Lecture 14: Metal ceramics

What is an abrasive?

a) A material that promotes adhesion between surfaces

b) A product with a hard phase for cutting edges

c) A tool used for thermal insulation

d) A material primarily used for polishing metals

b) A product with a hard phase for cutting edges

Which of the following is NOT a thermal property of metals?

a) Expansion

b) Melting

c) Shrinkage

d) Adhesion

d) Adhesion

What is the function of stronger bonding in abrasives?

a) To enhance flexibility of the abrasive

b) To work on soft materials

c) To work on hard materials

d) To reduce particle size

c) To work on hard materials

What do the first three numbers in the ISO standard for abrasive instruments represent?

a) Material

b) Type of attachment

c) Shape and size

d) Largest diameter of the working head

a) Material

What are the natural origin pastes and powders used in polishing?

a) Fe₂O₃ and Cr₂O₃

b) Amphorous SiO₂, Pumice, and Chalk

c) Sandpaper and textile brushes

d) White light interferometer

b) Amphorous SiO₂, Pumice, and Chalk

What does the unit Ra represent in surface roughness measurement?

a) Maximum average height of the profile

b) Vertical distance from peak to valley

c) Average surface roughness

d) Arithmetical mean height

c) Average surface roughness

Which of the following is a contact method for measuring surface roughness?

a) White light interferometer

b) Laser microscope

c) Atomic force microscope

d) Black brush

c) Atomic force microscope

What factors affect abrasion rates?

a) Speed and pressure

b) Lubricants and particle size

c) Both a and b

d) None of the above

c) Both a and b

Whydoresin composite restorations present a unique polishing problem?

a) Due to their uniform composition

b) Because they contain soft resin and hard filler

c) Because they are resistant to polishing

d) Due to their high melting point

b) Because they contain soft resin and hard filler

What is the importance of surface roughness in dentistry?

a) Reducing bacterial adhesion

b) Enhancing oral cell interaction

c) Improving surface finish

d) All of the above

d) All of the above

What are the technological properties of metals?

a) Viscosity, Imbibition, Solubility

b) Expansion, Shrinkage, Boiling

c) Adhesion, Sorption, Wetting

d) Plasticity, Forging, Hammering

d) Plasticity, Forging, Hammering

What are the accessory materials used as pastes and powders?

a) Felt, Sandpaper, Black brush, White brush

b) Pumice, Chalk, Amphorous SiO₂

c) Fe₂O₃ and Cr₂O₃

d) Stylus and Laser Microscope

a) Felt, Sandpaper, Black brush, White brush

What type of abrasive produces deeper scratches?

a) Rounder particles

b) Sharp particles

c) Larger particles

d) Smaller particles

b) Sharp particles

How does increased applied force affect abrasion?

a) Produces shallower scratches

b) Reduces material removal rate

c) Produces deeper and wider scratches

d) Has no significant effect

c) Produces deeper and wider scratches

How are polishing pastes classified?

a) By size of particle and aggregate state

b) By solvent used

c) By material origin

d) Both a and b

d) Both a and b

What is the purpose of using lubricants during abrasion?

a) To increase friction

b) To reduce heat and enhance material removal

c) To prevent abrasive particle wear

d) To increase the hardness of the substrate

b) To reduce heat and enhance material removal

What are the non-contact methods for measuring surface roughness?

a) Stylus and atomic force microscope

b) Laser microscope and white light interferometer

c) Sandpaper and felt

d) Brushes from textile or leather

b) Laser microscope and white light interferometer

Which metal oxide paste is used for polishing gold?

a) Cr₂O₃

b) Fe₂O₃

c) Amphorous SiO₂

d) Pumice

b) Fe₂O₃

What does the unit Rz indicate in surface roughness?

a) Maximum average height of the profile

b) Vertical distance from peak to the lowest valley

c) Average surface roughness

d) Arithmetical mean height

a) Maximum average height of the profile

What method removes material using air-pressure–propelled abrasive particles?

a) Air-particle abrasion

b) Bonded abrasion

c) Relief polishing

d) Resin wear

a) Air-particle abrasion

What is the role of wetting in metal properties?

a) Enhances electrical conductivity

b) Increases particle size during abrasion

c) Reduces thermal expansion

d) Promotes better adhesion between surfaces

d) Promotes better adhesion between surfaces

Which method involves comparing surface roughness by visual or tactile means?

a) Non-contact methods

b) Contact methods

c) Comparative methods

d) Bonded abrasion

c) Comparative methods

What is the primary reason for relief polishing issues in resin composites?

a) Unequal wear rates of resin and filler

b) High thermal expansion rates

c) Low hardness compared to other materials

d) Incompatibility with lubricants

a) Unequal wear rates of resin and filler

Which abrasive material is commonly used for all types of dentures?

a) Pumice

b) Cr₂O₃

c) Chalk

d) Amphorous SiO₂

b) Cr₂O₃

What are the physical properties of metals listed in the text?

a) Plasticity, forging, and rolling

b) Viscosity, adhesion, and thermal conductivity

c) Melting, boiling, and shrinkage

d) Sorption, shrinkage, and particle size

b) Viscosity, adhesion, and thermal conductivity

What is the function of bonded abrasives?

a) To ensure abrasive particles are held tightly together

b) To remove material using air propulsion

c) To polish only soft materials

d) To classify particle size

a) To ensure abrasive particles are held tightly together

What do numbers 7-10 in the ISO standard for abrasive instruments represent?

