NBDHE NBDHE Dental Materials and Procedures 2 — Questions and Answers
Question 1: Which type of gypsum product has the highest compressive strength and is used for dies?
- Plaster of Paris
- Dental stone
- Die stone (Type IV) (Correct answer)
- Orthodontic stone
Correct answer: Die stone (Type IV)
Type IV die stone has the highest compressive strength and lowest setting expansion, making it ideal for accurate die fabrication.
Question 2: What is the primary advantage of using polyvinyl siloxane (PVS) impression material over polysulfide?
- Lower cost
- Greater dimensional stability over time (Correct answer)
- Faster set time only
- Better compatibility with latex gloves
Correct answer: Greater dimensional stability over time
PVS impression materials are addition silicones that exhibit excellent dimensional stability and can be poured multiple times without significant distortion.
Question 3: When cementing a metal crown with zinc phosphate cement, why must the tooth be kept dry?
- Moisture increases setting time
- Moisture weakens the cement film strength
- Moisture causes discoloration
- Moisture increases solubility in oral fluids (Correct answer)
Correct answer: Moisture increases solubility in oral fluids
Moisture contamination increases the solubility of zinc phosphate cement in oral fluids, reducing the longevity of the restoration.
Question 4: Which dental alloy classification contains at least 25% gold and is used for crowns requiring high strength?
- Type I
- Type II
- Type III
- Type IV (Correct answer)
Correct answer: Type IV
Type IV gold alloy has the highest hardness and strength due to its composition, making it suitable for thin restorations like inlays, partial denture frameworks, and clasps.
Question 5: What causes the 'orange peel' surface texture sometimes seen on processed acrylic denture bases?
- Too much monomer in the mix
- Premature closure of the flask
- Rapid initial cooling of the flask
- Insufficient pressure during processing (Correct answer)
Correct answer: Insufficient pressure during processing
Insufficient pressure during processing allows porosity to develop at the surface, creating the characteristic orange peel appearance.
Question 6: Which property of dental wax makes it suitable for use in bite registration procedures?
- High flow at room temperature
- Minimal flow at body temperature and brittleness at room temperature (Correct answer)
- High thermal conductivity
- Low melting point below 37°C
Correct answer: Minimal flow at body temperature and brittleness at room temperature
Bite registration waxes are formulated to have minimal flow at body temperature so they accurately record the occlusal relationship without distortion.
Question 7: A patient's composite restoration shows staining at the margins after 2 years. What material property is most responsible?
- High coefficient of thermal expansion
- Microleakage due to polymerization shrinkage (Correct answer)
- Excessive filler particle size
- Low hardness of the matrix resin
Correct answer: Microleakage due to polymerization shrinkage
Polymerization shrinkage creates gaps at the tooth-restoration interface, allowing microleakage that leads to marginal staining and secondary caries.
NBDHE NBDHE Dental Materials and Procedures 2
Which type of gypsum product has the highest compressive strength and is used for dies?