Dental Materials: Ceramic Systems Overview

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Questions and Answers

What was one of the first hot-isostatically pressed core ceramics introduced in dentistry?

IPS Empress (correct)

Vitadur N

Dicor

Cerestore

Which feature contributes to the increased strength and toughness of glass-ceramics?

Increased flexural strength

Addition of metal particles

Partial devitrification through heat treatment (correct)

Presence of glassy structure

Which ceramic material is specifically limited to anterior single-unit restorations due to its properties?

Vitadur N

Cerestore

Dicor

IPS Empress (correct)

What innovative process did MacCulloch propose for fabricating crowns?

Continuous glass-molding Signup and view all the answers

Which of the following materials is derived from a quaternary ceramic system?

Dicor Signup and view all the answers

What manufacturing process was used to produce the first commercially available castable ceramic material for dental use?

Lost wax casting Signup and view all the answers

Which material is known for having been limited to single-unit restorations but achieved reasonable success rates?

All of the above Signup and view all the answers

What is the main purpose of incorporating crystalline particles during the heat treatment of glass-ceramics?

To prevent crack propagation Signup and view all the answers

What process is referred to as ceramming in glass-ceramics?

Nucleation and growth of microscopic crystals Signup and view all the answers

Which property of Dicor MGC significantly decreases after the tensile surface is ground?

Flexure strength Signup and view all the answers

What is the typical flexure strength of leucite-based glass-ceramics?

112 MPa Signup and view all the answers

What component is commonly found in the glass-ceramics mentioned in the content?

Lithia disilicate Signup and view all the answers

Why are leucite-based glass-ceramics not recommended for molar crowns?

They have low flexure strength and fracture toughness Signup and view all the answers

What is a characteristic of lithia disilicate glass-ceramics regarding their processing?

They have a narrow sintering range. Signup and view all the answers

What is a potential issue with veneered prostheses made from core ceramics?

They may chip or crack. Signup and view all the answers

Why are conventional feldspathic porcelain veneers not compatible with lithia disilicate core frameworks?

They have a higher thermal expansion coefficient. Signup and view all the answers

Which of the following materials is known to have improved strength due to the inclusion of ZrO2?

Lithia disilicate glass-ceramics Signup and view all the answers

What is the main controlling mechanism believed to be involved in the degradation process of ceramics?

Presence of OH– groups breaking atomic bonds Signup and view all the answers

Which glass-infiltrated core ceramic system is indicated primarily for crown copings and frameworks?

In-Ceram Zirconia Signup and view all the answers

What is the primary reason for doping zirconia with metallic oxides?

To stabilize the tetragonal phase and prevent microcrack formation Signup and view all the answers

Which of the following best describes fully stabilized zirconia (FSZ)?

It is formed when more than 8 mol% yttria is added to zirconia. Signup and view all the answers

What is the typical mean flexure strength of In-Ceram Spinel ceramic?

350 MPa Signup and view all the answers

What is the consequence of the transformation from tetragonal to monoclinic zirconia?

It leads to microcrack development and reduced strength. Signup and view all the answers

Which material primarily consists of 62 wt% alumina and 20 wt% zirconia?

In-Ceram Zirconia Signup and view all the answers

Which oxide is most commonly used as a stabilizer for dental zirconia applications?

Yttria (Y2O3) Signup and view all the answers

What process is used to ensure sufficient resin bonding to the Procera AllCeram core ceramic?

Sandblasting with silica-coated alumina particles Signup and view all the answers

What structural element is critical for the fracture toughness of tetragonal zirconia polycrystals (TZP)?

Metastable tetragonal crystallites below a critical size Signup and view all the answers

In which temperature range does zirconia undergo transformation from the tetragonal phase to the cubic phase?

Between 1167 and 2367 °C Signup and view all the answers

What phenomenon occurs when sufficient tensile stress is applied to a crack in zirconia?

The tetragonal crystals transform to the stable monoclinic phase. Signup and view all the answers

Which property of zirconia is improved with high tetragonal phase content?

