Free Metals and Alloys MCQs with Answers

• A. All of the above
• B. Hygroscopic expansion
• C. Wax expansion
• D. Thermal expansion

Explanation: Casting alloy contraction is offset by expansion of the wax pattern and investment, including thermal and hygroscopic expansion.

• A. 55
• B. 65
• C. 75
• D. 85

Explanation: Under ADA Specification No. 5, dental gold casting alloys contain at least 75% gold plus platinum-group metals.

• A. Annealing
• B. Degassing
• C. Conditioning
• D. Pickling

Explanation: Pickling uses an acid solution to dissolve surface oxides and other contaminants from a casting after removal from the investment.

• A. NITTINOL wire
• B. Stainless steel wire
• C. TMA wire
• D. Aluminium

Explanation: Nitinol, a nickel-titanium alloy, exhibits shape memory because of reversible austenite-martensite transformation.

• A. Nitric acid
• B. Hydrochloric acid
• C. Sulphuric acid
• D. Phosphoric acid

Explanation: Hydrochloric acid is used as a pickling solution for castings made with gypsum-bonded investment, helping remove adherent investment and…

• A. Iron carbide
• B. Carbon carbide
• C. Chromium carbide
• D. Nickel carbide

Explanation: In stainless steel, chromium carbide formation at grain boundaries can deplete nearby chromium and destroy the protective passive film…

• A. Recovery stage
• B. All of the above
• C. Grain growth stage
• D. Recrystallisation stage

Explanation: Recrystallisation replaces the strained, elongated grains with new strain-free grains, causing a sharp fall in tensile strength and a…

• A. Titanium
• B. Palladium
• C. Platinium
• D. Gold

Explanation: Titanium forms a stable, protective titanium oxide layer that gives excellent corrosion resistance and tissue compatibility in the oral…

• A. Silver fluorides
• B. Silver cyanide
• C. Silver bromide
• D. Silver iodide

Explanation: Silver electroplating commonly uses a silver cyanide electrolyte because cyanide complexes keep silver ions available for controlled…

• A. Attached impurities on undersurface of casting
• B. Inadequate melting temperature
• C. No rapid cooling
• D. Hot spot

Explanation: Suck-back porosity is shrinkage porosity caused by a hot spot, usually at the sprue-casting junction, where solidification is delayed and…

• A. Improper wetting of the wax pattern by the investment
• B. Improper heating of the investment
• C. Improper angulation of sprue
• D. Improper casting pressure

Explanation: Air trapped against a poorly wetted wax pattern produces rounded surface bubbles or nodules in the casting.

• A. Facilitate venting of the mold
• B. Retard the heating of the investment
• C. Permit expansion of the world
• D. All of the above

Explanation: A ring liner provides space for the investment to expand during setting and heating instead of being rigidly confined by the casting ring.

• A. Surface hardness
• B. Strength
• C. Proportion limit
• D. Corrosion resistance

Explanation: Strain hardening generally increases hardness, strength, and proportional limit because plastic deformation raises dislocation density.

• A. Increasing the mould metal temperature difference
• B. Increasing the flow of molten metal
• C. Flaring the point of the sprue attachment
• D. All of the above

Explanation: Flaring the sprue at its attachment provides a larger reservoir of molten alloy and reduces the localized hot spot responsible for…

• A. Nickel
• B. Molybdenum
• C. Chromium
• D. Carbon

Explanation: Carbon is present in stainless steel only in a small amount, yet it strongly affects hardness, strength and corrosion resistance through…

• A. Unreliable spring back
• B. None of the above
• C. Minimal spring back
• D. low spring back

Explanation: Nickel-titanium has pronounced superelasticity and shape-memory behaviour, giving it a high and reliable springback.

• A. Low strength
• B. Low cost
• C. Low weight
• D. Low melting point

Explanation: Titanium has a much lower density than most other base-metal alloys, so appliances made from it can be lighter while retaining useful…

• A. Fibrous
• B. Homogeneous
• C. amorphous
• D. Inhomogenous

Explanation: Cast cobalt-chromium alloys commonly show a dendritic, compositionally segregated microstructure, so the structure is inhomogeneous.

• A. Constitutional supercooling
• B. Constitutional superconductivity
• C. Constitutional supergriting
• D. Constitutional supergraining

Explanation: Dendrites develop when solute rejected at the advancing solidification front lowers the liquidus temperature ahead of it, producing…

• A. Increased ductility
• B. Increased hardness
• C. Better biocompatibility
• D. Increased density

Explanation: Base-metal alloys are generally harder and stronger than noble-metal alloys, although they are usually less ductile and more difficult to…