuracy and stability
PVS impressions are highly dimensionally accurate and stable, allowing casts to be poured days after the impression is taken without significant distortion.
Question 4: Which type of dental porcelain is fused directly to a metal substructure in a PFM crown?
- Feldspathic porcelain (Correct answer)
- Leucite-reinforced porcelain
- Zirconia porcelain
- Lithium disilicate porcelain
Correct answer: Feldspathic porcelain
Feldspathic porcelain is the traditional veneering porcelain used in PFM restorations because it bonds well to the metal oxide layer on the substructure.
Question 5: Increasing the water-to-powder ratio of a gypsum mix will have which effect on the set product?
- Increased strength and decreased setting expansion
- Decreased strength and decreased setting time
- Decreased strength and increased setting time (Correct answer)
- Increased setting expansion and increased strength
Correct answer: Decreased strength and increased setting time
Excess water dilutes the reaction, slowing setting time and leaving more porosity in the set material, resulting in reduced compressive strength.
Question 6: What is the purpose of the smear layer removal (etching) step in total-etch bonding systems?
- To sterilize the dentin surface
- To remove debris and open dentinal tubules for resin tags and hybridization (Correct answer)
- To bleach the dentin for better color match
- To harden the dentin before bonding
Correct answer: To remove debris and open dentinal tubules for resin tags and hybridization
Acid etching removes the smear layer and demineralizes superficial dentin, creating microporosities for resin infiltration and a hybrid layer for micromechanical bonding.
Question 7: Which property of dental wax makes it suitable for use in bite registration?
- High thermal conductivity
- Plasticity at mouth temperature and rigidity at room temperature (Correct answer)
- Chemical adhesion to enamel
- High tensile strength
Correct answer: Plasticity at mouth temperature and rigidity at room temperature
Bite registration wax softens at oral temperature to record occlusal relationships accurately and then hardens at room temperature to preserve the registration.
Dental Dental Materials 2
Which dental cement is considered most biocompatible with the pulp tissue?