Fracture toughness Signup and view all the answers

What type of zirconia contains nanosized metastable tetragonal particles precipitated in a cubic phase matrix?

Partially stabilized zirconia (PSZ) Signup and view all the answers

The transition from monoclinic to tetragonal zirconia usually results in what percentage of volume increase?

3% to 5% Signup and view all the answers

What is transformation toughening responsible for in yttria-stabilized zirconia ceramics?

Enhancing fracture resistance and survival probabilities Signup and view all the answers

What phase transformation occurs due to excessive grinding of zirconia?

Tetragonal to monoclinic Signup and view all the answers

Which of the following is true regarding the thermal treatment of Y-TZP after grinding?

It promotes the conversion of monoclinic to tetragonal phase Signup and view all the answers

What is a disadvantage of using all-zirconia crowns?

They can cause excessive enamel wear Signup and view all the answers

Increased yttria content in zirconia leads to which effect?

Greater translucency Signup and view all the answers

What is the relationship between grain size and fracture toughness in zirconia?

Fracture toughness increases with larger grain sizes Signup and view all the answers

What effect does hydrothermal degradation have on Y-TZP zirconia?

It compromises long-term performance Signup and view all the answers

Which type of milling is least likely to affect the flexural strength of coarse-grained zirconia?

Grinding with fine-grit burs Signup and view all the answers

What is one of the main challenges with monolithic zirconia crowns?

They are difficult to adjust for occlusion Signup and view all the answers

What is a primary concern with very large grain sizes in zirconia?

Premature transformation leading to microcracking Signup and view all the answers

Study Notes

Ceramic-Ceramic or All-Ceramic Systems

The use of ceramic crowns and bridges has increased over the past 20 years
A glass- ceramic material is shaped as glass, then heated causing it to partially crystallize.
The first glass-ceramic for dental use was Dicor
Dicor was created by Corning Glass Works and marketed by Dentsply International.
The flexure strength of Dicor’s machinable glass-ceramic (MGC) decreased after grinding.
The glass-ceramic is heated, a process called ceramming, to grow microscopic plate-like crystals in the glass.
Dicor glass ceramic produced good aesthetics through a chameleon effect.
Newer glass-ceramics are based on leucite, lithia disilicate, and hydroxyapatite.
Leucite-based glass-ceramics are used for anterior veneers and crowns and premolar inlays, onlays, and crowns.
Lithia disilicate materials have a narrow sintering range, which requires specialized processing.
Lithia disilicate-based glass-ceramics have a higher flexural strength compared to glass-ceramics based on leucite.
Veneered lithia disilicate-based glass-ceramic restorations may be susceptible to chipping.

Hot-Isostatically Pressed Glass-Ceramics

Hot-pressed leucite-based glass-ceramics have been used for many years.
The most widely used leucite-based products are IPS Empress, Cerpress SL, Finesse, and IPS e.max CAD.
Leucite-based glass-ceramics have lower flexural strength and fracture toughness.
Lithia disilicate glass-ceramics have higher flexural strength and fracture toughness.

Fluorapatite Glass-Ceramic

Nano-fluorapatite glass-ceramic veneer is compatible with lithia disilicate glass-ceramic core material.

Zirconia-Based Ceramics

Zirconia is a white crystalline oxide of zirconium with a low thermal conductivity.
Zirconia is chemically inert and highly corrosion resistant.
In dentistry, zirconia is used for crown and bridge applications.
Pure zirconia powder has a monoclinic crystal structure at room temperature.
The transition from tetragonal to monoclinic phase results in a volume increase.
Stabilizers, including magnesia, lime, yttria, and ceria, are added to zirconia.

