Dental Materials Science Flashcards
6 cards from real MJDF practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Dental Materials Science flashcards as text
What is the purpose of using a rubber dam in adhesive dentistry?
Answer: Moisture control — prevents saliva and blood contamination that impair adhesive bond formation
Moisture contamination by saliva, crevicular fluid, or blood prevents adequate enamel/dentine conditioning and adhesive penetration, dramatically reducing bond strength; rubber dam isolation is the gold standard for adhesive procedures.
What is the ISO definition of 'biocompatibility' for a dental material?
Answer: The ability of a material to perform with an appropriate host response in a specific application — not causing adverse biological reactions
Biocompatibility means the material must be well tolerated by the host tissues in its specific clinical application, not eliciting pulpal, mucosal, systemic, or genotoxic adverse effects.
What is the main disadvantage of zinc oxide eugenol as a temporary cement?
Answer: Eugenol inhibits polymerisation of resin composites — cannot be used under composite restorations
Residual eugenol from ZOE cements inhibits free-radical polymerisation of composite resins; if ZOE is used as a temporary restoration or liner, eugenol contamination prevents composite bonding and curing.
What property makes cobalt-chromium alloy preferred over gold alloy for removable partial denture frameworks?
Answer: Higher stiffness (modulus of elasticity) and lower density at lower cost — thinner, lighter frameworks possible
Co-Cr alloys have a high modulus of elasticity (allowing thinner, stiffer clasps that do not permanently deform) and lower density than gold (lighter dentures), at a much lower cost, despite more challenging fabrication.
What does 'work hardening' (strain hardening) mean in dental alloys?
Answer: Strengthening of metal through plastic deformation, which increases dislocation density and resists further deformation
Work hardening occurs when metal is plastically deformed (e.g., clasp adjustment); dislocations accumulate, impeding further dislocation movement and increasing hardness and yield strength — but also reducing ductility.
What is the main clinical problem caused by water sorption in PMMA denture bases?
Answer: Dimensional change (slight expansion), reduced strength, and potential release of residual monomer into saliva
PMMA absorbs water (approximately 0.5–0.69 mg/cm²), causing slight expansion (partly compensating for polymerisation shrinkage), plasticisation reducing strength, and potentially releasing residual methyl methacrylate monomer.