Ceramics were first used in dentistry in 1774 to replace previously used natural substances such as ivory, bone, wood, natural teeth or cadaver human teeth. Though the use of ceramics solved the problems associated with natural materials such as odour, staining, decay and wear, the aesthetics with porcelain of this age were of poor quality.

Over the past 200 years, scientists have worked to improve the physical and esthetic qualities of porcelain. Advancement in the areas of colour, translucency, opalescence, wear properties, and fracture resistance have lead to the creation of exceptional products that are both lifelike and natural in terms of their esthetics, wear and longevity.

In the past dental porcelains were mainly feldspathic in origin. Today there is an assortment of porcelain types that include leucite re-enforcement, (I.e. Empress, Finess All Ceramic, Fortress) sintered aluminous porcelain (I.e. Procera, Inceram) and glass castings (Dicor) and Zirconia

Categorization of the vast array of ceramics available in the dental marketplace is a challenge. Upon further examination, the clinician will learn that a product, which carries a proprietary name, does not necessarily represent only one porcelain, but may actually represent several different types of porcelain. An example of this is the Empress system by Ivoclar. In this system, there are several different products each represented by the same proprietary name. This system includes core porcelains, a veneer porcelain etc. In order to avoid confusion or mistakes, the clinician must be informed and very familiar with the specific products that he or she wishes to use.

In spite of the confusion present in the marketplace, the following is a simple categorization of dental ceramics. This categorization will help the clinician determine not only which ceramic is indicated to provide the best restoration for your patient, but also help determine the best means of luting the chosen restoration.

In this system of categorization of ceramics, there are three basic groups of All-Ceramic Restorations.

Types of Porcelain:

1. Metal Ceramics
2. Conventional Ceramics
3. Non Conventional Ceramics

Conventional Ceramics:

1. Feldspathic
2. Aluminous
3. Low fusing
4. Pressed (glass)
5. High strength ceramics
6. Glass infused
7. Optimized composites
8. Polyglasses/ceromers

Mechanical Requirements:

1. location
2. substrate attachment mechanic
3. wear resistances
4. non abrasive
5. physical properties

Esthetic Requirements:

1. ease of fabrication
2. match optical properties to natural teeth
3. maintain polish

Biologic Materials:

1. Biocompatibility
2. Pulpal considerations
3. Conservation of teeth structure
4. Corrosion resistance

• Aluminous Oxide Core, All Ceramic Restorations
• Non-Aluminous Oxide Core, All Ceramic Restorations
• Veneer Porcelains

Aluminous Oxide Core, All Ceramic Restorations

In these restorations, the aluminous oxide core or substructure is used to replace the metal substructure used in conventional porcelain fused to metal restorations (PFM’s). The elimination of the metal substructure yields greater translucency and vastly improved esthetics compared to the conventional PFM’s. Though the fracture resistance is inferior to PFM’s, these restorations have flexural strengths in the range of 600-800 Mpa, which is approximately twice that of all ceramic restoration, which do not have an aluminous oxide core. Due to their inherent greater strength, aluminous core porcelain restorations offer the advantage of not requiring bonding to maximize strength. They also can be luted with conventional cements such as zinc phosphate cement or glass ionomer cements. This is particularly advantageous in situations where moisture control is difficult. An added advantage to these restorations is that they can be tried in and left in place in the patient’s mouth with temporary or soft cement to allow for a trial patient evaluation.

Non-Aluminous, All Ceramic Restorations

The terminology of Non Aluminous most simply describes these restorations, as they share similar properties such as strength, luting mechanisms and translucency. These restorations are all ceramic but their cores are made from a material other than Aluminum Oxide. These restorations may have cores fabricated from materials such as pressed leucite as is found in Empress, lithium disilicate found in Empress 2, or non-pressed, Leucite re-inforced cores, such as can be found in Fortress. Because these restorations lack an aluminous core, they yield more translucent and esthetic restorations than can usually, they be achieved with aluminous core restorations. However, they derive their maximum strengths from the bonding process, and (with the exception of Empress 2,) and can not be left in the patient’s mouth temporarily for try in, nor can they be utilized where moisture control during the luting procedure is questionable.

Veneer Porcelains

This is the third category of porcelain. These ceramics are designed to provide the outer layer (veneer) on a metal core, aluminous core or non-Aluminous core substructure. Many of these ceramics can also be used as stand alone restorations such as porcelain veneers.

When used free standing, as in a veneer fabrication, the stacked or conventional feldspathic porcelains can be fired to a thinner margin and require less preparation than pressed or cast ceramic systems which required more tooth preparation. However, the pressed or cast ceramic systems yield greater strengths.

