CDT Dental Materials Science 2 — Questions and Answers
Question 1: Which type of gypsum product has the highest compressive strength and is used for die fabrication?
- Plaster of Paris
- Dental stone
- Die stone (Type IV) (Correct answer)
- Orthodontic plaster
Correct answer: Die stone (Type IV)
Type IV die stone has the highest compressive strength among gypsum products, making it ideal for accurate die fabrication.
Question 2: What is the primary advantage of using addition-cured silicone (VPS) impression materials over condensation silicones?
- Lower cost
- Dimensional stability with minimal shrinkage (Correct answer)
- Faster setting time
- Better hydrophilicity in wet fields
Correct answer: Dimensional stability with minimal shrinkage
Addition-cured silicones (VPS) produce no by-products during polymerization, resulting in excellent dimensional stability and minimal shrinkage.
Question 3: The elastic modulus (stiffness) of a restorative material is most relevant when evaluating:
- Color stability under UV light
- Resistance to deformation under occlusal load (Correct answer)
- Thermal conductivity to the pulp
- Susceptibility to galvanic corrosion
Correct answer: Resistance to deformation under occlusal load
Elastic modulus describes a material's stiffness and its ability to resist deformation under applied occlusal forces.
Question 4: Which base metal alloy component is primarily responsible for the natural oxide layer that improves ceramic bonding in PFM restorations?
- Molybdenum
- Tungsten
- Beryllium or tin (Correct answer)
- Platinum
Correct answer: Beryllium or tin
Beryllium and tin in base metal alloys form surface oxides during oxidation that chemically bond to porcelain for improved ceramic adhesion.
Question 5: A dental wax pattern that exhibits 'flow' at mouth temperature would most likely cause:
- Improved marginal adaptation
- Distortion of the final casting (Correct answer)
- Better surface detail reproduction
- Enhanced investment setting
Correct answer: Distortion of the final casting
Excessive wax flow at oral temperature causes pattern distortion before investing, leading to an inaccurate final casting.
Question 6: The phenomenon where porcelain and metal expand and contract at different rates during firing and cooling is quantified by:
- Vickers hardness number
- Coefficient of thermal expansion (CTE) (Correct answer)
- Knoop hardness value
- Proportional limit
Correct answer: Coefficient of thermal expansion (CTE)
The coefficient of thermal expansion (CTE) must be closely matched between porcelain and metal to prevent cracking or delamination.
Question 7: In casting alloy selection, which property best indicates a material's ability to be shaped into thin margins without cracking?
- Hardness
- Ductility (Correct answer)
- Compressive strength
- Thermal conductivity
Correct answer: Ductility
Ductility is the ability of a metal to be deformed plastically without fracturing, essential for burnishing thin casting margins.
CDT Dental Materials Science 2
Which type of gypsum product has the highest compressive strength and is used for die fabrication?