www.rxdentistry.net. metal free ceramics
TRANSCRIPT
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METAL FREE CERAMICS
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CONTENTS
1. Introduction2. Classification3. Conventional powder slurry systems4. Castable ceramics5. Pressable ceramics6. Infiltrable ceramics7. Machinable ceramics8. Recent advances 9. Conclusion10.Bibliography
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The term ‘ceramics’ is derived from the greek word ‘keramos’ meaning burnt stuff. The first ceramics fabricated by man were ‘Earthenware’ pots used for domestic purposes. This material is opaque, relatively weak and porous . It consisted mainly of kaolin. The blending of this with other minerals such as silica and feldspar produce the translucency and extra strength required for dental restorations. This was given the name ‘porcelain’.
INTRODUCTION
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Historically, strength concerns compromised some of the esthetics of the porcelain crowns. Because of the relatively low tensile strength and brittleness of the porcelain it has been generally fused to metal substrate to increase resistance to fracture. However this metal base can effect the esthetics of the porcelain by decreasing the light transmission through the porcelain and by creating metal ion discoloration, allergic reaction and sensitivity.These drawbacks together with the material and labour costs associated with metal substrate fabrication have promoted the development of new ceramic systems that do not require metal yet have the strength and precision fit.So with the increasing demand for esthetics, improvements in strength of ceramics and adhesives for bonding of ceramics, metal free ceramics have become an important part of contemporary dental practice.
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CLASSIFICATION
1. Conventional / powder slurry
systems
2. Castable ceramics
3. Pressable ceramics
4. Infiltrated ceramics
5. Machinable ceramicswww.rxdentistry.net
Conventional / powder slurry systems- PORCELAIN JACKET CROWN
- PJC with Aluminous core
- Glass ceramics
- Leucite reinforced porcelain (OPTEC HSP)
- DUCERAM LFC
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PORCELAIN JACKET CROWN
Dr Charles Land introduced one of the first
ceramic crowns in dentistry in 1903.
Used a platinum foil matrix and high fusing
feldspathic porcelain.
Excellent esthetics but low flexural strength:
half moon fracture.
Poor marginal adaptation.
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PLATINUM FOIL TECHNIQUE
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PJC with Aluminous core
Mc Lean and Hughes developed a PJC with an alumina reinforced core in 1965 which resulted in significant improvement in fracture resistance
It consisted of a glass matrix containing between 40-50 wt% of Al2O3.
Large sintering shrinkage (15-20%) and use of foil - excellent marginal adaptation difficult to achieve.
Inadequate translucency.
The principle indication: maxillary anterior crown restoration
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Glass-ceramics polycrystalline materials developed for application by casting procedures using the lost wax technique.
Glass ceramics partially crystallized glass
crystalline and amorphous properties
Fabricated in the vitreous (Glass or non-crystalline/amorphous) state and converted to a ceramic (crystalline state) by controlled crystallization using nucleating agents during heat treatment.
Glass ceramics
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Feldspathic porcelain higher leucite crystal content.
The leucite and glassy components are fused during the baking process…at 1020ºC.
Leucite reinforced porcelain (OPTEC HSP)
ADVANTAGES: 1. More esthetic due to a more translucent core. 2. Greater strength. 3. No special processing equipment required.
DRAWBACKS: 1. Increased leucite content contributes to the relatively high in vitro wear of opposing teeth. 2. Potential marginal inaccuracy USES: Inlays,onlays,low stress crowns.
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DUCERAM LFC
In 1992 duceram lfc was marketed as an ultralow fusing ceramic with 3 unique features:
1. Hydrothermal glass:decrease in glass transition temp., increase in flexural strength and thermal expansion co efficient.
2. “Self healing”…forming a 1 micrometer thick hydrothermal layer.
3. Extremely small size of crystal particles…enhances opalescence of ceramics.
USES: Inlays,veneers,full contour crowns.
