Dental Ceramics and Their Applications

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Questions and Answers

What is a characteristic of glass infiltrated ceramics?

They are typically made with a pure alumina core.

They require higher sintering temperatures than metal ceramic restorations.

They have greater fracture toughness than sintered oxide ceramics.

They often utilize CAD-CAM milling or electrophoresis. (correct)

Which feature makes metal-ceramic bonding effective?

The ceramic must have a higher coefficient of thermal expansion (CTE) than the metal.

The melting temperature of the ceramic must be lower than that of the alloy.

The surface roughness of the metal framework must be minimized.

The ceramic exhibits micro-cracks that limit fracture propagation. (correct)

What is a primary disadvantage of ceramics used in restorations?

They can bond too well with metal, causing brittleness.

They exhibit micro-cracks on the inner surface, reducing durability. (correct)

They have a tendency to create large thermal expansion mismatches.

They cannot be easily shaped or milled.

Which is a requirement for metal-ceramic alloy bonding?

The solidus temperature of the alloy must be less than the sintering temperature. (B) Signup and view all the answers

Which of the following materials are used for sintered oxide ceramics with zirconia cores?

DC-Zirkon and KaVo Everest ZS-Blank (A), 3M Espe LAVA Frame and Procera Zirconia (D) Signup and view all the answers

What is a primary use of ceramics in orthodontics?

Brackets (A) Signup and view all the answers

Which type of ceramic is commonly used for all-ceramic restorations?

Feldspathic ceramics (C) Signup and view all the answers

Which of the following ceramics is used as a core material?

Alumina ceramics (D) Signup and view all the answers

What is the role of hydroxyapatite ceramics in dental procedures?

Filling bone defects (A) Signup and view all the answers

What is the sintering temperature range for low sintering ceramics?

850-1100°C (D) Signup and view all the answers

Which material is included in the ceramic composition for metal-bonded restorations?

Feldspathic ceramics (D) Signup and view all the answers

Which type of ceramic is noted for having good aesthetics but poor mechanical strength?

Silicate ceramics (A) Signup and view all the answers

Which dental application is ceramic implants primarily used for?

Implantology (A) Signup and view all the answers

What distinguishes spinel-reinforced feldspathic ceramics from traditional feldspathic ceramics?

Improved strength (B) Signup and view all the answers

What defines oxide ceramics in terms of composition?

Have a polycrystalline structure (A) Signup and view all the answers

Which type of glass ceramic is specifically known for use in CAD-CAM technology?

Lithium disilicate (B) Signup and view all the answers

Which laboratory processing method involves creating a wax pattern and casting?

Castable (D) Signup and view all the answers

Which CAD-CAM process involves mechanical milling based on optical impressions?

Mechanical milling (A) Signup and view all the answers

What is the main characteristic of glass-infiltrated ceramics?

They are created from a framework of oxide ceramics. (B) Signup and view all the answers

What type of laboratory processing results in precise duplication from a wax-up?

Pressed (A) Signup and view all the answers

What sintering temperature classification includes ceramics fired below 850°C?

Ultra low sintering (C) Signup and view all the answers

What happens when the coefficient of thermal expansion (CTEc) of ceramics is greater than that of metals (CTEm)?

Tensile forces will develop in ceramics, leading to potential cracks. (A) Signup and view all the answers

What is the risk of cracking in ceramics when the coefficient of thermal expansion (CTEc) is less than that of metals (CTEm)?

Reduced significantly due to compressive forces on ceramics. (A) Signup and view all the answers

Which of the following is a significant property of glass-ceramics made of lithium disilicate?

Flexural strength between 350-450 MPa. (C) Signup and view all the answers

What is a characteristic of the adhesive cementation process mentioned?

It increases the strength of the material. (D) Signup and view all the answers

Which statement accurately describes hydroxyapatite glass-ceramics?

They can be developed with a composition of Ca10(PO4)6·2OH. (A) Signup and view all the answers

What effect does the process of ceramization have on glass-ceramics?

It stops the propagation of micro-cracks through the material. (B) Signup and view all the answers

What technological process is mentioned for the production of glass-ceramics?

Casting (D) Signup and view all the answers

Which CTE value range indicates a low risk of internal stresses between ceramics and metals?

CTEc equal to CTEm. (D) Signup and view all the answers

Study Notes

Dental Ceramics Lecture 10

Dental ceramics are classified according to application, fabrication method, and crystalline phase.
All-ceramic restorations are further categorized into subgroups like soft-machined, glass-infiltrated, hard-machined, slip-cast, heat-pressed, and sintered.
Metal-ceramic restorations are a different classification incorporating metal frameworks and veneering materials.
Firing temperature, composition, laboratory processing methods (sintered, castable, pressed, glass-infiltrated, CAD-CAM), and intended use (e.g., prosthetics, orthodontics) are all criteria used for dental ceramic classification.
Firing temperatures are categorized as high (>1300°C), medium (1100-1300°C), low (850-1100°C), and ultra-low (<850°C).
Silicate ceramics are multiphase, with a glassy phase and crystals. They have good aesthetics but poor mechanical strength.
Oxide ceramics are monophase (>90% metallic oxides) and have excellent mechanical strength but poor aesthetics.
Common laboratory processing methods for ceramics include sintering, casting, glass-infiltration, pressing, and CAD-CAM.

