There was always an intimate relation between metal and ceramic

material, Will this relationship will continue in the future?

Ceramics is a term refer to any product made from a nonmetallic inorganic material usually processed by firing at a high temperature.

Porcelain is s more restrictive term and refers to a specific compositional range of ceramic material originally made by mixing Kaolin ( hydrated aluminosilicate), quartz ( silica ), and feldspars (potassium and sodium aluminosilicates), and firing at high temperature.

All-ceramic inlays, onlays, veneers, and crowns can provide some

of the most esthetically A pleasing restorations currently available.

They can be made to match natural tooth structure accurately in

terms of color, surface texture, and translucency. Well-made all

ceramic restorations can be virtually indistinguishable from

unrestored natural teeth.

More recently, improved materials and techniques have been

introduced in an attempt to overcome disadvantages inherent in

that traditional method. These improvements, particularly the use

of higher strength ceramics and adhesives for bonding the ceramic

restoration to tooth structure.

Ceramic objects have been fabricated for thousands of years through

the attempts of Egyptian and Chinese.

More than two hundred years later was the first attempt to use

ceramics for making denture teeth was by Alexis Duchateau in 1774.

1887 C. H. Land made the first ceramic crowns and inlays with a

platinum foil matrix technique and was granted a patent. At that time

feldspathic porcelain used in the fabrication.

The popularity of ceramic restorations declined with the introduction of

acrylic resin in the 1940s and continued to be low until the

disadvantages of resin veneering materials (increased wear, high

permeability leading to discoloration and leakage) were realized.

In 1962 Weinstein and Weinstein patented a leucite-containing

porcelain frit for use in metalceramic restorations.

In 1965 McLean and Hughes advocated using aluminous porcelain,

which is composed of aluminum oxide (alumina) crystals dispersed in

a glassy matrix which is called ‘ High Strength Ceramics ‘

The chief disadvantage of the early restorations was their low

strength, which limited their use to low stress situations, such as those

encountered by anterior teeth. Even so, fracture was a fairly common

occurrence, which prompted the development of higher strength

materials.

These developments have included modifications to the microstructure

of the ceramic material during the manufacturing process, and the

development of different techniques to fabricate the product.

In spite of their excellent esthetic qualities and outstanding

biocompatibility, dental ceramics, like all ceramic materials, are brittle.

They are susceptible to fracture at the time of placement and during

function. Brittle materials such as ceramics contain at least two types

of flaws: fabrication defects and surface cracks, from which fracture

can initiate.

Fabrication Defects

Fabrication defects are created during processing and consist of :

o voids or inclusions generated during sintering. Condensation of a

ceramic slurry by hand before sintering may introduce porosity.

Sintering under vacuum reduces the porosity in dental ceramics

from 5.6 to 0.56 volume percent.

o Also, microcracks develop within the ceramic upon cooling in

leucite-containing ceramics and are caused by thermal contraction

mismatch between the crystals and the glassy matrix.

Surface Cracks

Surface cracks are induced by machining or grinding. The average

natural flaw size varies from 20 to 50 µm. Usually, fracture of the

ceramic material takes place from the most severe flaw.

The principle of toughening by crystalline reinforcement is to increase

the resistance of the ceramic to crack propagation by introducing a

dispersed crystalline phase with high toughness.

Crystals can acts as crack deflector when their coefficient of thermal

expansion is greater than that of the surrounding glassy matrix,

placing them under a tangential compressive stresses after the

ceramic has been cooled to room temperature.

Transformation toughening is obtained, for example, in ceramics

containing partially stabilized tetragonal zirconia.

Zirconia (ZrO2) exists under several crystallographic forms. Zirconia

is monoclinic at room temperature and tetragonal between about

1170° C and 2370° C. The transformation between tetragonal and

monoclinic zirconia is accompanied by an increase in volume. The

tetragonal form can be retained at room temperature by addition of

various oxides such as yttrium oxide ( Y2O3) or cerium oxide (CeO2).

Stress can trigger the transformation from tetragonal (3Y-TZP) to

monoclinic zirconia, thereby leading to strengthening as a result of an

increase in grain volume in the vicinity of the crack tip.

chemical strengthening relies on the replacement of small ions with larger ions by diffusion from a molten salt bath in which the ceramic or glass is immersed.

the exchange leads to the creation of a compressive layer at the surface of the ceramic.‘ Finally, any applied load must first overcome this built-in compression layer before the surface can be placed into tension; this results in an increase in fracture resistance.

• Tempering is obtained by using rapid but controlled cooling.

• This also create a compressive stress layer at the surface of a glass

or a ceramics.

• Although widely used in the glass industry, neither of these two

techniques is used for dental ceramics.