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CASTABLE CERAMICS www.rxdentistry.net
CASTABLE CERAMICS:
I. FLUOROMICAS
eg: Dicor
II. APATITE GLASS CERAMICS
eg: Cerapearl (bioceram)
III. OTHER GLASS CERAMICS
… Lithia based … Calcium phosphate based
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Dicor, the first commercially available castable glass-ceramic material for dental use was developed by The Corning Glass Works and marketed by Dentsply International The term “DICOR” is a combination of the manufacturer’s names: Dentsply International & Corning glass.
Dicor is a castable polycrystalline fluorine containing tetrasilicic mica glass-ceramic (55 vol%) material, initially cast as a glass by a lost-wax technique and subsequently heat - treated resulting in a controlled crystallization to produce a glass - ceramic material.
DICOR
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Excellent esthetics resulting from natural translucency, light absorption, light refraction and natural colour for the restoration.(Chameleon effect)
Relatively high strength (reported flexural strength of 152 MPa), surface hardness (abrasion resistance) and occlusal wear similar to enamel.
Inherent resistance to bacterial plaque and biocompatible with surrounding tissues.
Low thermal conductivity. Excellent marginal adaptation
ADVANTAGES
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Requires special and expensive equipments
Laboratory studies for use as veneers and inlays, failure rates as high as 8% in the posterior region
Dicor must be shaded/ stained with low fusing feldspathic shading porcelain to achieve acceptable esthetics, however the entire stain/ colors maybe lost during occlusal adjustment (use of abrasives), during routine dental prophylaxis or through the use of acidulated fluoride gels.
DISADVANTAGES
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CASTABLE APATITE GLASS CERAMIC1985 -Sumiya Hobo & Iwata …available as Cera Pearl.
Chemistry: Apatite glass-ceramic melts (1460°C) and flows like molten glass and when cast (1510°C) it has an amorphous microstructure
Desirable characteristics of Apatite Ceramics Cerapearl is similar to natural enamel in
composition, density, refractive index, coefficient of thermal expansion and hardness
Bonding to tooth structure www.rxdentistry.net
Lithia Based Glass-Ceramic
Developed by Uryu
Commercially available as Olympus Castable Ceramic (OCC)
Composition: It contains crystals of LiO.AI2O3.4SiO2 after heat treatment.
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Given by Kihara and others, for fabrication of all-ceramic crowns by the lost wax technique.
It is a combination of calcium phosphate and phosphorus pentoxide plus trace elements.
The glass ceramic is cast at 1050°C which is converted to a crystalline ceramic by heat treating at 645°C for 12 hours.
Reported Flexural strength (116 Mpa); Hardness close to tooth structure.
Disadvantages Weaker than other castable ceramics Opacity reduces the indication for use in anterior
teeth.
Calcium Phosphate Glass-Ceramic
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High strength because of controlled particle size reinforcement.
Excellent esthetics resulting from light transmission similar to that of natural teeth .and convenient procedures for imparting the required colour.
Accurate form for occlusion, proximal contacts, and marginal adaptation.
Uniformity and purity of the material.
Advantages of castable glass ceramics
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Hardness and wear properties closely matched to those of natural enamel
Similar thermal conductivity and thermal expansion to natural enamel
Dimensional stability regardless of any porcelain corrective procedure and subsequent firings
Favorable soft tissue response.
X-ray density allowing examination by radiograph
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PRESSABLE CERAMICS(Heat transfer molded or Injection molded)
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PRESSABLE CERAMICS
1.Shrink free ceramics: eg Cerestore Al-ceram
2.Leucite reinforced glass ceramics: eg IPS empress Optec/OPC
3.Lithia reinforced glass ceramic: eg IPS empress 2 OPC 3G
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CERESTORE
This shrink-free ceramic material essentially consists of Al2O3 and MgO mixed with a Barium glass frits. On firing crystalline transformation produces Magnesium aluminate spinel, which occupies a greater volume than the original mixed oxides compensates for the conventional firing shrinkage.
Good dimensional stability
Better accuracy of fit and marginal integrity.
Esthetics enhanced due to the lack of metal coping.
Biocompatible .