Definitions and Properties:
Surface Hardness:

• The closer porcelain can be to the surface hardness of Enamel, the less wear will occur on the opposing natural dentition
• Determined by the Vickers Hardness Test. (This is determined by applying the point of pyramidal shaped diamonds to the surface of the tested material. The resulting impression is measured to determine the results)
• Natural enamel has a surface hardness of 300HV (Hardness Vickers)
• Manufacturers often confuse hardness with abrasivity. Hardness is actually how the material itself will wear, while abrasivity is how it will wear the opposing surface.

Abrasivity:

• Often confused with Surface Hardness
• Major improvements have occurred in this area
• Abrasivity measures the wear on the opposing dentition
• Conventional feldspathic porcelains have high abrasivity and are becoming obsolete

Marginal Integrity:

Generally, pressed systems have better marginal adaptation than conventional stacked or feldspathic porcelains, and demonstrate less distortion with repeated firing.

Flexural Strength:

• Determines the ability to withstand direct forces before permanent deformation or fracture
• Measures brittleness
• Normal chewing delivers forces of 60-250 N
• Parafunction delivers forces of 500-800N
• Porcelains must have a high flexural strength to prevent fracture

Chemical Durability: ISO standards testing of chemical durability call for porcelain to be boiled in 4% Acetic acid for 16 hours, followed by comparison weight of before and after boiling

Fluorescence: Natural teeth are fluorescent. This means that they emit visible light when exposed to UV light. Fluorescence adds to the vitality of the tooth and minimizes metamerism

Opalescence:

• A natural property of enamel
• Occurs when transmitted light yields a yellow-orange hue and reflected light yields a blue hue
• Provides the restoration with a vivid appearance
• Conventional porcelains lack this property but it is present in some newer porcelains.

Leucite:

Present in most dental porcelains, It is an artificial feldspathic crystal: K2O,Al2O34SiO2. This is created in the heating process by the conversion of feldspar crystals into glass and leucite. Leucite is added to porcelains to increase their co-efficient of thermal expansion. This is because the thermal expansion of glass is 8 ppm/0C and dental alloys is about 14 ppm/0C. As the co-efficient of thermal expansion for Leucite is 22-25 ppm/0C, its addition to glass can help to control the rate of expansion to match that of the dental alloys.

Leucite is traditionally found at a rate of 35-40% in traditional high fusing porcelains. Large crystals and high content of leucite cause high fusing porcelains to be abrasive. Lower leucite content and smaller leucite crystals of low fusing porcelains leads to high polishablility and less abrasiveness

Low Fusing Porcelains:

• Fabricated to demonstrate low abrasivity
• Fine grained
• Demonstrates fluorescence and opalescence
• Require firing temperatures of 940 degrees C.
• Fires at temperatures approx. 200 degrees below firing temperature required by conventional porcelains
• Low leucite and small particle size facilitates chairside polishing

Major Manufacturers:

• Degussa: Golden Gate System with Hydrothermal Porcelain, Ducera Procera Porcelain, Duceram Plus, and Duceram LFC
• Ivoclar: Empress, Empress 2, d-Sign
• Vita: Inceram Alumina and Inceram Spinell and Inceram Zirconia, Omega 900, Vitadur Alpha
• Dentsply/Ceramaco: Finesse, Finesse All Ceramic, Ceramco II
• Nobel Biocare: Procera
• Mirage: Fortress Pressable, Fortress All Ceramic (designed specifically for use in porcelain veneers), Fortress Gold (for use on high gold alloys) and Fortress PFM
• Jensen: Willi Geller’s Creation, Sunrise
• Jeneric Pentron: OPC (optimal Pressable Ceramic) Optec, Optec HSP

Characteristic of Manufacturer’s Porcelain Types:

Degussa:

Degussa Hydrothermal Porcelain: while all ceramics have limited amount of Hydrothermal Porcelain, Degussa has a patented hydrothermal product called Duceram LFC (Low Fusing Ceramic). This ceramic is referred to as Hydrothermal Porcelain because of its substitution of hydroxyl ions for alkaline ions in the oral environment. This yields a more fluid surface, which in turn covers and ‘heals’ the microscopic flaws, which in turn yields an increase in strength.

These porcelains are actually glasses due to the absence of the crystal phase. Hydrothermal porcelains have a surface hardness of 420 HV while conventional ceramics have a surface hardness approaching 600 HV. This is advantageous, as this helps prevent wear of the opposing natural dentition

Hydrothermal Porcelains have a homogeneous and dense structure making it easy to grind and polish. This contributes to the materials extremely smooth surface, which yields reduced plaque adherence and subsequent gingival inflammation

Hydrothermal ceramics exceed the ISO minimum standard for Flexural strength and shown to increase their flexural strength by up to 40% in intraoral fluids due to plastification of the outer 3 microns due to the formation of Si Hydroxyl groups

Hydrothermal ceramics also exhibit a high level of transparency and natural opalescence.

