ADC Dental Materials Science 1 — Questions and Answers
Question 1: Which property of dental amalgam describes its slow, permanent deformation under sustained compressive load?
- Creep (Correct answer)
- Hardness
- Compressive strength
- Tarnish resistance
Correct answer: Creep
Creep is the time-dependent plastic deformation of amalgam under sustained stress, which can lead to marginal failure if excessive.
Question 2: Delayed expansion in zinc-containing amalgam is primarily caused by:
- Over-trituration of the alloy
- High mercury-to-alloy ratio
- Contamination of the mix with moisture during condensation (Correct answer)
- Under-trituration of the alloy
Correct answer: Contamination of the mix with moisture during condensation
Moisture contamination of zinc-containing amalgam causes a delayed expansion reaction due to hydrogen gas production, which can lead to postoperative pain and restoration failure.
Question 3: Which composite resin type provides the best surface polish due to its very small filler particle size?
- Macrofill composite
- Microfill composite (Correct answer)
- Packable composite
- Flowable composite
Correct answer: Microfill composite
Microfill composites contain colloidal silica particles (0.04–0.4 µm) that allow a very smooth, highly polishable surface, though at the cost of reduced strength.
Question 4: The setting reaction of conventional glass ionomer cement (GIC) is best described as:
- Free-radical polymerization of an acrylic monomer
- Acid-base reaction between polyacrylic acid and fluoroaluminosilicate glass (Correct answer)
- Hydration of calcium silicate phases
- Condensation polymerization releasing water
Correct answer: Acid-base reaction between polyacrylic acid and fluoroaluminosilicate glass
Conventional GIC sets via an acid-base reaction where polyacrylic acid attacks the glass powder, releasing ions that cross-link the polymer chains and harden the cement.
Question 5: Among commonly used luting cements, which has the highest compressive strength?
- Zinc oxide eugenol cement
- Zinc phosphate cement (Correct answer)
- Polycarboxylate cement
- Conventional glass ionomer cement
Correct answer: Zinc phosphate cement
Zinc phosphate cement has the highest compressive strength (~100 MPa) of the classical luting cements, making it suitable for high-stress applications despite its lack of adhesion.
Question 6: The principal clinical advantage of resin-modified glass ionomer cement over conventional glass ionomer cement is:
- Greater total fluoride release over time
- Reduced sensitivity to early moisture contamination and improved early physical properties (Correct answer)
- Significantly lower cost of the material
- Superior biocompatibility with pulp tissue
Correct answer: Reduced sensitivity to early moisture contamination and improved early physical properties
The light-cured resin component in resin-modified GIC allows immediate polymerization, greatly reducing the early moisture sensitivity and improving initial strength compared to conventional GIC.
Question 7: The working time of zinc phosphate cement can be extended by:
- Warming the mixing slab
- Incorporating all powder at once
- Spatulating on a cooled glass slab and adding powder incrementally (Correct answer)
- Using a higher powder-to-liquid ratio
Correct answer: Spatulating on a cooled glass slab and adding powder incrementally
Cooling the glass slab slows the exothermic setting reaction, and incremental powder addition controls the rate of pH rise, together extending the working time to 3–6 minutes.
ADC Dental Materials Science 1
Which property of dental amalgam describes its slow, permanent deformation under sustained compressive load?