Low thermal conductivity, Low coefficient of thermal
expansion
Advantages:
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Complexity of the fabrication process.
Need for specialized laboratory equipment
Inadequate flexural strength (89MPa)
Poor abrasion resistance, hence not recommended in patients with heavy bruxism or inadequate clearance.
Limitations and high clinical failure rates led to its withdrawal from the market. It underwent further improvement with a 70 to 90% higher flexural strength and was marketed under the commercial name Al Ceram
Disadvantages :
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Recrystallization of residual glass – Fracture toughness 22.5 MN/m2 (32,000psi)
High polycrystalline content
Same relative thermal conductivity of core and veneer porcelain
Low coefficient of thermal expansion - Thermal shock resistance.
High modulus of elasticity - Low stress on cement.
AL CERAM
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First described by Wohlwend & Scharer;
Is a precerammed glass ceramic having a high concentration of leucite crystals ie.35 vol%(KAlSi2O6).
It increases the resistance to crack propogation.
The manufacturer blends it with resin blocks,being thermoplastic allows the material to be injection molded. Leucite-reinforced ceramic powder available in different shades is pressed into ingots and sintered.
The ingots are heated in the pressing furnace until molten and then injected into the investment mold.
IPS EMPRESS
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Properties :
Reported flexural strengths are in the range of 160 to I80MPa.
The increase in strength has been attributed to the pressing step which increases the density of leucite crystals.
Subsequent heat treatments which initiate growth of additional leucite crystals.
Uses :
Laminate veneers and full crowns for anterior teeth
Inlays, Onlays and partial coverage crowns
Complete crowns on posterior teeth.
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Lack of metal or an opaque ceramic core
Moderate flexural strength (120-180MPa range)
Excellent fit (low-shrinkage ceramic)
Improved esthetics (translucent, fluorescence)
Etchable
Less susceptible to fatigue and stress failure
Less abrasive to opposing tooth
Biocompatible material
Unlike previous glass-ceramic systems IPS Empress does not require ceramming to initiate the crystalline phase of leucite crystals (They are formed throughout the various temperature cycles).
ADVANTAGES
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Second generation of pressable materials for all-ceramic bridges.
Lithium disilicate framework with an apatite layered ceramic.
The glass-ceramic ingots are made from lithium silicate glass crystals with crystal content of more than 70 volume%.
The apatite crystals incorporated are responsible for the improved optical properties (translucency, light scattering) unique chameleon effect.
IPS Empress 2 is used with special investment material, an EP500 press furnace and a fully automatic high-tech furnace.
IPS EMPRESS 2
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High biocompatibility Excellent fracture resistance High radiopacity Outstanding translucency.
Uses :Anterior and posterior crown
Premolar FPD.
Other applications : Cosmopost and IPS Empress cosmoingot - core build-up system with the pre-fabricated zircon oxide root canal posts and the optimally coordinated ingot.
ADVANTAGES
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INFILTRATED CERAMICS
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GLASS INFILTRATED CORE PORCELAINS
1. INCERAM ALUMINA
2. INCERAM SPINELL
3. INCERAM ZIRCONIA
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An improved high aluminous porcelain system termed In-Ceram was developed by a French scientist and dentist Dr. Michael Sadoun (1980) and first introduced in France in 1988.
INCERAM
Composition:
Alumina/ Al203 crystalline
An Infiltration glass lanthanum aluminosilicate with small amounts of sodium and calcium
Final ICA core contains 70 wt% alumina infiltrated with 30 wt% sodium lanthanum glass.
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Uses: Single anterior & posterior crowns
Anterior 3-unit FPD's
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Advantages : Minimal firing shrinkage, hence an accurate fit.
High flexure strength (almost 3 times of ordinary porcelain) makes the material suitable even for multiple-unit bridges
Aluminous core being opaque can be used to cover darkened teeth or post/ core.
Wear of opposing teeth is lesser than with conventional porcelains.
Improved esthetics due to lack of metal as substructure.
Biocompatible, diminished plaque accumulation, biochemical stability.