These porcelains actually soften at increased temperatures such as during polishing yielding easier grinding and polishing. They can also be added to margin porcelain to yield a smoother, less irritating porcelain margin.

Degussa also produces another Hydrothermal Porcelain called Ducera Gold, designed to be used with Degunorm, their high noble type IV gold.

Ivoclar/Williams Empress 2

• 3X the strength of IPS Empress and can be used for 3 unit bridges which extend no more posterior than the second bicuspid
• Core is made from Lithium DiSilicate which is 60-80% crystal but still maintains translucency due to a similar refractive index of Lithium DiSilicate crystals to that of a glassy matrix
• Restorations from Empress 2 and Empress have demonstrated marginal fits within 30-70 microns
• Veneer Porcelain is made from Fluorapatite glass ceramic
• Somewhat more opaque than Empress
• In the posterior, pontic span must be restricted to 9 mm, but this can be extended to 11 mm in the anterior regions of the mouth.
• Internal surfaces are etchable
• These restorations can be cemented (Manufacturer recommends their product of ProTec CEM), but derive increased strength from bonding to teeth.
• Manufacturer claims flexural strength of 300 Mpa (Empress has strengths of 120-130 Mpa)
• Veneer Porcelain is made from Fluorapatite crystals (sintered glass-ceramic) which a needle shaped, similar to the crystals found in natural human enamel
• Mimics natural opalescence and fluorescence
• Requires only 1.0 mm of axial reduction compared to 1.4-1.7 for PFMs and 1.3 for IPS Empress (if bonded rather than cemented)
• Requires long connector in gingival-incisal direction of bridges to minimize fracture: connector must be 5.0 mm in length and 4.5 mm in width in the premolar area and 4.0 x 4.0 mm in the anterior region

Vita All Porcelain Systems:

Inceram Spinell:

• MgAl2 O4 which is the formulation Inceram Spinell, is also the formulation for naturally occurring spinells
• Spinells have a high melting point of 2135 degrees C.
• Used in conjunction with Vitadur Alpha porcelain layering porcelain
• Useful for anterior crowns, inlays, onlays
• Greater translucency than Inceram Alumina
• Flexural Strength of 350 Mpa
• Achieves a marginal fit of 20-35 microns

Inceram Alumina:

• 3 times strength of regular all porcelain systems
• Flexural strength of 500 Mpa
• Can be used for 3 unit all ceramic anterior bridges
• Achieves a marginal fit of 20-35 microns
• Less translucent than Inceram Spinell
• Used in conjunction with Vitadur N or Vitadur Alpha layering porcelain

Both Inceram Spinell and Inceram Alumina use the sintering process.

Inceram Zirconia:

Newly introduced to the North American market, no long term North American studies are currently available though this product has been tested in Europe for the past 8 years.

• Can be used for posterior single crowns or bridges
• 700 Mpa Flexural Strength
• Less translucent than Inceram alumina
• Very difficult to cut, therefore removal can be very challenging for the clinician

All Inceram products can be cemented with zinc phosphate, composite adhesives or glass ionomers

Ceramco: Finesse Porcelain

• Can be used as a veneer porcelain on metal or on All Ceramic (Finesse All- Ceramic)
• Conventional porcelains gain opacity as the shade becomes darker, and excessive translucency can occur with the lighter shades. However, Finess uses Infinite Optical Thickness technology to control the translucency and opacity.
• Finesse also has opal enamels, which are said to exhibit optimal opalescence, which yields the appearance of yellow-orange in transmitted light and blue in reflected light.
• Finesse demonstrates less wear against enamel than conventional feldspathic porcelain though whether this is clinically significant remains to be determined
• Leucite re-inforced silicate glass
• Can be pressed to full contour with out the cut-back technique and be stained to finish the restoration without the use of Finess Layering Porcelain
• Uses ultra fine leucite crystals in a glass matrix
• Not indicated for use on molars
• Can be used with pressable ceramic cores or high content gold alloys
• All components of the Finess all Ceramic fluoresce
• Finess all Ceramic is not indicated for use on molars

