Denial Ceramic

Question 1

STRUCTURE OF DENTAL PORCELAIN

Question 2

Why use ceramics?

Answer 2

Appeal of dental ceramics is:
- corrosion resistance (relative insolubility in the mouth)
- surface hardness.
- aesthetics.

Question 3

Dental porcelains

Answer 3

produced as glass powders featuring particle sizes ranging 1-80 microns.
- the system is non-crystalline and acts as a super-cooled liquid of high viscosity at room temperature.
- structural basis can be understood in terms of vitreous (glass-like) silica SiO2, which has been chemically modified to yield suitable physical and chemical properties.
- modifying agents is normally an oxide, the principal functions of which can be broadly categorised as follows:

Question 4

Modifying agents

Answer 4

1. NETWORK-MODIFYING OXIDES
2. NETWORK-FORMING OXIDES
3. OPACIFENT OXIDES
4. FLUORESCENT OXIDES
   Dental porcelain is produced from the fusion of appropriate ratios of these (& other) components,
   followed by fritting and grinding to a powder with a suitable range of particle sizes.

Question 5

In the dental production laboratory

Answer 5

Heat a suitably-shaped agglomerate of porcelain particles to the fusion temperature (ca 950-9800C). Known as ‘firing
•Resulting in fusion of the individual particles without porosity.
•The physical process is one of SINTERING and the driving force is the accompanying reduction of surface energy.
• A volume contraction accompanies the firing process, which may be up to 30%.

Question 6

Sintering

Answer 6

Sintering is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction. Sintering happens naturally in mineral deposits or as a manufacturing process used with metals, ceramics, plastics, and other materials.

Question 7

To fabricate a porcelain crown or an enamel veneer,

Question 8

Dental porcelain

Answer 8

Brittle material.
•As with all brittle materials tensile strength is reduced from the theoretical value by the presence of flaws such as cracks & pores
•These defects may be on the surface, or within the body of the material.
•Internal porosity may be reduced by firing in a partial vacuum
VACUUM-FIRED PORCELAIN, with improved aesthetics and strength.
Termed as maturity