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Disadvantages : Requires specialized equipment
Poor optical properties.
Incapability of being etched with HF acid.
Slip casting is a complex technique and requires considerable practice.
Requires considerable reduction of tooth surface all over for adequate thickness of restoration.
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This is an offshoot of Inceram alumina.
Due to the comparatively high opacity of the alumina core,this material was introduced .
Incorporating magnesium aluminate (Mg A1204) results in improved optical properties characterized by increased translucency with about 25% reduction in flexural strength.
Spinel or Magnesium aluminate (Mg A12O4) is a composition containing Al2O3 and Mg2O (a natural oxide of Mg2+ AI3+).
In-Ceram Spinell
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ADVANTAGE:
Increased translucency provides improved esthetics in clinical situations in which the adjacent teeth or restorations are quite translucent.
DISADVANTAGES:
Lower strength and toughness.
USES:
Anterior inlay, onlay ,veneers
and anterior crowns.
Incapable to be etched by HF
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The In-Ceram technique was expanded to include its modified form with zirconia.
A mixture of zirconium oxide/ aluminium oxide is used as a framework material, the physical properties were improved without altering the proven working procedure.
The final core of ICZ consists of 30 wt% zirconia and 70 wt% alumina.
In-Ceram Zirconia
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ADVANTAGES: The In-Ceram Zirconia material is said to feature
a high flexural strength 700 MPa (2 to 3 times the impact capacity as the ln-Ceram Alumina), excellent marginal accuracy and bicompatibility.
DISADVANTAGE: Poor esthetics due to increased opacity. Inability to etch.
USES: Posterior crowns and FPD’s.
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MACHINABLE
CERAMICS
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Regardless of the advanced state of the 300-year old technique of casting, each of its steps could induce error in the final casting.
Until 1988, indirect ceramic dental restorations were fabricated by conventional methods (sintering, casting and pressing) and neither were pore-free.
Pore-free restorations can be alternately produced by machining blocks of pore-free industrial quality ceramic.
The tremendous advances in computers and robotics could also be applied to revolutionize dentistry and provide both precision and reduce time consumption.
With the combination of optoelectronics, computer techniques and sinter-technology, the morphologic shape of crowns can be sculpted in an automated way.
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MACHINING SYSTEM
CAD-CAM(DIGITAL) COPYING SYSTEMS (ANALOGOUS)
DIRECT
• Cerec 1
• Cerec 2
INDIRECT
• Automill
• Denti CAD
COPY MILLING EROSION
1.MANUAL 1.SONOEROSION eg:Celay eg:DFE Erosonic
2.AUTOMATIC 2.SPARK EROSION eg:Ceramatic eg:DFE Procera
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Uses digital information about the tooth preparation or a pattern of the restoration to provide a computer-aided design (CAD) on the video monitor for inspection and modification.
The image is the reference for designing a restoration on the video monitor.
Once the 3-D image for the restoration design is accepted, the computer translates the image into a set of instructions to guide a milling tool (computer-assisted manufacturing [CAM]) in cutting the restoration from a block of material.
DIGITAL SYSTEMS
CAD-CAM:
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Stages of fabrication: All systems ideally involve 5 basic stages:
1. Computerized surface digitization
2. Computer - aided design
3. Computer - assisted manufacturing
4. Computer - aided esthetics
5. Computer - aided finishing
(The last two stages are more complex and are still being developed for including in commercial systems).
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The CEREC (Ceramic Reconstruction) was originally developed by Brains AG in Switzerland. Identified as CEREC CAD/CAM system, it was manufactured in West Germany
Cerec System consists of :
A 3-D video camera (scan head)
An electronic image processor (video processor) with memory unit (contour memory)
A digital processor (computer) connected to,
A miniature milling machine (3-axis machine)
CEREC SYSTEM
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CERAC Computer,3D camera and milling unit
3D Impression
3D Porcelain restoration
Millingwww.rxdentistry.net
Clinical shortcoming of Cerec 1 system:
Although the CEREC system generated all internal and external aspects of the restoration, the occlusal anatomy had to be developed by the clinician using a flame-shaped, fine-particle diamond instrument and conventional porcelain polishing procedures were required to finalize the restoration.
