NBDHE NBDHE Dental Materials and Procedures 3 — Questions and Answers
Question 1: Which component of composite resin is responsible for coupling the filler particles to the resin matrix?
- Photoinitiator (camphorquinone)
- Silane coupling agent (Correct answer)
- BIS-GMA monomer
- Diluent monomer (TEGDMA)
Correct answer: Silane coupling agent
The silane coupling agent chemically bonds the inorganic filler particles to the organic resin matrix, improving the mechanical properties of the composite.
Question 2: What is the primary reason that bonding agents are applied in multiple coats when using total-etch technique?
- To increase the thickness of the hybrid layer
- To ensure adequate wetting and penetration of all etched surfaces
- To compensate for oxygen inhibition of the outer layer (Correct answer)
- To reduce postoperative sensitivity
Correct answer: To compensate for oxygen inhibition of the outer layer
The outermost layer of bonded resin remains uncured due to oxygen inhibition, so multiple coats ensure a fully polymerized bonding layer beneath.
Question 3: Galvanic shock between two dissimilar metals in the mouth occurs due to which electrochemical process?
- Oxidation of the nobler metal
- Reduction of the less noble metal
- Current flow from the less noble to the nobler metal through the electrolyte (Correct answer)
- Corrosion of the nobler metal at the cathode
Correct answer: Current flow from the less noble to the nobler metal through the electrolyte
When two dissimilar metals contact in saliva (an electrolyte), current flows from the less noble (anode) to the nobler metal (cathode), causing the patient to feel a galvanic shock.
Question 4: When using alginate impression material, what is the effect of using warmer water during mixing?
- Increases working time
- Decreases setting time (Correct answer)
- Increases flexibility of the set impression
- Decreases tear strength
Correct answer: Decreases setting time
Warmer water accelerates the chemical reaction in alginate, decreasing the setting time and reducing the working time available to the clinician.
Question 5: Which cement is most biocompatible and has the ability to release fluoride, making it ideal under restorations near the pulp?
- Zinc oxide eugenol (ZOE)
- Zinc phosphate cement
- Glass ionomer cement (Correct answer)
- Calcium hydroxide (Dycal)
Correct answer: Glass ionomer cement
Glass ionomer cement releases fluoride, has good biocompatibility, and bonds chemically to tooth structure, making it an excellent liner or base near the pulp.
Question 6: What is the purpose of the 'sand blasting' (air abrasion) step when bonding to metal surfaces of a PFM restoration?
- To remove the oxide layer and increase micromechanical retention (Correct answer)
- To apply a silane coupling agent
- To increase the metal's corrosion resistance
- To reduce the surface hardness for better bonding
Correct answer: To remove the oxide layer and increase micromechanical retention
Air abrasion with aluminum oxide removes surface contaminants and creates micromechanical retention by roughening the metal surface prior to bonding.
Question 7: A denture processed using the compression molding technique shows internal porosity. What is the most likely cause?
- Too little monomer in the dough
- Insufficient curing time at 74°C
- Processing at too high a temperature causing boiling of monomer (Correct answer)
- Using Type II acrylic resin instead of Type I
Correct answer: Processing at too high a temperature causing boiling of monomer
If the processing temperature exceeds 100°C, the residual monomer (boiling point ~100.3°C) vaporizes and creates internal gaseous porosity in the acrylic.
NBDHE NBDHE Dental Materials and Procedures 3
Which component of composite resin is responsible for coupling the filler particles to the resin matrix?