AGD Dental Materials & Technology 3 — Questions and Answers
Question 1: What is the clinical significance of the gel phase during alginate setting?
- Optimal time to remove impression from mouth (Correct answer)
- Material is completely set and dimensionally stable
- Cross-linking has not yet begun
- Syneresis is at its maximum
Correct answer: Optimal time to remove impression from mouth
The gel phase marks when the alginate has set sufficiently for removal — too early causes tearing, too late risks distortion.
Question 2: Which alloy composition is classified as a high-noble metal alloy per ADA specifications?
- ≥25% noble metal by weight
- ≥60% noble metal with ≥40% gold (Correct answer)
- ≥60% noble metal with ≥25% gold
- ≥40% noble metal content
Correct answer: ≥60% noble metal with ≥40% gold
ADA defines high-noble alloys as containing ≥60% noble metals (gold, platinum, palladium) by weight with ≥40% gold specifically.
Question 3: Which property of composite resin is most responsible for postoperative sensitivity?
- Water sorption
- Polymerization shrinkage stress (Correct answer)
- Radiopacity
- Coefficient of thermal expansion
Correct answer: Polymerization shrinkage stress
Polymerization shrinkage creates contraction stress at the tooth-composite interface, disrupting the bond and allowing fluid movement in dentinal tubules.
Question 4: What distinguishes Type IV gypsum (die stone) from Type III gypsum (dental stone)?
- Higher water-to-powder ratio and lower strength
- Lower water-to-powder ratio and higher compressive strength (Correct answer)
- Greater setting expansion
- Faster setting time
Correct answer: Lower water-to-powder ratio and higher compressive strength
Type IV die stone requires less water and yields compressive strengths exceeding 34 MPa, making it suitable for accurate die fabrication.
Question 5: In CAD/CAM dentistry, what is the purpose of the sintering step for zirconia restorations?
- Adding surface glaze
- Converting pre-sintered partially stabilized zirconia to full density and strength (Correct answer)
- Etching the internal surface for bonding
- Applying a shading oxide layer
Correct answer: Converting pre-sintered partially stabilized zirconia to full density and strength
Sintering at 1450–1600°C drives densification of zirconia particles, increasing strength from ~100 MPa to over 900 MPa.
Question 6: Which mechanism allows glass ionomer cement to chemically bond to tooth structure?
- Micromechanical interlocking with etched enamel
- Ionic exchange between polyacid carboxylate groups and calcium in hydroxyapatite (Correct answer)
- Covalent bonding through silane coupling agents
- Van der Waals forces with collagen fibers
Correct answer: Ionic exchange between polyacid carboxylate groups and calcium in hydroxyapatite
Polyacrylic acid chains in GIC chelate with calcium ions in hydroxyapatite, forming an ionic bond directly to enamel and dentin.
Question 7: Which scanning technology used in intraoral scanners captures sequential images to create a 3D digital impression?
- Cone beam computed tomography
- Structured light triangulation and photogrammetry (Correct answer)
- Medical CT scanning
- 2D radiographic stitching
Correct answer: Structured light triangulation and photogrammetry
Most intraoral scanners project structured light patterns onto tooth surfaces and use triangulation algorithms to reconstruct 3D point clouds.
AGD Dental Materials & Technology 3
What is the clinical significance of the gel phase during alginate setting?