Nobel Biocare/Degussa: Procera

• Dies are computer scanned and transmitted to core fabrication centre where the cores are manufactured by CAD/CAM technology
• Cores are fabricated from sintered aluminum oxide and veneered with Procera All Ceram, manufactured by Degussa
• Strengths much higher than conventional porcelains or leucite reinforced pressed ceramics (Empress) Manufacturer claims flexural strengths of approx. 600 Mpa
• May be cemented as opposed to bonded in situations where bonding is not possible due to access or moisture control
• Copings may be as thin as .5-.6 mm
• Marginal openings range from 55-80 microns
• Requires specific tooth preparation designs to allow for proper scanning (apically angled chamfer)

Mirage: Fortress

• High strength
• Leucite reinforced
• Minimal metamerism due to glass refractive index identical to leucite crystals
• Used as all ceramic restorations

Dentsply/Ceramco: Colorlogic

• Veneer porcelain
• Uses high chroma porcelain to provide more colour in a thin veneer
• Uses opalescent incisal porcelains to increase vitality of restoration
• Good choice for PBM’s

Jensen Industries: Creation and Surprise

• Designed to be used in multi-layered buildup technique
• Highly fluorescent shoulder, opaceous dentins and internal colour modifiers

Jeneric Pentron: OPC

• Pressed ceramic with reduced size of leucite crystals, which improves the crystalline component and therefore the strength
• Found to be stronger than Empress in at least one study with fits equal to or superior to Empress (30-70 microns)
• Now comes with low wear veneering porcelain
• Strengths similar to Empress at 120-140 Mpa

Extra notes

• Empress is high fusing yet low wear
• Conventional porcelain is leucite crystals imbedded in glass matrix
• In small crystals- when leucite crystals cool there is less resultant shrinkage which helps to prevent micro cracks
• Large leucite crystals in feldspathic porcelains are very abrasive
• There is really very little difference in the composition between Empress and Feldspathic except for the size of the leucite crystals at the micro structural levels
• The term Feldspathic refers to the naturally occurring leucite crystals which are large, Empress has artificially produced leucite crystals which a much smaller therefore less abrasive
• Low fusing Porcelain is good for very thin veneers I.e.: Omega 900, dSign (850 degrees), Finesse.
• Glass Ceramics: Dicor, Empress 1, OPC Finesse Authentic: All have glass matrix with tetra silica mica
• Interpenetrating Material: Inceram Alumina, Spinell and Zirconia all are 85% crystallization with glass matrix.
• Empress 2 has 60% crystalline matrix
• Empress Crowns: Should keep core material on the occlusal surface because the core material has less wear than the veneer material
• New Procera has a translucent core. Therefore if one wants maximum translucency, use: Empress1, Translucent Procera and Inceram Spinell.
• Underlying Tooth Structure:
• Use translucent porcelains at margins and on surface of core to mask out darkness.
• If Discoloured substrate present, use older more opaque Procera or air infiltrated Spinell which is more opaque due to the tiny air bubbles (‘)
• Procera can be 0.3 mm thick on labial while pressed glass must be 0.8 mm thick
• Procera should be 0.7 mm on lingual.
• Procera should be thinned out with Brasseler Dialite Blue wheels to be adjusted or new diamond. Do not over heat therefore must blow air while reducing
• Remove 0.2 mm at margin to add porcelain with chroma or translucency
• Zirconia: Solid Sintered: Moderately translucent: very high flexural and fracture toughness
• Fracture Toughness measures material’s ability to resist crack growth.
• Zirconia has the ability to get tougher by transformation of crystals through the application of mechanical energy. Crystals will heal tiny cracks by changing shape of the crystals

Cercon:

• Economical solid sintered porcelain.
• Useful for 3 unit bridge frameworks:
• It is milled in CAD CAM like Procera. It is a nonphase polycrystal

When taking impressions, place some of the light body onto the tray was well as around preparation to help blend the two. Hydrophilic material contact angle should be greater than 90 degrees.

Wettable material contact angle should be approximately 180 degrees which is much better. Therefore purchase wettable material over hydrophilic

• In order to provide a layered Empress restoration, a reduction thickness is minimum 1.0-1.2 mm which is a heavy reduction for veneers
• Empress is high fusing yet low wear
• Conventional porcelain is leucite crystals imbedded in glass matrix
• In small crystals- when leucite crystals cool there is less resultant shrinkage which helps to prevent micro cracks
• Large leucite crystals in feldspathic porcelains are very abrasive
• There is really very little difference in the composition between Empress and Feldspathic except for the size of the leucite crystals at the micro structural levels
• The term Feldspathic refers to the naturally occurring leucite crystals which are large, Empress has artificially produced leucite crystals which a much smaller therefore less abrasive
• Low fusing Porcelain is good for very thin veneers I.e.: Omega 900, dSign (850 degrees), Finesse.
• The fusing temperature must be over 800 degrees in order to remove contaminants

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