Metal-Ceramic Prostheses Overview

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Questions and Answers

What are the primary components of conventional dental porcelain?

Soda feldspar and calcium carbonate

Silica and potash feldspar (correct)

Alumina and clay

Silica and zirconium oxide

What is the purpose of adding pigments to dental porcelain?

To produce hues similar to natural teeth (correct)

To enhance strength

To improve thermal conductivity

To increase melting points

Which component is NOT typically added to dental porcelain to modify its properties?

Glass modifiers

Zinc oxide (correct)

Opacifiers

Feldspar

What is the result of heating the mixture used in dental porcelain to a molten state?

It reacts chemically to create frit Signup and view all the answers

Which of the following is used to control the sintering temperature of dental porcelain?

Feldspar Signup and view all the answers

How does the addition of opacifiers affect dental porcelain?

Modifies transparency Signup and view all the answers

What is the purpose of quenching the molten ceramic mixture in water?

To cool and solidify it quickly Signup and view all the answers

What indicates that feldspar used in dental porcelain is typically colorless?

It requires pigments for coloration Signup and view all the answers

In the context of dental porcelain, what does the term 'frit' refer to?

The intermediate product after firing Signup and view all the answers

What role does silica play in the composition of dental porcelain?

It serves as the primary network formulator Signup and view all the answers

What is one of the main advantages of metal-ceramic (MC) restorations?

Lower fracture rate compared to full ceramic crowns Signup and view all the answers

Why is there a concern with a dark line at the facial margin of an MC crown?

It is associated with aesthetic issues during gingival recession Signup and view all the answers

What is a potential disadvantage of using MC crowns?

Potential for metal allergy reactions, particularly with nickel alloys Signup and view all the answers

What defines the high survival percentage of MC prostheses?

The use of high noble alloys Signup and view all the answers

Which factor affects the design choice of an MC crown to minimize aesthetic concerns?

Thickness of the metal collar Signup and view all the answers

When are MC crowns less commonly used?

In anterior restorations seeking high aesthetics Signup and view all the answers

What is the fracture rate of MC crowns and bridges made from high noble alloy after 7.5 years?

Less than 2.5% Signup and view all the answers

What is an indication for the use of MC crowns?

They are effective for multiunit or posterior fixed dental prostheses Signup and view all the answers

How can wear of antagonist enamel be compared when using MC crowns versus all-ceramic crowns?

MC crowns generally cause less wear of antagonist enamel Signup and view all the answers

What will enhance aesthetic results of MC crowns?

Implementing a polished ceramic margin Signup and view all the answers

Study Notes

Metal-Ceramic (MC) Prostheses

MC prostheses, also known as Porcelain Fused to Metal (PFM), show high overall survival rates in clinical studies. MC is the international standard.
Fracture rate of MC crowns and bridges made from high noble alloy is low (2.3%) after 7.5 years. Resistance to fracture is a key advantage.
Using metal on occlusal surfaces can reduce fracture rates further in posterior restorations.
MC restorations can require less tooth structure removal than all-ceramic restorations, especially when facial and buccal surfaces are porcelain and lingual and occlusal surfaces are metal, minimizing enamel wear on opposing teeth.
Dark lines at the facial margin of MC restorations are a concern with gingival recession.
Minimizing this issue involves ceramic margins (or very thin knife-edge metal margins veneered with opaque shoulder porcelain). Polishing/glazing is necessary.
Potential for metal allergies (rare, except possibly with nickel-based alloys) is a significant concern though less prominent in anterior areas.
All-ceramic crowns have improved in appearance, leading to MC crowns' decreased popularity in anterior restorations.
Indications are patient dependent, with dentist preference and occlusion playing a role. MC is more common in multi-unit or posterior fixed dental prostheses (FDPs).

Ceramic Types in MC

Conventional dental porcelain is a vitreous ceramic with a silica network and feldspar (potash or soda).
Ternary phase diagrams (e.g., K2O-Al2O3-SiO2) define the composition ranges for feldspathic porcelain, the most common MC ceramic type.
Dental feldspars are pure and colorless; pigments are added to achieve natural tooth shades.
Opacifiers and glass modifiers are included to control parameters like fusion/sintering temperature, thermal contraction, and solubility.
These ingredients are combined, heated (melted), cooled, and ground into fine powder (called frit).

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Description

This quiz delves into Metal-Ceramic (MC) prostheses, including their high survival rates and fracture resistance. You'll explore the benefits and considerations of using MC in dental restorations, such as preservation of tooth structure and concerns regarding aesthetic margins. Perfect for those studying dental materials and prosthodontics.