AGD Dental Materials and Application 3 — Questions and Answers
Question 1: Which mechanism is responsible for the self-adhesive property of glass ionomer cement to tooth structure?
- Micromechanical interlocking with etched enamel
- Chelation of polyacrylic acid with calcium in hydroxyapatite (Correct answer)
- Hydrophobic monomer penetration into dentinal tubules
- Van der Waals forces with collagen fibers
Correct answer: Chelation of polyacrylic acid with calcium in hydroxyapatite
GIC bonds chemically via chelation between the carboxylate groups of polyacrylic acid and calcium ions in hydroxyapatite, requiring no separate etching step.
Question 2: What is the working time of a dental material most directly influenced by?
- The operator's mixing technique and temperature (Correct answer)
- The patient's oral pH
- The shade of the material
- The light intensity used for curing
Correct answer: The operator's mixing technique and temperature
Working time is primarily affected by mixing technique (spatulation rate/area) and ambient temperature — higher temperatures accelerate the reaction and shorten working time.
Question 3: A flowable composite would be preferred over a packable composite in which clinical situation?
- Class II proximal box in a premolar under heavy occlusal load
- Lining the internal walls of a deep Class I preparation (Correct answer)
- Full-coverage crown cementation
- Anterior incisal edge replacement
Correct answer: Lining the internal walls of a deep Class I preparation
Flowable composites are ideal as liners in cavity preparations due to their low viscosity, easy adaptation, and elastic modulus that provides a stress-absorbing layer.
Question 4: Galvanic corrosion in the mouth is most likely to occur when:
- Two identical alloys are placed in the same quadrant
- Dissimilar metals contact each other in the presence of saliva (Correct answer)
- A base metal crown is placed next to a ceramic crown
- Amalgam is placed under a porcelain veneer
Correct answer: Dissimilar metals contact each other in the presence of saliva
Galvanic corrosion results from electrochemical reactions between dissimilar metals connected through an electrolyte such as saliva, generating a small electric current.
Question 5: Which cement is contraindicated as a final luting agent for porcelain-fused-to-metal crowns due to its high acidity?
- Resin-modified glass ionomer cement
- Zinc phosphate cement (Correct answer)
- Resin cement
- Polycarboxylate cement
Correct answer: Zinc phosphate cement
Zinc phosphate cement's initial low pH (~2) can cause transient pulpal inflammation and is generally considered less biocompatible than newer cements for final cementation.
Question 6: What is the primary reason for applying a dentin bonding agent in multiple coats?
- To increase the depth of the hybrid layer
- To reduce the concentration of solvents and ensure complete monomer coverage (Correct answer)
- To eliminate the need for acid etching
- To increase opacity of the adhesive layer
Correct answer: To reduce the concentration of solvents and ensure complete monomer coverage
Multiple coats ensure complete surface coverage, reduce residual solvent through evaporation, and build a sufficient thickness of adhesive for optimal bonding.
Question 7: Which impression material exhibits the highest tear strength, making it well-suited for recording deep undercuts?
- Addition silicone (VPS)
- Condensation silicone
- Polyether
- Polysulfide rubber (Correct answer)
Correct answer: Polysulfide rubber
Polysulfide rubber (mercaptan) has the highest tear strength among elastomeric impressions, allowing withdrawal from deep undercuts without tearing.
AGD Dental Materials and Application 3
Which mechanism is responsible for the self-adhesive property of glass ionomer cement to tooth structure?