a) Largest diameter of the working head

b) Type of attachment

c) Material of the abrasive

d) Shape and size of the abrasive

d) Shape and size of the abrasive

What material is used as a hard brush accessory?

a) Black brush

b) Felt

c) Leather

d) Sandpaper

a) Black brush

What does Rmax measure in surface roughness?

a) Arithmetical mean height

b) Vertical distance from peak to the lowest valley

c) Maximum average height of the profile

d) Average surface roughness

b) Vertical distance from peak to the lowest valley

Which property is directly affected by large differences in hardness between the abrasive and substrate?

a) Particle size

b) Abrasion rate

c) Thermal conductivity

d) Electroconductivity

b) Abrasion rate

What is the key factor that determines the depth of scratches during abrasion?

a) Speed of the process

b) Particle shape and size

c) Lubricants used

d) Substrate adhesion

b) Particle shape and size

What are the solvent options for polishing pastes?

a) Water and petroleum products

b) Amphorous SiO₂ and Pumice

c) Felt and sandpaper

d) Fe₂O₃ and Cr₂O₃

a) Water and petroleum products

Which abrasive material originates from natural sources?

a) Fe₂O₃

b) Amphorous SiO₂

c) Cr₂O₃

d) Laser microscope

b) Amphorous SiO₂

34. Which property allows metals to be processed through grinding and polishing?

a) Surface tension

b) Electroconductivity

c) Plasticity

d) Imbibition

c) Plasticity

What does the last three digits of the ISO standard for abrasive instruments

indicate?

a) Shape and size of the abrasive

b) Largest diameter of the working head in 1/10 mm

c) Material of the abrasive

d) Type of attachment

b) Largest diameter of the working head in 1/10 mm

Which abrasive accessory is suitable for softer applications?

a) Black brush

b) White brush

c) Felt

d) Sandpape

b) White brush

Which is NOT a factor affecting abrasion rates?

a) Particle shape

b) Speed of the process

c) Resin wear

d) Lubricants

c) Resin wear

Which property measures the arithmetical mean height of surface roughness?

a) Sa

b) Rz

c) Ra

d) Rmax

a) Sa

What type of microscope is used in non-contact methods for surface roughness measurement?

a) Atomic force microscope

b) Stylus microscope

c) White light interferometer

d) Black brush

c) White light interferometer

What material is used for polishing gold in dentistry?

a) Fe₂O₃

b) Amphorous SiO₂

c) Cr₂O₃

d) Pumice

a) Fe₂O₃

What is the primary factor that influences surface roughness in restorative materials?

a) Thermal properties

b) Particle size and shape

c) Electrical conductivity

d) Melting point

b) Particle size and shape

What type of abrasives require strong bonding?

a) Natural abrasives

b) Abrasives for soft materials

c) Abrasives for hard materials

d) Synthetic abrasives

c) Abrasives for hard materials

What classification of polishing pastes is based on particle size?

a) Hard, semi-hard, and paste-like

b) Water-based and petroleum-based

c) Harsh, medium, and fine

d) Rough and smooth

c) Harsh, medium, and fine

Which process is NOT considered a technological property of metals?

a) Forging

b) Melting

c) Rolling

d) Milling

b) Melting

What is the typical result of abrasion with rounder particles under equal force?

a) Deeper abrasion

b) Shallower scratches

c) Faster material removal

d) Uneven surface finish

b) Shallower scratches

Which method of measuring surface roughness involves a laser microscope?

a) Contact methods

b) Non-contact methods

c) Stylus-based methods

d) Comparative methods

b) Non-contact methods

What polishing material is used for resin composite restorations to prevent uneven wear?

a) Cr₂O₃

b) Amphorous SiO₂

c) Fe₂O₃

d) Specialized soft abrasives

d) Specialized soft abrasives

What does the ISO standard's second set of three numbers represent for abrasives?

a) Type of attachment

b) Material of abrasive

c) Largest diameter of the working head

d) Shape and size

a) Type of attachment

Which surface roughness unit measures the vertical distance between the highest peak and lowest valley?

a) Rz

b) Rmax

c) Sa

d) Ra

b) Rmax

Why is bacterial adhesion an important consideration in surface roughness?

a) It enhances material longevity

b) It increases resistance to polishing

c) It impacts oral health and hygiene

d) It reduces thermal conductivity

c) It impacts oral health and hygiene

Which abrasive material is primarily used for polishing dentures?

a) Fe₂O₃

b) Cr₂O₃

c) Pumice

d) Chalk

b) Cr₂O₃

How does speed affect the abrasion rate?

a) Increases with higher speed

b) Increases with decreased speed

c) Speed has no impact

d) Slows down abrasion with higher speed

a) Increases with higher speed

Which material is classified as a natural-origin abrasive?

a) Sandpaper

b) Amphorous SiO₂

c) Black brush

d) Leather

b) Amphorous SiO₂

What defines surface finish in dental materials?

a) Hardness and elasticity

b) Resistance to bacterial adhesion

c) Average abrasion depth

d) Quality of the final polished surface

d) Quality of the final polished surface

What aspect of abrasives determines their ability to remove material efficiently?

a) Color of the abrasive

b) Type of solvent used

c) Difference in hardness between abrasive and substrate

d) Lubricant compatibility

c) Difference in hardness between abrasive and substrate