AGD Dental Materials & Technology 5 — Questions and Answers
Question 1: Which surface treatment is required before bonding resin cement to a lithium disilicate ceramic restoration?
- Sandblasting with aluminum oxide only
- Hydrofluoric acid etching followed by silane application (Correct answer)
- Phosphoric acid etching followed by primer
- No surface treatment — bonding is achieved by pressure alone
Correct answer: Hydrofluoric acid etching followed by silane application
HF acid etches the glassy matrix of lithium disilicate creating a microtextured surface; silane then chemically bridges the ceramic to the resin cement.
Question 2: What does the term 'tack cure' describe in the placement of resin composite?
- Full cure using extended light exposure
- Brief light exposure to partially polymerize and stabilize material for contouring before final cure (Correct answer)
- Thermally-activated polymerization step
- Chemical cure initiation without light
Correct answer: Brief light exposure to partially polymerize and stabilize material for contouring before final cure
A tack cure (2–3 seconds) creates enough polymerization to hold the composite shape during contouring while allowing further manipulation before the final full cure.
Question 3: Which thermoplastic polymer is most commonly used for clear aligner fabrication?
- Polycarbonate
- Polyethylene terephthalate glycol (PETG) (Correct answer)
- Polymethyl methacrylate (PMMA)
- Polypropylene
Correct answer: Polyethylene terephthalate glycol (PETG)
PETG offers the combination of clarity, stiffness, and thermoformability needed for accurate aligner fabrication with good force delivery characteristics.
Question 4: A patient's amalgam restoration shows a bluish-gray discoloration of adjacent tooth structure. What is the most likely cause?
- Microleakage and secondary caries staining
- Corrosion products from amalgam diffusing into dentinal tubules (Correct answer)
- Hypocalcification of the tooth structure
- Staining from dietary sources through the restoration margin
Correct answer: Corrosion products from amalgam diffusing into dentinal tubules
Corrosion byproducts (sulfides and oxides) from dental amalgam diffuse into dentinal tubules over time, causing the characteristic 'amalgam tattoo' effect in tooth structure.
Question 5: What is the recommended storage condition for vinyl polysiloxane (VPS) impression materials to preserve accuracy?
- Refrigerate at 4°C until immediately before use
- Store at room temperature away from heat and latex gloves (Correct answer)
- Keep frozen until the day of use
- Store in a humid environment to prevent dehydration
Correct answer: Store at room temperature away from heat and latex gloves
VPS should be stored at room temperature; refrigeration slows setting but latex contamination from gloves irreversibly inhibits polymerization at the surface.
Question 6: What property makes polyether impression materials particularly advantageous in patients with copious saliva?
- They are highly hydrophobic and repel moisture
- They are inherently hydrophilic and set accurately in the presence of moisture (Correct answer)
- They chemically bond to the saliva proteins
- They have the longest working time of all elastomers
Correct answer: They are inherently hydrophilic and set accurately in the presence of moisture
Polyether's hydrophilic nature allows it to displace moisture from tooth surfaces and achieve accurate impressions even in a wet field.
Question 7: Which parameter of light-curing units (LCUs) most directly determines the rate of photoinitiator activation in resin composites?
- Duration of cure cycle in seconds
- Irradiance (intensity) measured in mW/cm² (Correct answer)
- Distance from tip to restoration surface
- Color temperature of the light source
Correct answer: Irradiance (intensity) measured in mW/cm²
Irradiance (mW/cm²) determines the number of photons delivered per unit area per second, which directly controls the rate of camphorquinone or alternative photoinitiator activation.
AGD Dental Materials & Technology 5
Which surface treatment is required before bonding resin cement to a lithium disilicate ceramic restoration?