DENTAL PORCELAIN

fusion

feldspar undergoes _______, it forms a glassy material, which gives porcelain its translucency.

FELDSPAR

acts as a matrix for the highfusing quartz, which then forms a refractory skeleton for the other materials to fuse around.

Quartz

a strengthener of dental porcelain

Aluminous Porcelain

This porcelain is considerably stronger than conventional porcelains.

Kaolin

a clay and sticky material that binds the particles together when the porcelain is "green" or unfired.

Silicone dioxide

(64-69%) SAPS

Aluminum oxide

(8-19%) SAPS

Potassium oxide

(8%) SAPS

Sodium oxide

(2-5%) SAPS

devitrify

When porcelain is fired too many times it can __

1. High-fusing porcelains

- used to manufacture DENTURE TEETH

2. Medium-fusing porcelains

- used for all-ceramic and porcelain jacket crowns.

3. Low-fusing porcelains

-used for metal-ceramic (PFM) crowns.

Aluminum oxide

- increase its resistance to "slumping down" during firing.

Calcium oxide

-also added to low-fusing porcelains.

potassium, sodium, and chromium

help reduce cross linkages between oxygen and silicone to lower the porcelain's fusing temperature. However, this also decreases the viscosity of the porcelain that may "slump down" during firing.

DEGASSING

- the process by which a casting is heated in a porcelain furnace to a temperature of 980°C to burn off any remaining impurities prior to adding porcelain.

Poor metal framework design

MAIN cause of fracture in PFM

decreasing the bond

Degassing of the metal at too low temperature effects formation of the oxide layer, thus

Feldspathic porcelain

-used for conventional porcelain-jacket crowns.

Aluminous porcelain

-found in Vitadur, Hyceram, Cerestore, & Inceram systems.

Alumina

is used to reinforce glass. Porcelain strength is determined by the amount of alumina reinforcement.

GLAZED PORCELAIN

This type of glaze is much more permanent than over glazes (applied glazes).

GLAZED PORCELAIN

is the LEAST IRRITATING to the gingival tissues compared to polished cast gold, polished direct filling gold, and polished acrylic resin.

OVER GLAZES (APPLIED GLAZES)

It is a ceramic powders that may be added to a porcelain restoration after it has been fired

OVER GLAZES (APPLIED GLAZES)

A transparent, glossy layer forms over the porcelain restoration surface at a maturing temperature lower than the body porcelain's temperature, resulting in a glossy or semi-glossy non-porous surface.

overglaze

Erosion of this _______ may occur in the mouth, leaving a rough and sometimes porous surface.

O.7mm

The absolute minimum required thickness of the porcelain is

O.3-0.5mm for high-noble gold alloys

Metal coping thickness can vary from

for base metal alloys

thickness

10°

The opposing walls should converge no greater than

0.5mm

The necessary thickness of metal substructure is

1-1.5mm

The minimal porcelain thickness is

1.5-2.0mm

tooth reduction required for a PFM crown is

1.5mm.

The labial shoulder width is ideally

inadequate condensation of the porcelain

The most common cause of porosity in the porcelain is

shape and size of the particle.

The effectiveness of condensing porcelain powder to reduce shrinkage is determined by the

green

Porcelain baked onto a high-fusing gold alloy may exhibit a _______ discoloration most likely due to metal contamination by copper traces.

IN THE PORCELAIN.

In metal-ceramic restorations, failure or fracture usually occurs

reater strength and resistance to fracture.

One of the major reasons for acceptance of the PFM restoration is its

inadequately designed framework

Repeated fracture of a porcelain-fused-to-metal restoration (PFM) is due primarily to

1. High-gold noble alloys:

used to fabricate metal-ceramic restorations (PFMs)

2. Palladium-Silver alloys:

50-60% palladium + 30-40% silver

oxidizes on casting

3. Nickel-Chromium alloys (base metal alloys):

70-80% nickel + 15% chromium.

These base metal alloys readily oxidize and can create porcelain-to-metal interface problems