Stabilized Zirconia

If a larger concentration of stabilizer is added, the zirconia becomes fully stabilized zirconia (FSZ).
Partially stabilized zirconia (PSZ) or tetragonal zirconia polycrystal (TZP) contain 3 to 5 mol% of stabilizers.
Magnesia produces Mg-PSZ.
Ceria is used in Ce-TZP/Al2O3 core ceramic.
The fracture toughness of tetragonal 3Y-TZP is higher than nondoped monoclinic zirconia.

Transformation Toughening

When sufficient stress develops in the structure, the metastable tetragonal crystals transform to the monoclinic form.
This transformation toughening increases flexural and tensile fracture resistance.
Regeneration heat treatment of machined or superficially ground Y-TZP converts the monoclinic phase back to the tetragonal phase.

Monolithic Zirconia

Monolithic zirconia is used to reduce the fracture susceptibility of ceramic restorations.
All-zirconia crowns have high fracture resistance but may cause undue wear of opposing enamel.
Monolithic zirconia is not translucent.
Manufacturers have increased the yttria content to increase translucency.
Translucent zirconia ceramics have lower strength and fracture toughness compared to non-translucent zirconia.

Fracture Strength of Zirconia

The fracture toughness of zirconia tends to increase with increasing grain size.
For 3Y-TZP, fracture strength increases linearly with grain size until reaching a critical grain size.
Grinding can affect the flexural strength of zirconia based on grain size.

Hydrothermal Degradation

Y-TZP is susceptible to hydrothermal degradation.
Longer exposure times at oral temperatures may degrade zirconia.

Degradation Process

The degradation process starts with the transformation of the surface to the monoclinic phase.
This transformation spreads to adjacent grains due to stresses developed during the process.
OH– groups are believed to be responsible for breaking the atomic bonds at the surface, leading to residual stresses and the initial transformation from the tetragonal to monoclinic phase.

Glass-Infiltrated Core Ceramics

Three glass-infiltrated core ceramic systems have been developed to minimize sintering shrinkage and ensure the fit of ceramic prostheses.
The systems are based on partially sintered alumina, magnesia-alumina spinel (MgAl2O4), and zirconia-alumina core.
Each system can be infiltrated with a lanthanum glass without significant dimensional change.

VITA In-Ceram Alumina

Contains approximately 85 vol% alumina.
Formed by a slip-casting process, producing dense particle packing against a porous die.
A partially sintered structure is formed after firing at 1120 °C for 10 hours or more.
The porous core ceramic framework is then infused with molten lanthanum glass.

In-Ceram Spinel (ICS)

A magnesia alumina spinel (MgAl2O4) core ceramic.
More translucent than In-Ceram Alumina or In-Ceram Zirconia.
Has a significantly lower mean strength (∼350 MPa vs.∼600 MPa).

In-Ceram Zirconia

A zirconia-toughened alumina (ZTA) material.
Composed of 62 wt% alumina, 20 wt% zirconia, and ∼18 wt% infiltrated glass.
Indicated for crown copings and three-unit anterior and posterior frameworks.
No shrinkage associated with the glass infiltration process, ensuring marginal adaptation comparable to the hot-pressing method.
Subject to transformation toughening with conversion from tetragonal to monoclinic phases in areas of stress.
Strength is doubled, toughness is increased two to four times.

Alumina Core Ceramic

Procera AllCeram (Nobel Biocare) is an alumina-core ceramic indicated for anterior and posterior crowns.
Production involves a die made from an impression and digitized using a mechanical profiling device.
An oversized die is produced onto which pure alumina is dry-pressed.
The oversized green alumina body is sintered, resulting in shrinkage that gives the desired size and shape.
A feldspathic porcelain veneer is applied and sintered.
More translucent than In-Ceram Zirconia and has comparable strength (620–700 MPa).
The surface is sandblasted with silica-coated alumina particles for sufficient resin bonding.

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Description

Explore the evolution and applications of ceramic crowns and bridges in dentistry. This quiz covers key materials such as Dicor, leucite-based, and lithia disilicate glass-ceramics, along with their processing and aesthetic benefits. Test your knowledge on the properties and uses of these innovative dental materials.