The principle is the formation of a low-

expansion surface layer formed at a high

temperature. Upon cooling, the low-

expansion glaze places the surface of the

ceramic in compression and reduces the

depth and width of surface flaws

standard technique, also called self-

glazing, does not significantly improve the

flexural strength of feldspathic dental

porcelains. However, a low-expansion

glass called glaze can also be applied at

the surface of the ceramic.

Alumina-Based Ceramic

Alumina-Based Ceramic was first introduced

to dentistry by McLean and Hughes in 1965.

Alumina-Based Ceramic is composed of

aluminum oxide (alumina) crystals dispersed

in a glassy matrix.

The technique involved the use of an opaque inner core containing 50% by weight alumina

for high strength. This core was veneered by

a combination of esthetic body and enamel

porcelains with 15% and 5% crystalline

alumina, respectively

The flexure strength approximately twice that

of feldspathic porcelains (139 to 145 MPa).

Leucite-Reinforced Ceramic

Leucite-reinforced ceramics containing up to 45% by volume tetragonal leucite the greater leucite content leads to higher flexural strength (104 MPa) and compressive strength.

Because the crystals contract more than the surrounding glassy matrix, this results in the development of tangential compressive stresses in the glass around the leucite crystals. These stresses can act as crack deflectors and contribute to increased resistance of the ceramic to crack propagation

Heat-pressed ceramics have been popular in restorative dentistry since

the early 1990s. The restorations are waxed, invested, and pressed in a

manner somewhat similar to that for gold casting.

Leucite-Based Ceramic

• First-generation heat-pressed ceramics contain leucite (KAlSi2O6 or K2O • Al2O3 •

4SiO2) as a reinforcing phase, in amounts varying from 35% to 55% by volume.

• Heat-pressing temperatures )1150° and 1180° C).

• The crystal size varies from 1 to 5 µm.

• The amount of porosity is 9 vol%.

• The flexural strength of these ceramics (120 MPa).

Two techniques are available

A staining technique (surface stain only) and a layering technique involving the application of veneering ceramic.

Disadvantages

• The initial high cost of the equipment.

• The relatively low strength.

materials for heat-pressing are

IPS Empress, Optimal Pressable Ceramic, and two lower fusing

materials, Cerpress and Finesses

Lithium Disilicate–Based Materials

• The second generation of heat-pressed ceramics contain lithium disilicate (Li2Si2O5) as a major crystalline Phase.

• Heat-pressing temperatures (890° to 920° C).

• The final microstructure consists of about 65% by volume of highly interlocking prismatic lithium disilicate crystals.

• The amount of porosity is 1 vol%.

the main advantage is their enhanced flexural strength (300 MPa) and fracture toughness (2.9 MPa • m0.5).

Applications --------- < Anterior fixed partial prostheses.

• IPS Empress 2 is an example for lithium disilicate, IPA Empress Cosmo is an example for lithium phosphate.

• Slip-casting was introduced in dentistry in the1990s

• The first step of the process involves the condensation of a porcelain

aqueous slurry slip on a refractory die.

• The porosity of the refractory die helps condensation by absorbing the

water from the slip by capillary action

• The restoration is incrementally built up, shaped, and finally sintered

at high temperature on the refractory die.

Alumina and Spinel-Based Slip-Cast Ceramics

It consists of 68 vol% alumina, 27 vol% glass, and 5 vol% Porosity

The flexural strength is around 600 MPa

Spinel-based slip-cast ceramics are more translucent, because the spinel phase

allows better sintering, but the flexural strength is slightly lower (378 MPa) than

that of the alumina-based system.

In Ceram, In Ceram Spinell, In Ceram Cosmo is an example

Application : short-span anterior fixed partial prostheses

Zirconia-Toughened Alumina Slip-Cast Ceramics

• It consists of 34 vol% alumina, 33 vol% zirconia stabilized with 12 mol% ceria

(12Ce-TZP), 23 vol% glassy phase, and 8 vol% residual porosity

• The combination of alumina and zirconia allows two types of strengthening Mechanisms

• The flexural strength : 630 Mpa

Advantage --------- < high strength

Disadvantages --------- <high opacity (with the exception of the spinel-based

materials)

• The evolution of computer-aided

design/computer-aided

manufacturer (or computer-

assisted machining) (CAD/CAM)

systems for the production of

machined inlays, onlays, veneers,

and crowns led to the development

of a new generation of ceramics

that are machinable.

Hard Machining

• Machinable ceramics can be milled to form inlays, onlays, veneers, and

crowns using CAD/ CAM technology to produce restorations in one office

visit.

• After the tooth is prepared, the preparation is optically scanned and the

image is computerized. The restoration is designed with the aid of a

computer, as shown in. The restoration is then machined from ceramic

blocks by a computer-controlled milling machine. The milling process takes

only a few minutes.

