With the advent of all-ceramic restoration modalities, allowing for a simultaneous fabrication of both ceramic framework and porcelain veneer, modern cosmetic dentistry could benefit from a selection of the ideal all-ceramic structures encompassing both function and aesthetics. Silicate ceramics could be used in porcelain laminate veneers and crowns in the anterior region to provide excellent aesthetics.
Silicate ceramics could be used in porcelain laminate veneers and crowns in the anterior region to provide excellent aesthetics. Whereas, Oxide ceramics, specifically Zirconium Oxide ceramics, are used in the posterior area, where functional forces require higher flexural strength.
The IPS e.max ceramic system, excelling the IPS Empress 2 system, combines the advantages of the Zirconium Oxide ceramics (ZrO2), e.g. IPS e.max Zircad, with the excellent aesthetic qualities of Silicate ceramics, e.g. IPS e.max Press.
This article describes the diverse clinical, mechanical, aesthetical, and laboratory-related characteristics of all-ceramic Substructures respective Supra-structures utilised in modern cosmetic dentistry.
All-ceramic systems are classified according to the fabrication techniques, which may include:
I. The whole restoration:
IA. Feldspathic ceramics
IB. Pressed ceramics
IC. In-surgery CAD/CAM (CEREC ®= CEramic REConstruction)
II. A coping to which glass-ceramic is layered or pressed
IIA. Alumina-based systems (In-Ceram®, Tech-Ceram®, Procera All-Ceram®)
IIB. Zirconium-based system (Porcelain fused to CAD/CAM Zirconia coping)
I. The whole restoration:
IA. Feldspathic Porcelains (Dentin/Resin-bonded crowns/veneers)
The feldspathic porcelain is fired onto a refractory or platinum foil die by layering (stacking). The all-ceramic restoration is bonded to underlying dentin/enamel using dual-cure resin-based luting cement with the mediating bond created by dentin bonding agents and micro mechanically retentive ceramic surface (Burke 1996). They require good moister control rendering subgingival margins a relative contraindication. Fortress® is a leucite-reinforced system with increased fracture resistance and opacity due to leucite crystals.
Indications: Anterior single veneers and crowns where minimal biomechanical demand exists.
Advantages: a) Conservative tooth preparation, b) Customised/localised Blockout of underlying colours, c) Good depth of colour, d) Unlimited colour stratification, e) Relatively inexpensive, f) Chameleon effect as the restoration takes some of its colour from the underlying and adjacent tooth structure.
Disadvantages: a) Low flexural strength, b) Can not evaluate full shape/contour until the end versus low-fusing porcelain, c) Feldspathic porcelain may wear antagonists, d) More difficult for a technician to master, e) Not indicated for dark underlying restorations/tooth structure.
IB. Pressed Porcelains (Empress®, Cerpress®, Authentic®, Matchmaker®)
The full-contoured wax-up is invested and boiled out (lost-wax technique). The molten leucite-reinforced porcelain is pressed in, de-vested and de-sprouted. The pressed restoration is then characterised by surface staining or cutting-back and layering followed by glazing.
Indications: Single units
Advantages: Can evaluate full shape/ contour prior to pressing, better long term marginal integrity, can be fabricated quickly, stronger than feldspathic.
Sorenson et al. (1998) reported a 97% success rate for Empress Crowns during a 3-year clinical study.
Disadvantages: Cut-back for layering may reduce strength, difficult to mask the dark preparations, difficult to apply to stain.
IB1. Empress I®
Leucite reinforced ceramic powder in a glass matrix which is sintered, heated and softened and then pressed or cast into the invested and burnt-out mould made of initial wax-up.
Indications: Inlays, Onlays, veneers and crowns
Advantages: strength and resistance to crack propagation due to leucite crystals.
IB2. Empress II®
Lithium disilicate reinforced ceramic powder in a glass matrix which is sintered and pressed.
Advantage: Increased strength
Indications: Inlays, Onlays, veneers and crowns, 3- units-bridge anterior to molar regions.
Two techniques may be applied to fabricate empress restorations:
1. The staining technique: Cast or pressed restoration, which is equal to the full shape wax-up, is devested and stained.
2. The layering technique: The pressed restoration, which is smaller than the full shape wax-up, is devested and veneered over.
IC. In-surgery CAD-CAM (CEREC®=Ceramic REConstruction)
An optical impression of the tooth preparation is made on the basis of which the restoration is designed on a computer and milled at chair-side followed by staining and glazing.
Indications: Single unit restorations; veneers and single front crowns with minimal biomechanical demand
Advantages: One visit procedure, strength similar to pressed
Disadvantages: a) Big investment in equipment, single units only, b) Staining and glazing can be time-consuming and difficult to master
II. A coping to which glass-ceramic is layered or pressed:
IIA. Alumina-based systems (In-Ceram®, Tech-Ceram®, Procera All-Ceram®)
Conventional porcelain is veneered on a high alumina content core all-ceramic coping. They present with high opacity and strength. Aluminium oxide is a stable material that does not change in the oral cavity (Oden et al. 1991). Evaluation of mechanical properties of dense sintered pure Alumina reveals the flexural strength of Procera all-Ceram: 650MPa, In-Ceram 450MPa and Empress: 160MPa (Zeng & Rowcliffe, 1991).