Additional Classifications

Sintered: Burning into successive layers onto metallic frameworks, platinum foil, refractory casts, or hydrothermal glass.
Casting: Using wax patterns, molds, and melting ceramic blocks combined with ceramization (thermal crystallization) of the cast framework. A variant involves core casting and veneering.
Glass-infiltration: Creating frameworks from oxide ceramics using CAD-CAM, or by a technician's methods combined with glass-infiltration and veneering.
Pressed: Utilizing wax patterns, molten glass ingots, and pressing into molds with veneering. This often involves precision wax-ups, consistent pre-blended ceramic ingots, and pressing into the ingots.
CAD-CAM: Computer-aided design and manufacturing, using subtractive processes from ceramic ingots. Methods can include mechanical milling (based on optical or copied impressions), sonoerosion, and electrophoresis.

Classification by Usage Domain

Prosthetics: Veneering metallic frameworks or oxide ceramics, single prosthetic restorations (partially or fully ceramic), dental bridges, or implant mesostructures.
Orthodontics: Brackets.
Implantology: Ceramic implants.
Periodontal surgery: Bone defect filling using ceramics based on absorbent hydroxyapatite.
Oro-facial defects therapy: Medication support (e.g., gentamicin) for osteomyelitis treatment.

Ceramics for Metal-Ceramic Restorations

Metal-bonded ceramics (or porcelain-fused-to-metal restorations) are often used for crowns and mixed bridges.
These restorations involve sintering for joining. Variants like traditional feldspathic ceramics are used. Modifications with components like alumina, spinell or leucite enhance properties.

Ceramics for All-Ceramic Restorations

Silicate Ceramics (Feldspathic): Simple restorations (inlays, veneers, crowns, etc.) can be applied on frames, platinum foil, or refractory casts. CAD/CAM methods are also prevalent. Different materials with leucite, sintering, pressing, and CAD/CAM are used (e.g. Vita Blocks, Sirona CEREC Blocks, Mirage, Fortress, Optec-HP, Empress I, Procad, Hi-Ceram.)
Silicate Ceramics (Glass): These utilize leucite, fluormica (castable, pressed, or CAD) with Hydroxyapatite Ceramics (pressed or CAD/CAM) and also involve sintering or castable methods.
Oxide Ceramics: Further divided into glass infiltrated (In-Ceram with alumina or spinell or zirconia), sintered (Procera Alumina, Procera Zirconia, Techceram), or CAD-CAM methods (such as DC-Zirkon, DigiZon HIP, KaVo or Everest ZH-blank, Zirkon).
Yttrium-Stabilized Zirconium Dioxide: High flexural strength, translucent cores, and veneering with compatible ceramics are typical for these. These use CAD-CAM techniques.

Resin-Bonded Ceramics

Feldspathic Ceramics (Sintered/Hot Pressed/CAD-CAM): Typically involve sintering or hot pressing onto dies. CAD-CAM techniques also apply.
Glass Ceramics: Casting into molds of a ceramic in a liquid state, followed by thermal treatments and crystallization (ceramization). This involves Nucleation (crystal formation) and Crystallization (increasing crystal size).

Other Important Considerations

Compatibility: Alloy-ceramic compatibility is crucial. Materials' coefficients of thermal expansion (CTE) need careful matching to avoid internal stresses and cracking. Matching CTE is critical to minimize such issues.
Composition: Feldspathic and leucite composition vary, sometimes to meet different requirements (veneer vs. full ceramic), and different additives can improve these properties.
Methods for Strengthening: Some methods to improve mechanical strength in feldspathic ceramics include using aluminous, magnesium, or synthetic ceramics and adjusting firing temperature and ratios.

History of Dental Ceramics

Early use of feldspathic ceramics and challenges with microcracking led to development of new compositions and processing methods.
Advances included alumina-reinforced feldspathic cores, full ceramic bridges (zirconia core).

Pros/Cons of Dental Ceramics

Pros: Ideal color, biocompatibility, reduced thermal conductivity, good chemical resistance, high compressive strength, and high surface smoothness/gloss.
Cons: Decreased tensile strength, rough surfaces, high price, decreased ability for restorative work, and potential for internal and external cracks and fractures.

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Description

Explore the intricacies of dental ceramics and their various applications in dental restorations and orthodontics. This quiz covers key characteristics, bonding features, and the advantages and disadvantages of different ceramic materials in dentistry.