Inaccuracy of fit or large interfacial gaps.
Clinical fracture related to insufficient depth of preparation.
Relatively poor esthetics due to the uniform colour and lack of characterization in the materials used.
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The Cerec 2 unit was introduced in September 1994, and is the result of constant further development via different generations of Cerec units to eliminate the previous limitations.
The major changes include :
Enlargement of the grinding unit from 3 axis to 6 axis.
Upgrading of the software with more sophisticated technology which allows machining of the occlusal surfaces for the occlusion and the complex machining of the floor parts.
Cerec 2 system
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Data representation in the image memory and processing increased by 8 times
Magnification factor increased from x8 to x12 for improved accuracy during measurements.
Monitor can be swiveled and tilted, thus facilitating visual control of the video image.
Other technical innovations of Cerec 2 compared to Cerec 1: The improved Cerec 2 camera : new design, easy to
handle, a detachable cover (asepsis), reduction in the pixel
Improved in rigidity and grinding precision
Improved accuracy of fitwww.rxdentistry.net
Machinable Ceramics The industrially prefabricated ceramic ingots/
blank used are practically pore-free which do not require high temperature processing and glazing, hence have a consistently high quality.
The blanks measure approximately 9 x 9 x 13 mm and are industrially fabricated using conventional dental porcelain techniques.
Frit powder is mixed with distilled water, condensed into a 10 x 10 x l5 mm steel die and fired under vacuum
Two classes of machinable ceramics available are:
Fine-scale feldspathic porcelain
Glass-ceramics www.rxdentistry.net
Ceramic CAD/ CAM restorations are bonded to tooth structure by :
Etching for a bond to enamel
Conditioning, priming and bonding (when appropriate)
Etching (by HF acid) and priming (silanating)
Cementing with luting resin. Properties:
Excellent fracture and wear resistance
Pore-free
Possess both crystalline and non-crystalline phase (a 2-phase composition permits differential etching of the internal surface for bonding).
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PROCERA ALLCERAM
• It is composed of densely sintered, high purity aluminium oxide core combined with a compatable all ceram veneering porcelain
• 99.9% alumina and its hardness is one of the highest among the ceramics used in dentistry.
• A unique feature of the procera system is the ability of the procera scanner to scan the surface of the prepared tooth and transmit the data to the milling unit to produce an enlarged die through a CAD-CAM processer.
• The core ceramic is dry pressed on to the die, sintered and veneered.
• Thus the 15-20% shrinkage during sintering will be compensated, which will shrink during sintering to the desired size to give an accurate fit.
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USES: Anterior and posterior crowns
Veneers, onays and inlays.
Ceramic abutment for implant supported single crowns
Aluminium oxide core Veneering porcelain
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Other machinable ceramics include:
Bioglass
DFE
Empress / Vivadent
MGC -F
Pro CAD
Celay
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The clinical advantages of the Cerec system:
The restorations made from prefabricated and optimized, quality-controlled ceramic porcelain can be placed in one visit.
Translucency and color of porcelain very closely approximate the natural hard dental tissues.
Further, the quality of the ceramic porcelain is not changed by the variations that may occur during processing in dental laboratories.
The prefabricated ceramic is wear resistant.
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OTHER DIGITAL SYSTEMS:
THE COMET SYSTEM
The Duret System (Hanson International):
The SOPHA System
The REKOW Svstem
The Denti CAD svstem
The DUX system/The Titan System
CICERO System (Computer Integrated Crown Reconstruction)
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Eliminates impression model making and fabrication of temporary prosthesis.
Dentist controls the manufacturing of the restoration entirely without laboratory assistance.
Single visit restoration and good patient acceptance.
Alternative materials can be used, since milling is not limited to castable materials.
The use of CAD/ CAM system has helped provide void free porcelain restorations, without firing shrinkage and with better adaptation.