IIA1. In-Ceram®
Glass infiltrated Aluminium Oxide.
Porous pre-sintered Aluminium-Oxide is infiltrated by heat-treated Glass powder. Then the feldspathic porcelain is veneered on the high alumina-content coping. This system has 450MPa bi-flexural strength and is indicated for anterior/posterior single crowns and anterior short span bridges.
There are three types of In-Cram core available based on the content of a) Alumina content (70% Alumina for strength), b) mixture of Alumina and Magnesia, which offers less strength but better aesthetics due to twice more translucency (Spinell), C) mixture of Alumina and Zirconia, which offers more strength. McLaren and white (2000) presented a 3-year 96% clinical survival rate for In-Ceram crowns showing a higher survival rate for anterior (98%) vs posterior (94%) crowns.
IIA2. Tech-Ceram®
Flame-sprayed Alumina particles onto a refractory model before sintering
A translucent or coloured base layer with 8 different shades (made by Tech-Ceram laboratory) is veneered with Vita Alpha porcelain. This system has 300MPa bi-flexural strength and indicated for anterior/posterior single crowns and inlays.
IIA3. Procera All-Ceram®
Non-porous Densely-sintered Alumina core
The scanned image of the master die is electronically sent to the manufacturer. The core substructure (coping) is made of dense glass infiltrated alumina compacted onto the enlarged die and sintered at 1,600C. The coping is shipped back from Sweden to the local laboratory to be veneered by aluminous porcelain. This system has 680MPa bi-flexural strength and is indicated for anterior/posterior single crowns and anterior short span bridges.
Indications: Crowns, short span front bridge
Advantages: a) High strength (Procera = 2x In-Ceram, 5x Empress), b) Excellent masking ability, c) no concerns with cement discolouration or of luting cement.
Disadvantages: a) Quite opaque, require a more aggressive preparation to avoid cervical opaque appearance, b) Not aesthetic when supragingival margins, c) Preparation surfaces must be rounded to be scanned, d) longer turnaround time.
IIB. Zirconia-based systems (Porcelain fused to CAD/CAM Zirconia coping)
Pressed Porcelains (Empress®, Cerpress®, Authentic®, Matchmaker®)
The full-contoured wax-up is invested and boiled out (lost-wax technique). The molten leucite-reinforced porcelain is pressed in, devested and de-sprouted. The pressed restoration is then characterised by surface staining or cutting-back and layering followed by glazing.
Indication: Single units
Advantages: a) Can evaluate full shape/ contour prior to pressing, b) Better long term marginal integrity, c) can be fabricated quickly, stronger than feldspathic.
Sorenson et al. (1998) reported a 97% success rate for Empress Crowns during a 3-year clinical study.
Disadvantages: a) Cut-back for layering may reduce strength, b) Difficult to mask the dark preparations, c) Difficult to apply to stain.
IIB1. Empress II®
Lithium disilicate reinforced ceramic powder in a glass matrix which is sintered and pressed.
Advantages: Increased strength
Indication: Inlays, Onlays, veneers and crowns, 3- units-bridge anterior to molar regions.
Two techniques may be applied to fabricate empress restorations:
I. The staining technique: The cast, or pressed restoration, which is equal to the full shape wax-up, is devested and stained.
II. The layering technique: The pressed restoration, which is smaller than the full shape wax-up, is devested and veneered over.
IIB2. Empress IPS e-max all ceramic®
Advantages:
- High strength materials, i.e. high strength zirconium oxide & glass-ceramic
- Outstanding aesthetics and shade matching
- A combination of press and CAD/CAM fabrication techniques optimise both strengths and fit
- The layering ceramic technique optimises the natural appearance and aesthetics
The versatility and simplicity of the system offer the following structural combination:
I. Substructures
IA. e.max CAD: High strength glass-ceramic block CAD/CAM
Indications: a) Substructure for single-unit anterior, premolar, b) Superstructure for single-tooth implant.
Advantages: a) Translucent and semi-translucent substructure block for superior aesthetic, b) Optimised restorative fit due to absence of shrinkage, c) Flexural strength of over 360 MPA.
IB. e.max Zir CAD®: High strength pre-sintered, yttrium-stabilised zirconium oxide block CAD/CAM
Indications: a) Substructures for high strength crowns, b) Substructure for 3- or 4-unit bridge and inlay-retained bridges.
Advantages: a) Biocompatibility, b) Flexural strength of over 900 MPA offers fracture toughness more than twice that of the glass-infiltrated ceramic ingot, c) Resistance to crack propagation, d) Long-term stability.
