Dental Ceramics Properties

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Questions and Answers

What is the primary composition of ceramics at the atomic level?

Metallic oxide

Organic metal

Inorganic nonmetal glass phase with crystalline fillers (correct)

Carbon-based polymer

What happens when the glassy phase increases in ceramics?

The mechanical properties improve

The translucency increases, but the material becomes weaker (correct)

The surface hardness decreases

The thermal insulation decreases

What is one of the advantages of ceramics in dentistry?

Good resistance to shear stresses

Low biocompatibility

High thermal conductivity

Excellent esthetics (correct)

What is a limitation of ceramics in dentistry?

Brittle and very poor under tensile and shear stresses Signup and view all the answers

How can dental ceramics be classified?

By microstructure, processing method, fusing temperature, translucency, and fracture resistance Signup and view all the answers

What are the two directions of development observed in dental ceramics?

Developing new high-strength ceramics and developing new dental ceramics classification Signup and view all the answers

What are examples of high-strength ceramics?

Lithium disilicate and zirconia-reinforced lithium silicate Signup and view all the answers

What is a characteristic of the thermal properties of ceramics?

Thermal expansion coefficient close to natural tooth structure Signup and view all the answers

What is the average size of lithium meta-silicate crystals in ZLS ceramics?

0.5–0.7 µm Signup and view all the answers

What is the percentage of zirconium oxide in the glassy matrix of ZLS ceramics?

10% Signup and view all the answers

What is a characteristic of zirconia lithium crystals?

Fine grained Signup and view all the answers

What happens to the strength of Celtra Duo blocks after milling?

It decreases from 420 MPa to 200 MPa Signup and view all the answers

What is the flexural strength of high leucite containing glass?

160-170 MPa Signup and view all the answers

What is the effect of polishing on the strength of Celtra Duo blocks?

It increases the strength to 210 MPa Signup and view all the answers

What is the main advantage of lithium disilicate based restorations?

High flexural strength due to the shape and volume of crystals Signup and view all the answers

What is the effect of glaze firing on the strength of Celtra Duo blocks?

It increases the strength to 370 MPa Signup and view all the answers

What is the minimum thickness required for veneers in lithium disilicate restorations?

0.4mm Signup and view all the answers

What is the composition of fluorapatite based ceramics?

19–23% fluorapatite Signup and view all the answers

Which of the following is NOT an indication for high leucite containing glass restorations?

Posterior crowns Signup and view all the answers

What is the flexural strength of fluorapatite based ceramics?

110 MPa Signup and view all the answers

What is the processing method used for IPS Empress CAD blocks?

CAD/CAM Signup and view all the answers

What is the derivative of lithium disilicate with smaller crystallites?

Zirconia Lithium Silicate (ZLS) Signup and view all the answers

What is the maximum number of units that can be fabricated using lithium disilicate restorations?

3 units Signup and view all the answers

What is the main characteristic of lithium disilicate crystals that allows for high translucency?

Low refractive index Signup and view all the answers

What is the ideal coefficient of thermal contraction of the veneering porcelain compared to the ceramic coping?

Slightly lower Signup and view all the answers

What is the primary purpose of minimizing the number of firing cycles?

To prevent the formation of defects in the porcelain Signup and view all the answers

What is the effect of leucite on the thermal contraction coefficient of the porcelain?

It increases the coefficient of thermal contraction Signup and view all the answers

What is the mechanism of toughening that occurs at the tip of the crack during the development of tensile stress in yttria-stabilized zirconia?

Transformation toughening Signup and view all the answers

What is the composition of dental porcelain?

Glassy alumino-silicate glass matrix with crystalline phase embedded Signup and view all the answers

What is the type of ceramic that feldspathic porcelain is classified as?

Predominantly glass ceramic Signup and view all the answers

What is the typical range of flexural strength of feldspathic porcelain?

70-90 MPa Signup and view all the answers

What is an example of a monolithic restoration that uses feldspathic porcelain?

Ceramic crown Signup and view all the answers

What is the main advantage of 95-98% zirconia crystals?

High strength and fracture toughness Signup and view all the answers

What is the main difference between 3Y-TZP and 2nd generation zirconia?

