All ceramic-restoration

All Ceramic Restoration

By Dr- Tayseer Mohamed

All ceramic restoration

Porcelian fused to metal

Feldspathic porcelain

Porcelian baked on Ceramic crystalline core.

Porcelain baked on cast metal framework

Porcelian baked on platinm foil. Composed of 90% amorphous phase.

Used for anterior and posterior restoration.

Used for anterior and posterior restoration.

Used only for anterior crown.

Crystalline phase provids good strength and ideal esthetic.

Strong ductile metal copy withstand high forces but fracture and lack good esthetic.

Very brittle if used posteriorly occlusal forces subject them to tensile stress.

Ceramic restoration was developed to over come the dis-advatages of ceramo-metal restoration as.

1. lack of natural translucency.2. Bond failure.

It contains about 90 % by volume crystalline phases as reinforcing agents.

Advantages of all ceramic restorations

1. Superior esthetics.2. High biocompatible because it is inert.3. Low thermal conductivity: no thermal shock to the

prepared tooth.4. No electrolytic corrosion.5. No metal preparation: no metal inhaled during metal

finishing.6. Excellent bonding between the porcelain veneer and

ceramic coping.7. No repeated firing: no distortion of infra-structure.8. Resistant to degradation to oral fluids.

All ceramic systems according to various manufacturing techniques.

1. Sintered all ceramic restoration.2. Heat pressed all ceramic.3. Slip cast all ceramic.4. Machinable all ceramic

SINTERED ALL CERAMIC

1. Alumina-based Ceramics: Alumina has a high modulus of elasticity and

high fracture toughness. 40% stronger than traditional feldspathic

porcelain. It contains an opaque inner core containing

50% by weight alumina for high strength. Core is veneered with matched expansion

porcelain due to its inadequate translucency.

2. Leucite-based Ceramics: • Leucite(45%) in feldspathic porcelain

increases the flexural and compressive strength.

• The large mismatch in thermal contraction between leucite and the glass matrix causes development of compressive stresses in glass around the crystals so resistance to crack propagation.

Sintered all-ceramic restorations are now being replaced by heat-pressed or machined all-ceramic restorations with better-controlled processing steps.

HEAT PRESSED ALL CERAMIC

1. Leucite- based ceramics .2. Lithium disilicate based ceramics.

Heat-pressing requires a specially designed automated pressing furnace.

Heat-pressing relies on the application of external pressure at high temperature to sinter and shape the ceramic.

Ceramic ingots are brought to high temp in a phosphate-bonded investment mold produced

by the lost wax technique.A pressure of 0.3 to 0.4 MPa is then applied

through a refractory plunger. This allows filling of the mold with the softened ceramic.

• Increase in strength can be explained by the fact that these ceramics possess a higher crystallinity and that the heat-pressing process generates an excellent dispersion of these fine crystals.

• The main disadvantages are the initial cost of the equipment and relatively low strength compared with other all-ceramic systems

1. Leucite- based ceramics Ex: IPS Empress. This type contains leucite as a major

reinforcing crystalline phase dispersed in a glassy matrix.

Ceramic ingots are pressed at a higher temperature (1165°C) into a refractory mold made by lost wax technique.

2. Lithium disilicate based ceramics Ex: IPS Empress-2 The major crystalline phase of the core

material is Lithium disilicate. The material is pressed at 920°C and layered

with a glass containing some dispersed apatite crystals.

Their translucency is less than leucite-based ceramics and both have higher translucency than alumina based ceramics.

SLIP CAST ALL CERAMIC MATERIALS

1. In-ceram alumina. 2. In-ceram spinell .3. In-ceram zirconia.

Slip casting technique • Slip is an aqueous suspension of fine

ceramic particles in water.

• The slip is applied on to a porous refractory die that absorbs water from the slip by capillary action and leads to condensation of slip on the die.

The die with the slip are fired at high temperature.

The die shrinks more than the condensed slip which allows easy separation after firing.

• The fired porous core is then glass infiltrated (a process in which molten glass is drawn into the pores by capillary action at high temperature).

• Materials processed by slip-casting tend to exhibit lower porosity and fewer processing defects than do traditionally sintered ceramic materials.

• The strength of In-Ceram is about three to four times greater than that of earlier alumina core materials.

Slip casting technique

AB

c

a. In-ceram alumina The alumina content of the slip is more than

90% . First firing the slip, then porous alumina

coping is infiltrated with glass during a second firing . This processing leads to a high-strength material because of the presence of densely packed alumina particles.

The restoration is veneered using matched-expansion veneering ceramic.

• Because of the high strength of the core, short-span anterior fixed partial prostheses can be made using this process. However, the presence of alumina crystals with a high refractive index, together with 5% porosity, account for some degree of opacity in this all-ceramic system.

b. In-ceram spinel • It contains Magnesium spinel as a major crystalline

phase with traces of alumina.

• Spinel-based slip-cast ceramics are more translucent, because the spinel phase allows better sintering, but the flexural strength is slightly lower than that of the alumina-based system

• It is indicated for anterior crowns, inlays and onlays .

c. In-ceram zirconia Contains zirconia and alumina. It has the greatest levels of opacity and

should only be used in posterior regions as crowns or bridges.

It has the highest flexural strength among in-ceram types.

Machinable all ceramic restorations

• Machinable ceramics can be milled to form inlays, onlays and veneers using two systems:

1. CAD/CAM technology . 2. Copy milling .

a. CAD/CAM technology . The system refers to computer aided design/computer aided machining).

The system has an intraoral camera to take an optical impression of the prepared tooth.

The image is computerized. The restoration is designed with the aid of a computer. Then, the restoration is machined from ceramic blocks

by a computer-controlled milling machine which takes only few minutes.

• Advantages: 1. Obtaining an indirect restoration in one visit without

impression taking or need for temporary restoration. 2. No need for the dental lab to fabricate the

restoration. 3. No porosity as there is no firing.

• Disadvantages: 1. Expensive equipment. 2. Inadequate marginal inaccuracy .

b. COPY MILLED CERAMIC The primary difference between this and the

earlier system (CAD- CAM) is the manner in which the tooth dimensions are picked up. Coy milling scans the object whereas the Cad-Cam need digital impression.

In this system, a hard resin pattern is fabricated on a traditional stone die.

The pattern is placed in the machine. A tracing

tool passes over the pattern and guides a milling tool which grinds a copy of the pattern from a block of ceramic. Then it is veneered with porcelain and fired to complete the restoration.