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 role of surface conditioning (sandblasting with alumina) on metal surfaces before bonding?
Answer: Create surface roughness and remove oxide layer, increasing surface area and enabling micromechanical retention for resin cements
Alumina sandblasting (50 µm particles, 2–3 bar) removes surface oxides and creates micro-roughness, significantly increasing surface area for micromechanical bonding of resin cements to metal frameworks.
What determines the 'gel strength' of alginate impression material?
Answer: Cross-link density of the alginate gel — controlled by the ratio of alginate to calcium sulphate (accelerator)
Gel strength depends on the number of calcium-alginate cross-links; too few (under-filled) create a weak gel that tears, while optimal cross-linking provides sufficient tear strength for impression removal.
What is 'galvanism' in the context of metallic dental restorations?
Answer: Generation of electric currents between dissimilar metals in an electrolyte (saliva) — can cause pain and accelerated corrosion
Galvanic currents arise when two dissimilar metals (e.g., amalgam adjacent to a gold crown) are in contact via saliva electrolyte; the current can cause pain and accelerates corrosion of the less noble metal.
What is the most important property of a luting cement for cementing a posterior zirconia crown?
Answer: Adequate film thickness (≤25 µm) and sufficient compressive strength to withstand masticatory forces
Film thickness must be ≤25 µm to allow complete seating of the crown without hydraulic resistance; compressive strength must resist masticatory forces; resin cements additionally require surface conditioning of zirconia.
Which type of stress results in the fracture of a brittle ceramic restoration under masticatory load?
Answer: Tensile stress at the cementation surface or restoration margins
Although ceramics are loaded in compression occlusally, the tensile stress generated at the cementation surface (from flexure) or at margin defects initiates brittle fracture — ceramics fail in tension.
What is the clinical significance of 'stress corrosion' in ceramic restorations?
Answer: Slow crack growth in ceramic under sustained tensile stress in the presence of moisture, leading to delayed fracture
Stress corrosion (static fatigue) occurs when water molecules react with Si-O-Si bonds at crack tips under tensile stress, slowly propagating the crack — causing delayed fracture of ceramic restorations over time.