• Feldspar, leucite, and lithium disilicate–based ceramic blocks are available in

the market

Soft Machining Followed by Sintering

The CAD/CAM and copy-milling systems can also be used to machine

presintered alumina, spinel, or zirconia-toughened-alumina blocks.

Advantages : The blocks are easy to mill, which leads to substantial

savings in time and tool wear

grain size of 0.2 to 0.7 μm

sintering temperature 1350° to 1550° C

durations from 2 to 6 hours

flexural strength (900-1500 MPa)

fracture toughness (greater than 5 MPa • m0.5)

Dental CAD/CAM systems consist of three components:

1. A scanner or digitizing instrument that transforms physical

geometry into digital data.

2. Software that processes the scanned data an creates images of

the digitized object. Some systems then enable restorations to be

designed for the digitized object.

3. Fabrication technology that transforms the digital data of the

restoration into a physical product. Different systems place the

fabrication technology in the dental office, dental laboratory, or

centralized facility.

copy milling (Celay®, Mikrona Technologie AG) :

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

This handmade pattern is then copied and machined from a ceramic

block using a pantographic device similar in principle to those used for

duplicating house keys.

Cerec system

• The Cerec system has been marketed

since the 1980s, with the improved

Cerec 2 system introduced in the mid-

1990s and the Cerec 3 in 2000.

• Several materials can be used with this

system: VITA Mark II, ProCad s and In-

Ceram Alumina and Spinell.

• VITA Mark II contains feldspar, ProCad is a leucite-containing ceramic

• Weaknesses of the earlier Cerec

system include the poor marginal fit of the restorations and the lack of

sophistication in the machining of the

occlusal surface, but these weakness

have overcomed in Cerec 3.

Procera AllCeram system

• The Procera AllCeram system involves

an industrial CAD/CAM process.

• The die is mechanically scanned by the

technician, and the data are sent to a

work station, where an enlarged die is

milled by a computer-controlled milling

machine.

• The restorations seem to have good

clinical performance and marginal

adaptation provided that the scanning

is done skillfully.

In a 10-year study of 308 ceramic restorations placed in 74 patients between 1991 and

1994, the restoration survival rate was 94.7% after 5 years and 85.7% after 10 years,

which is comparable to the survival rates of cast gold restorations.

A systematic review of studies that reported on single-tooth restorations fabricated with

CAD/CAM technology from 1985 to 2007 revealed a failure rate of 1.75% per year,

calculated per 100 restoration years from a total of 1957 restorations and a mean

exposure time of 7.9 years. The review estimated a total 5-year survival rate of 91.6%.

the unique mechanical properties of 3Y-TZP, making possible the realization of both single

and multiunit anterior and posterior restorations.

PORCELAIN LABIAL VENEER

Porcelain labial veneers can be fabricated by means of a refractory die

technique, as well as on a platinum matrix and with heat-pressed-ceramics.

'Porcelain labial veneers can also be made with the machinable systems.

Lumineers®, is one brand of porcelain veneer. These veneers are made out

of porcelain named Cerinate®. And because Cerinate® is exceptionally

strong, Lumineers® veneers can be made to extremely thin tolerances (on

the same order as the thickness of a contact lens).

Den-Mat Corporation (the manufacturer) promotes placement using a

protocol that involves no drilling, no shoots dental aesthatic.

The thickness of a Lumineer® veneer can be as little as 0.2 to 0.3

millimeters

The most ideal candidates for having Lumineers® veneers placed using

a "no drilling" technique are typically those people whose teeth are ...

o already relatively straight in alignment.

o and only require a slight color or other cosmetic change.

o Additional beneficial conditions include teeth that are relatively

small, lingually inclined or have spaces between them.

INLAYS AND ONLAYS

Refractory Dies Ceramic restorations are normally made through the

use of the heat-pressed systems, but some technicians prefer a

refractory Marginal adaptation can be excellent, depending more on

the technician's skill than on the ceramic material used.

ALL-CERAMIC PARTIAL FIXED DENTAL PROSTHESES

All-ceramic FDPs have a checkered history. Their construction was

attempted with aluminous porcelain by connecting alumina cores with

pure alumina rods. These restorations were usually unsuccessful:

either they fractured or the restorations encroached excessively into

the embrasures, resulting in hygiene deficiencies.

ALL-CERAMIC FOUNDATION RESTORATIONS

All-ceramic materials have been used as foundation restorations for

endodontically treated teeth to overcome esthetic problems

associated with metal post and core systems. The post is made of

zirconia, chosen for its excellent strength, and depending on the

system, the core material can be composite resin or a pressable

ceramic.