IC. IPS e.max Press®: High strength glass-ceramic ingot
Indication: a) Substructure for anterior and posterior single tooth crown, b) Substructure for an anterior 3-unit bridge, c) Superstructure for single-tooth implant.
Advantage: a) Ultimate in fit, strength and aesthetics due to applied pressable technology, b) Flexural strength of over 400 MPA
II. Superstructures
IIA. IPS e. max Ceram®: Nano- Fluor-apatite layering ceramic
Indications: a) Layered on all e-max components, b) Layered on most commonly used zirconium oxide substructures, c) Layered veneers.
Advantage: a) Excellent aesthetics, b) Predictable shade matching even with difficult combination cases.
IIB. IPS e.max Zir.Press: Fluor-apatite glass ceramic
Indication: Cut-back technique and fully anatomical technique
Advantages
- Pressed Fluor-apatite glass-ceramic to zirconium offers both of the advantages of superior fit in pressable ceramic and superior strength in zirconium.
- Enhanced detailed occlusal anatomy using a wax-up technique.
- Optimised occlusion using the wax build-up techniques.
IIC. Lava System®
In the milling centre, the prepared teeth, edentulous alveolar ridge on the model and possibly the bite registration is optically scanned to produce a digitised image using light triangulation with a measuring accuracy of 20um. The restoration is designed by Lava-CAD. The CAM milling machine then produces an enlarged framework structure from the pre-sintered blank block of green state soft Zirconia. After processing, the structure will be sintered and shrunk back to the exact original size due to its known exact coefficient value. The second technique is copy milling of the Zirconia core (Cercon with “ivory” coloured substructure) and the third method of manufacture involves milling a very hard fully processed pre-shrunken Zirconia to fit the die (Preci-fit).
Advantages:
- Inhibits crack propagation due to the Yttrium-meta- stabilised tetragonal poly-crystalline form of Zirconium which displays phase transformation by providing high initial strength, fracture toughness and resistance to stress fatigue when subjected to static and/or dynamic stress.
- Available in 0.5mm thickness for the posterior, and 0.3mm thickness for the anterior application.
- Due to the high strength, an anterior 0.3mm-thick Lava coping would offer an increased relative translucency and facilitates utilisation of both conventional and adhesive translucent cement.
- Due to high strength, correct connector design with reduced dimension (9SQmm) in single units and 3/4-unit fixed bridges allows the creation of embrasures with more natural profile and enough space for the soft tissue management and hygiene requirement.
- Predictable marginal fit, ranging from 25-100um.
- The thermal expansion coefficient of especially-developed overlay porcelain (Lava Ceram) compatible with that of Zirconium coping.
- Seven chromatically stable VITA shades address the problem with inadequate aesthetic translucency due to being too bright with extremely high value.
- The incorporation of colour in its fabrication at the green stage (pre-sintered state) means no compromise to its strength.
- The equivalent base colour of dentin substrate and the coping eliminate the need for toning down and layering with opaque porcelain due to copings’ high value
- Lava-Ceram porcelain has a high degree of homogeneity and surface quality which provides excellent opalescence and translucency properties.
Discussion
Diverse ceramic systems have different mechanical, physical and optical properties which render them unique and appropriate in applications in a selected clinical restorative situation. The use of CAD/CAM and copy milling of core material as well as pressed ceramic is increasing. Despite some limitation, all-Ceramic restorations when selected and applied correctly, present excellent aesthetic, biological, physical and mechanical properties resulting to outstanding clinical outcome.
The clinician should evaluate each restorative case individually and decide upon the appropriate choice of the all-ceramic system fulfilling the requirement with regard to versatility, strength, prep conservativeness, the choice of luting cement/bonding system, opacity to mask prep darkness/ discolouration, turnaround time/speed of production.
Strength
PFM/Press to metal > Cercon/Lava > Procera > Inceram > Captec > Pressed > Feldspatic
Prep conservativeness
Feldspatic > pressed > Captec/ Press to metal > PFM / Inceram / Procera > Cercon/Lava
Opacity to mask prep darkness/ discolouration
PFM/Captec/Press to metal > Cercon/Lava > Procera > Inceram > Feldspathic
Turnaround time/ speed of production
Pressed > Feldspathic > PFM/Captec/Press to metal > Inceram > Procera > Cercon/Lava
- All-ceramic systems have recently progressed both in terms of physical and aesthetical characteristic providing a choice of framework porcelains as well as the veneer where an ideal structure with regard to both function and aesthetics is required (Román-Rodríguez et al. 2009).
- While Silicate ceramics allow the application of the porcelain laminate veneers and crowns in the anterior region where excellent aesthetics is required, oxide ceramics, specifically zirconium oxide, are the choice of material for the posterior area, where function precede pure aesthetics.
- The IPS e.max ceramic system, developed from the generation of the IPS Empress 2 system, have successfully combined the physical advantages of zirconium oxide ceramics (IPS e.max Zircad) with the aesthetic qualities of silicate ceramics e.g. IPS e.max Press (Román-Rodríguez et al. 2009).
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