AGD Dental Materials and Application 5 — Questions and Answers
Question 1: What is the primary clinical advantage of self-adhesive resin cements (e.g., RelyX Unicem) over conventional resin cements?
- Higher film thickness allows better marginal seal
- They eliminate the need for separate etching and priming steps (Correct answer)
- They provide superior bond strength to enamel
- They are radiolucent for easy radiographic evaluation
Correct answer: They eliminate the need for separate etching and priming steps
Self-adhesive resin cements contain acidic monomers that simultaneously etch, prime, and bond to tooth structure in a single step, simplifying the luting procedure.
Question 2: During amalgam condensation, why is it important to use small-diameter condensers and apply firm pressure?
- To increase the mercury content for improved flow
- To adapt the material to cavity walls and eliminate voids (Correct answer)
- To accelerate the gamma-2 phase formation
- To increase the setting expansion of the amalgam
Correct answer: To adapt the material to cavity walls and eliminate voids
Small condensers with firm pressure adapt amalgam to all cavity walls, eliminate internal voids that weaken the restoration, and ensure intimate contact with the preparation.
Question 3: A patient receives a new ceramic crown that feels high in occlusion. The dentist adjusts it intraorally with a diamond bur. What must be done next?
- Polish with fine grit rubber points and apply a fluoride varnish
- Re-fire the crown in a porcelain oven to restore glaze
- Repolish with diamond polishing paste and a felt disk (Correct answer)
- Apply bonding agent to the adjusted surface
Correct answer: Repolish with diamond polishing paste and a felt disk
Intraoral adjustment with a diamond bur destroys the glaze and creates surface roughness; repolishing with diamond paste restores smoothness and reduces wear of opposing teeth.
Question 4: The Shore A hardness scale is most commonly used to measure the hardness of:
- Dental casting alloys
- Ceramic restorations
- Dental elastomers and soft denture liners (Correct answer)
- Amalgam restorations
Correct answer: Dental elastomers and soft denture liners
Shore A hardness measures the hardness of soft, rubbery materials including elastomeric impression materials, soft denture liners, and occlusal splints.
Question 5: Which property differentiates addition silicone (VPS) from condensation silicone impression materials?
- Addition silicone releases alcohol as a byproduct, causing dimensional change
- Addition silicone has no byproduct and exhibits superior dimensional stability (Correct answer)
- Condensation silicone offers better detail reproduction
- Condensation silicone has a longer shelf life
Correct answer: Addition silicone has no byproduct and exhibits superior dimensional stability
Addition silicone cross-links without releasing byproducts, resulting in virtually zero dimensional change, which is why it is the gold standard for precision impressions.
Question 6: Which base material placed under a deep restoration primarily serves to stimulate reparative dentin formation?
- Zinc phosphate cement
- Calcium hydroxide (Correct answer)
- Glass ionomer cement
- Zinc oxide eugenol cement
Correct answer: Calcium hydroxide
Calcium hydroxide (Ca(OH)2) has a high pH (~12) that stimulates odontoblasts or undifferentiated cells to form reparative (tertiary) dentin when placed near the pulp.
Question 7: What is the main reason for using a rubber dam during composite resin placement?
- To improve the curing light's penetration depth
- To prevent moisture contamination that inhibits adhesive bonding (Correct answer)
- To reduce the composite's polymerization shrinkage
- To increase the working time of the adhesive system
Correct answer: To prevent moisture contamination that inhibits adhesive bonding
Saliva and crevicular fluid contaminate the bonded surfaces, disrupting the hybrid layer and dramatically reducing composite resin bond strength.
AGD Dental Materials and Application 5
What is the primary clinical advantage of self-adhesive resin cements (e.g., RelyX Unicem) over conventional resin cements?