ADEX Dental Biomaterials 5 — Questions and Answers
Question 1: What does the term 'wettability' mean in the context of dental adhesive materials?
- The material's resistance to dissolution in oral fluids
- The ability of a liquid material to spread over and contact a surface (Correct answer)
- The water absorption capacity of a cured resin
- The hydrophilicity of dentin bonding agents in wet conditions
Correct answer: The ability of a liquid material to spread over and contact a surface
Wettability describes how well a liquid spreads across a surface; materials with low contact angles spread readily, promoting intimate contact and adhesion.
Question 2: Amalgam creep refers to:
- Corrosion of amalgam margins over time in the oral environment
- Slow plastic deformation of amalgam under sustained compressive load (Correct answer)
- Setting expansion of amalgam beyond acceptable limits
- Fracture of the amalgam isthmus under occlusal stress
Correct answer: Slow plastic deformation of amalgam under sustained compressive load
Creep in amalgam is time-dependent plastic deformation that occurs under sustained compressive stress, which can lead to overhanging margins and marginal breakdown.
Question 3: Which component of a dentin bonding system is responsible for penetrating and sealing the dentinal tubules?
- Etchant (phosphoric acid)
- Primer (Correct answer)
- Adhesive resin
- Bond activator
Correct answer: Primer
The primer contains hydrophilic monomers that penetrate the demineralized collagen network and dentinal tubules to create a hybrid layer and resin tags.
Question 4: A dental material is described as having high 'resilience.' This means the material:
- Fractures easily under low stress
- Can absorb elastic strain energy without permanent deformation (Correct answer)
- Has a high coefficient of thermal expansion
- Returns to its original shape only after plastic deformation
Correct answer: Can absorb elastic strain energy without permanent deformation
Resilience is the ability of a material to absorb energy elastically (within the proportional limit) and return to its original shape upon removal of the load.
Question 5: Which characteristic of gypsum products determines their final strength: dental plaster (Type II) vs. die stone (Type IV)?
- Type IV uses alpha-hemihydrate with lower water-to-powder ratio, producing denser crystals (Correct answer)
- Type II contains additives that accelerate setting to create a stronger matrix
- Type IV is produced by calcination under vacuum rather than steam
- Type II has smaller particle size allowing tighter packing of crystals
Correct answer: Type IV uses alpha-hemihydrate with lower water-to-powder ratio, producing denser crystals
Die stone (Type IV) uses alpha-hemihydrate crystals that are denser and more regular in shape, requiring less water per gram and producing a denser, stronger set material than plaster's beta-hemihydrate.
Question 6: When a patient bites through a celluloid crown form filled with composite, the purpose of making small vent holes is to:
- Allow oxygen to initiate polymerization at the surface
- Release excess material and prevent air entrapment (Correct answer)
- Permit moisture from saliva to activate the self-cure mechanism
- Enable the clinician to assess the depth of material placement
Correct answer: Release excess material and prevent air entrapment
Vent holes in crown forms allow air bubbles and excess composite to escape as the patient bites down, reducing voids in the final restoration.
Question 7: What is the role of an oxygen inhibition layer on the surface of a light-cured composite restoration?
- It protects the restoration from staining during the first 24 hours
- It is an incompletely polymerized tacky surface layer that can bond subsequent increments or veneers (Correct answer)
- It prevents post-cure shrinkage from occurring at the surface
- It acts as a lubricant to aid polishing procedures immediately after cure
Correct answer: It is an incompletely polymerized tacky surface layer that can bond subsequent increments or veneers
Oxygen inhibits polymerization at the composite surface, leaving a thin uncured layer that is advantageous for bonding additional increments or veneers chemically.
ADEX Dental Biomaterials 5
What does the term 'wettability' mean in the context of dental adhesive materials?