ADEX Dental Biomaterials 2 — Questions and Answers
Question 1: Which type of dental cement is most biocompatible and commonly used as a base under composite restorations?
- Zinc phosphate cement
- Glass ionomer cement (Correct answer)
- Zinc oxide eugenol cement
- Polycarboxylate cement
Correct answer: Glass ionomer cement
Glass ionomer cement is highly biocompatible, bonds chemically to tooth structure, and releases fluoride, making it ideal as a base under composite restorations.
Question 2: What is the primary setting reaction of zinc phosphate cement?
- Polymerization of resin monomers
- Acid-base reaction between zinc oxide powder and phosphoric acid liquid (Correct answer)
- Chelation between zinc oxide and eugenol
- Ionic crosslinking between polyacrylic acid and calcium
Correct answer: Acid-base reaction between zinc oxide powder and phosphoric acid liquid
Zinc phosphate cement sets via an exothermic acid-base reaction where zinc oxide reacts with phosphoric acid to form zinc phosphate crystals.
Question 3: The term 'work time' in dental materials refers to:
- Time needed to cure the material under a light source
- Total time from mix start until the material is fully set
- Time available for manipulation after mixing before setting begins (Correct answer)
- Time required to polish the restoration after placement
Correct answer: Time available for manipulation after mixing before setting begins
Work time is the period after mixing during which the material can be manipulated and placed before it begins to set.
Question 4: Which property describes a material's ability to withstand repeated loading without fracturing?
- Hardness
- Toughness
- Fatigue resistance (Correct answer)
- Elastic modulus
Correct answer: Fatigue resistance
Fatigue resistance is a material's ability to endure cyclic or repeated stresses over time without failure.
Question 5: Resin-modified glass ionomer (RMGI) differs from conventional glass ionomer primarily because it:
- Contains no fluoride
- Has a dual-cure mechanism including light-activated resin (Correct answer)
- Is exclusively self-adhesive to dentin
- Sets faster due to a chemical accelerator only
Correct answer: Has a dual-cure mechanism including light-activated resin
RMGI incorporates HEMA resin monomers that allow light-curing in addition to the acid-base setting reaction of conventional glass ionomer.
Question 6: What does the term 'coefficient of thermal expansion' mean in the context of dental restorations?
- Rate at which the material dissolves in oral fluids
- Change in material volume per unit temperature change (Correct answer)
- Ability of material to absorb thermal shocks without fracturing
- Temperature at which the material begins to soften
Correct answer: Change in material volume per unit temperature change
The coefficient of thermal expansion measures how much a material expands or contracts per degree of temperature change, and mismatch with tooth structure can cause microleakage.
Question 7: Which bonding mechanism does polycarboxylate cement use to adhere to tooth structure?
- Micromechanical interlocking via acid etching
- Chelation of polyacrylic acid with calcium ions in enamel and dentin (Correct answer)
- Van der Waals forces between resin and collagen
- Ionic bond between phosphate groups and hydroxyapatite
Correct answer: Chelation of polyacrylic acid with calcium ions in enamel and dentin
Polycarboxylate cement forms a true chemical bond through chelation between its polyacrylic acid and calcium ions in the tooth's hydroxyapatite.
ADEX Dental Biomaterials 2
Which type of dental cement is most biocompatible and commonly used as a base under composite restorations?