ADVATAGES OVER OTHER SYSTEMS
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Eliminates the asepsis link between the patient, the dentist, operational field and ceramist.
The shapes created in the CAD unit
are well defined, and modifications
can be carried out on the display screen
itself .
Glazing is not required and can easily be polished.
Minimal abrasion of opposing tooth structure
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Limitations in the fabrication of multiple units.
Inability to characterize shades and translucency.
Inability to image in a wet environment
Incompatibility with other imaging system.
Extremely expensive and limited availability.
Few long-term studies on the durability of the restorations.
DISADVANTAGES
Lack of computer-controlled processing support for occlusal adjustment.
Technique sensitive www.rxdentistry.net
The Celay System became first commercially available in 1992. It is a high precision, manually operated copy milling machine and the fabrication principle is the same as for 'Key' duplication.
The fabrication of copy-milled In-Ceram crown substructures with the Celay system combines the positive mechanical properties of glass-infiltrated aluminous core materials with the advantages of industrially prefabricated ceramics.
CELAY System
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Advantage of milling methods :
Reducing the labour time needed.
Single appointment restorations (in a period of 3 to 13 minutes).
Can be used for both direct and indirect fabrications.
Advantages of Celay system over the Cerec system :
Celay could recreate all surfaces of a restoration whereas Cerec I could not make the occlusal surface.
Celay has the potential to fabricate crowns and short-span bridges with In-Ceram system (Vita, Germany).
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Criteria for selection and use of dental ceramics:
1. Not to use in patients with extreme bruxism, clenching and malocclusions.
2. Degree of wear of tooth or restoration.3. Bite force capability.4. Any previous history of all ceramic inlay/crowm
fracture.5. Experience of laboratory technician should be
extensive.6. Esthetic demands of specific patient.7. Degree of translucency of adjacent teeth.8. Skill of dentist is of paramount importance.
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EXTENDED & INNOVATIVE APPLICATIONS OF CERAMICS IN DENTISTRY
Posterior esthetic restorations (Inlay & Onlays)
All-Ceramic Post & Core systems (Zirconia ceramics)
In Dental Implants:
Ceramic coating for dental implants
Implant supported ceramic restorations
Ceramic Orthodontic Brackets
Ceramics for Oral Mucosal Stimulation Silanized ceramic fibres in Ceromers (Eg: Targis)
As fillers www.rxdentistry.net
RECENT ADVANCES IN METAL FREE CERAMICS
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LITHIUM DISILICATE
Glass ceramics are categorized according to their major crystalline structure and/or application. Lithium disilicate is among the best known and most widely used types of glass ceramics. IPS e.max (Ivoclar Vivadent) lithium disilicate, for example, is composed of quartz, lithium dioxide, phosphor oxide, alumina, potassium oxide, and other components . Overall, this composition yields a highly thermal shock resistant glass ceramic due to the low thermal expansion that results when it is processed. This type of resistant glass ceramic can be processed using either well-known lost-wax hot pressing techniques or state-of-the-art CAD/CAM milling procedures.
IPS e.max Press (Ivoclar Vivadent) lithium disilicate. . IPS e.max CAD (Ivoclar Vivadent) lithium
disilicate.www.rxdentistry.net
Table 1. Properties of IPS e.max Press.
CTE (100-400°C [10-6/K] 10.2
CTE (100-500°C) [10-6/K] 10.5
Flexible strength (biaxial) [MPa] 400
Fracture toughness [MPa m0.5] 2.75
Modulus of elasticity [GPa] 95
Vickers hardness [MPa] 5,800
Chemical resistance [µg/cm2 40
Press temperature EP 600 [°C] 915 to 920
Table 2. Properties of IPS e.max CAD.