Grain size and sintering temperature Signup and view all the answers

What is the main advantage of monolithic zirconia?

No need for veneering Signup and view all the answers

What is the percentage of yttria in 3Y-TZP?

3 mole% Signup and view all the answers

What is the main mechanism of transformation toughness?

Absorption of stress energy Signup and view all the answers

What is the main indication of 3Y-TZP?

All of the above Signup and view all the answers

What is the main drawback of 3Y-TZP?

Chipping of veneering porcelain Signup and view all the answers

What is the flexural strength of 4th generation zirconia?

500 to 800 Mpa Signup and view all the answers

Study Notes

Atomic Composition of Ceramics

Ceramics are composed of inorganic nonmetal glass phase with some crystalline fillers like Silica (Si), Zirconia (Zr), and Alumina (Al)
The glassy phase affects translucency, but makes ceramics weaker and more prone to crack propagation
The crystalline phase improves mechanical properties, but alters esthetics

Properties of Ceramics

Biocompatibility
Excellent esthetics
High surface hardness
Thermal insulators with a coefficient of thermal expansion close to natural tooth structure
Mechanical and optical properties vary according to microstructure
Brittle with good resistance to compressive stresses, but poor under tensile and shear stresses, failing by crack propagation

Classification of Dental Ceramics

Classified by microstructure, processing method, fusing temperature, translucency, and fracture resistance
Free-hand layering, casting, pressing, milling, and CAD-CAM are different processing methods

Development of Ceramics

Two approaches: developing high-strength ceramics and minimizing material-related restoration failure
High-strength glass ceramics (lithium disilicate, zirconia-reinforced lithium silicate) and partially stabilized zirconia

Thermal Contraction and Expansion

Coefficient of thermal expansion and contraction should be considered when selecting veneering porcelain
Mismatch between coping and veneering porcelain can leave the porcelain in residual compression, providing additional strength

Chemical Reactions and Thermal Contraction

Chemical reactions occur during porcelain firing temperatures, affecting crystalline leucite concentration and thermal contraction coefficient
Leucite is a high-expansion crystal phase that affects thermal contraction coefficient

Crack Propagation and Toughening

Dispersion strengthening and transformation toughening are methods to interrupt crack propagation
Dispersion strengthening involves adding particles to the ceramic, while transformation toughening uses yttria-stabilized zirconia

Dental Porcelain

Consists of a glassy alumino-silicate glass matrix with crystalline phases (feldspar, quartz, alumina) embedded
Can be classified into feldspathic porcelain, lithium disilicate-based, and zirconia-reinforced lithium silicate ceramics

Feldspathic Porcelain

Glassy matrix with crystalline phases
Indications: monolithic restorations, single full-coverage crowns, inlays, onlays, and veneers
Processing methods: powder and liquid, CAD-CAM, and heat pressing

Lithium Disilicate-Based Ceramics

High translucency and flexural strength (360 MPa)
Indications: thin veneers, inlays, onlays, partial crowns, and minimal invasive crowns
Methods of fabrication: pressable forms and CAD-CAM

Zirconia Lithium Silicate (ZLS) Ceramics

Dual microstructure with lithium meta-silicate and zirconium oxide in solution
Fine-grained, homogeneous structure with high load characteristics and easy milling and polishing
Examples: Vita suprinity, Celtra Duo, and Celtra Press

Fluoroapatite-Based Ceramics

Veneering material only, on zirconia or glass ceramics
Methods of fabrication: free-hand layering and pressing

Polycrystalline Zirconia

Most commonly used, with 95-98% zirconia crystals
Advantages: high flexural strength (1200-1400 MPa) and transformation toughening

Types of Zirconia

3Y-Tetragonal Zirconia Polycrystals (TZP): first generation, used as a core only, with high strength and fracture toughness
2nd Generation: same microstructure as 1st gen, but with changes in grain size, sintering temperature, porosity content, and alumina content
3rd Generation: 4 mole% Y-PSZ, with 25% cubic phase and high translucency
4th Generation: 5 mole% Y-PSZ, with high translucency and flexural strength (500-800 MPa)

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Description

This quiz covers the properties of ceramics used in dentistry, including their composition, translucency, and mechanical properties.