DENTAL CERAMICS - CQ

Which property best describes the fracture resistance of dental ceramics?

• Fracture toughness best describes the fracture resistance of dental ceramics.

• It measures a material’s ability to resist crack growth under tensile stress, which is critical since ceramics are brittle.

If tensile strength is not a reliable property of dental ceramics, which property is a better measure of the material’s fracture resistance?

• Fracture toughness is a better measure than tensile strength because it reflects a true material property—resistance to crack propagation—

• WHILE tensile strength varies with size, shape, and surface conditions.

What roles do oxygen, potassium, and leucite play in the structure and properties of feldspathic veneering (layering) ceramics?

• Oxygen forms the basic silicate structure

• Potassium acts as a flux that increases thermal expansion

• Leucite crystals further raise the thermal expansion coefficient to match the ceramic with metal frameworks.

Which property of bilayer ceramics is used as a measure of the thermal compatibility of ceramic materials?

• The coefficient of thermal expansion (CTE) is used to measure thermal compatibility.

• Matching the CTE between ceramic layers prevents crack formation due to thermal stress during heating and cooling.

Through what mechanism does transformation toughening increase the fracture resistance of yttria-stabilized zirconia?

• Transformation toughening occurs when stress causes zirconia’s tetragonal crystals to transform into the monoclinic phase

• = Creating compressive forces that stop crack growth and increase fracture resistance.

Which two inventions dramatically increased the success and survival probability of metal-ceramic restorations?

• The development of strong metal-ceramic bonding techniques and the introduction of thermal expansion–matched porcelains greatly improved the durability and success of metal-ceramic restorations.

Which components of ceramics can cause excessive wear of tooth enamel?

• Excessive enamel wear is mainly caused by core ceramics or opaque porcelains that have large or hard crystalline particles and rough, unglazed surfaces.

• The particle type and crystal size make the ceramic surface more abrasive.

• Proper glazing or polishing of veneering ceramics reduces this wear against natural tooth enamel.

How does the leucite content of veneering porcelain for metal-ceramic prostheses control the cracking resistance of the porcelain?

How is the degree of sintering controlled and what parameter defines complete sintering?

• The degree of sintering is controlled by the firing time and temperature used during the heating process.

• Complete sintering is defined when the porcelain reaches its theoretical density (about 95–99% in practice), meaning porosity has been minimized and the particles are fully bonded.

What condition is required of cast metals to achieve ionic and/or covalent bonding to veneering porcelain?

Why should a metal coping or framework have a higher expansion coefficient than its veneering porcelain?