CTE (100-400°C [10-6/K] 10.2
CTE (100-500°C) [10-6/K] 10.5
Flexible strength (biaxial) [MPa] 360
Fracture toughness [MPa m0.5 2.25
Modulus of elasticity [GPa] 95
Vickers hardness [MPa] 5,800
Chemical solubility [µg/cm2 40
Crystallization temperature [°C] 840 to 850
Indications for the machinable lithium disilicate material are inlays, onlays, veneers, partial crowns, anterior and posterior crowns, telescope primary crowns, and implant restorations For a posterior crown fabricated to full contour using CAD methods, lithium disilicate offers 360 MPa of strength through the entire restoration. As a result, restorations demonstrate a “monolithic” strength unlike any other metal or metal-free restoration.Overall, these materials demonstrate specific advantages to dentists and patients, including higher edge strength versus traditional glass ceramic materials (ie, can be finished thinner) low viscosity of heated ingot enables pressing to very thin dimension (ie, enabling minimal prep or no prep veneers); and chameleon effect due to higher translucency
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Wol-Ceram is the first ceramic crown that allows you to prepare a conservative feather-edge or chamfer margin. Copings are made from Vita In-Ceram alumina material, which has been proven in clinical tests for over 12 years. The outstanding fit and strength are the result of the Electrophoretic ceramic process resulting in excellent marginal integrity. Wol-Ceram’s beautifully natural esthetics result from a dentin colored coping that prevents opaque show-through.
Lava delivers the strength you’ve been looking for in an esthetic all-ceramic restoration. The Lava system combines CAD/CAM technology with a translucent zirconia framework that can be custom colored creating a restoration strong enough for long span bridges, with precise fit and esthetics your patients expect.
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MACOR Machineable Glass Ceramic
MACOR® Machineable Glass Ceramic has a continuous use temperature of 800ºC and a peak temperature of 1000ºC. Its coefficient of thermal expansion readily matches most metals and sealing glasses.It is non-wetting, exhibits zero porosity, and unlike ductile materials, won't deform. It is an excellent insulator at high voltages, various frequencies and high temperatures. When properly baked out, it won't outgas in vacuum environments.
It can be machined into complicated shapes and precision parts with ordinary metal working tools, quickly and inexpensively, and it requires no post firing after machining. That means no frustrating delays, no expensive hardware, no post fabrication shrinkage, and no costly diamond tools to meet specifications.
Typical characteristics include:
Zero porosity and non-shrinking High dielectric strength Electrical resistivity Withstands high temperatures up to 1000ºC Tight tolerance capability
Easily and economically machined into complex shapes and precision parts www.rxdentistry.net
Dental ceramic technology is one of the fastest growing areas of dental material research and development. The past decades have seen the development of several new groups of ceramics.
The diversity of dental ceramics continues to stimulate laboratory and clinical research. Systems such as Dicor and Empress are now established.
The potential of the In-Ceram system, remains to be exploited to the full.
The diversity and sophistication of some of the CAD-CAM systems may prove to be influential in the future.
CONCLUSION
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Each system has its own merits, but may also have shortcomings. Combinations of materials and techniques are beginning to emerge which aim to exploit the best features of each. Glass-ceramic and glass-infiltrated alumina blocks for CAD-CAM restoration production are examples of these and it is anticipated that this trend is likely to continue….
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Bibliography
• Philips science of dental materials{10th and 11th edition}• Review of All ceramic restorations: JADA 1997;128:297• Recent advances in restorative dental ceramics: JADA
1993;124:72• A new method : CAD-CAM system: JADA 1989;118:703• Slip casting alumina ceramics for crown and bridge
restorations: Quintessence international 1992;23:1 Heat pressed ceramics:technology and strength: IJP 1999;5
• Procera All ceramic crowns: BDJ 1999;186:430• Porcelain esthetics for 21 st century: JADA 2000;131:47
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• Relative flexural strength of 6 new ceramic materials: IJP 1995;8:239
• Machinable glass ceramics and conventional lab restorations: Quint Int 1994;25:773
• Ceramics in dentistry:Historical roots and current perspective: JPD 1996;75
• Heat pressed ceramics:technology and strength: IJP 1999;5
• Procera All ceramic crowns: BDJ 1999;186:430• Porcelain esthetics for 21 st century: JADA 2000;131:47
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THANK YOU
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