AGD Dental Materials and Biomaterials 5 — Questions and Answers
Question 1: Which resin monomer is most commonly used as the base in contemporary dental adhesive systems due to its bifunctional nature?
- TEGDMA
- Bis-GMA (Correct answer)
- UDMA
- HEMA
Correct answer: Bis-GMA
Bis-GMA (bisphenol A-glycidyl methacrylate) is the most widely used base monomer, providing high strength and stiffness via its rigid aromatic backbone.
Question 2: A dentist uses a 10-MDP-based adhesive. What is the primary benefit of 10-MDP over earlier phosphate ester monomers?
- Greater water compatibility
- Strong ionic bond to hydroxyapatite calcium that resists hydrolysis (Correct answer)
- Higher film thickness for gap sealing
- Elimination of the need for acid etching
Correct answer: Strong ionic bond to hydroxyapatite calcium that resists hydrolysis
10-MDP forms stable calcium salt bonds with hydroxyapatite that are highly resistant to hydrolytic degradation, improving long-term bond durability.
Question 3: Bulk-fill composites are formulated to allow curing depths of 4–5 mm primarily through which modification?
- Higher photoinitiator concentration and modified translucency (Correct answer)
- Reduced filler content
- Elimination of Bis-GMA
- Use of self-cure activators only
Correct answer: Higher photoinitiator concentration and modified translucency
Bulk-fill composites use optimized photoinitiator systems and increased translucency so the curing light penetrates deeper, achieving adequate conversion at 4–5 mm.
Question 4: The elastic modulus of a restorative material is most important when matching it to:
- The color of adjacent teeth
- The stiffness of the surrounding tooth structure to distribute stress (Correct answer)
- The patient's bite force alone
- The setting shrinkage requirements
Correct answer: The stiffness of the surrounding tooth structure to distribute stress
Matching the elastic modulus of a restorative to surrounding tooth structure prevents stress concentration at the interface under load.
Question 5: Which impression material is contraindicated in a patient with a severe latex allergy even when using non-latex gloves?
- Polyvinylsiloxane (addition silicone)
- Polysulfide rubber base (Correct answer)
- Polyether
- Irreversible hydrocolloid (alginate)
Correct answer: Polysulfide rubber base
Polysulfide (rubber base) impression materials contain latex-related compounds and should be avoided in latex-allergic patients regardless of glove choice.
Question 6: In a CAD/CAM milled zirconia crown, what post-milling procedure is essential to achieve final hardness and translucency?
- Glazing with porcelain slurry
- High-temperature sintering (Correct answer)
- Sandblasting and silane treatment
- Low-fusing ceramic application
Correct answer: High-temperature sintering
Pre-sintered zirconia is soft and machinable; high-temperature sintering (~1500°C) densifies the material, achieving full hardness and desired translucency.
Question 7: Which property of bioactive glass (Bioglass) makes it suitable for use in bone and dentin regeneration procedures?
- Extreme chemical inertness
- Formation of a hydroxyapatite layer that bonds to hard tissue (Correct answer)
- High elastic modulus matching enamel
- Radiopacity comparable to amalgam
Correct answer: Formation of a hydroxyapatite layer that bonds to hard tissue
Bioactive glass reacts with physiologic fluids to form a hydroxyapatite surface layer that chemically bonds to bone and dentin, enabling true tissue integration.
AGD Dental Materials and Biomaterials 5
Which resin monomer is most commonly used as the base in contemporary dental adhesive systems due to its bifunctional nature?