INBDE Restorative Dentistry and Dental Materials 1 — Questions and Answers
Question 1: Which property of dental composite resins is most responsible for post-operative sensitivity?
- Thermal expansion coefficient mismatch
- Polymerization shrinkage creating gap formation (Correct answer)
- Lack of fluoride release
- Hydrolytic degradation
Correct answer: Polymerization shrinkage creating gap formation
Polymerization shrinkage (1–5% volumetric) creates contraction stress at the bonded margins, leading to gap formation and post-operative sensitivity.
Question 2: Amalgam's strength is primarily derived from which phase?
- Gamma phase (unreacted silver-tin)
- Gamma-1 phase (silver-mercury) (Correct answer)
- Gamma-2 phase (tin-mercury)
- Delta phase (copper-tin)
Correct answer: Gamma-1 phase (silver-mercury)
The gamma-1 phase (Ag2Hg3) is the matrix phase that gives amalgam its strength, while gamma-2 (Sn7-8Hg) is the weakest and most corrosion-prone phase.
Question 3: Dental porcelain is classified as a ceramic primarily because it contains:
- Metal oxides only
- Inorganic non-metallic crystalline or glass materials (Correct answer)
- Organic polymer matrix
- Zinc phosphate cement
Correct answer: Inorganic non-metallic crystalline or glass materials
Ceramics are inorganic, non-metallic materials; dental porcelain is primarily composed of silica, feldspar, and alumina in a glass matrix.
Question 4: The retention of a full-crown preparation is most influenced by:
- Occlusal reduction amount
- Taper of the axial walls (convergence angle) (Correct answer)
- Margin design (chamfer vs feather edge)
- Surface roughness of the preparation
Correct answer: Taper of the axial walls (convergence angle)
Axial wall taper (convergence angle) is the most critical retention factor; ideally 6–10° total occlusal convergence maximizes both retention and withdrawal path.
Question 5: Glass ionomer cement bonds to tooth structure primarily through:
- Micromechanical retention via etching
- Ionic bonding to calcium in hydroxyapatite (Correct answer)
- Van der Waals forces
- Chemical bonding to collagen
Correct answer: Ionic bonding to calcium in hydroxyapatite
Glass ionomer cement bonds chemically to tooth structure via ionic interactions between its polyacrylic acid component and calcium and phosphate in hydroxyapatite.
Question 6: Which composite placement technique best minimizes polymerization shrinkage stress?
- Bulk fill technique
- Horizontal incremental placement
- Diagonal incremental placement
- Oblique incremental placement (Correct answer)
Correct answer: Oblique incremental placement
Oblique (diagonal) incremental placement reduces the C-factor (ratio of bonded to unbonded surfaces) and allows shrinkage stress relief as each increment cures.
INBDE Restorative Dentistry and Dental Materials 1
Which property of dental composite resins is most responsible for post-operative sensitivity?