Dental porcelain

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Bridge from dental porcelain.jpg

Dental porcelain (also known as dental ceramic) is a dental material used by dental technicians to create biocompatible lifelike dental restorations, such as crowns, bridges, and veneers. Evidence suggests they are an effective material as they are biocompatible, aesthetic, insoluble and have a hardness of 7 on the Mohs scale. For certain dental prostheses, such as three-unit molars porcelain fused to metal or in complete porcelain group, zirconia-based restorations are recommended. [1]

Contents

The word "ceramic" is derived from the Greek word κέραμος keramos, meaning "potter's clay". [2] It came from the ancient art of fabricating pottery where mostly clay was fired to form a hard, brittle object; a more modern definition is a material that contains metallic and non-metallic elements (usually oxygen). These materials can be defined by their inherent properties including their hard, stiff, and brittle nature due to the structure of their inter-atomic bonding, which is both ionic and covalent. In contrast, metals are non-brittle (display elastic behavior), and ductile (display plastic behaviour) due to the nature of their inter-atomic metallic bond. These bonds are defined by a cloud of shared electrons with the ability to move easily when energy is applied. Ceramics can vary in opacity from very translucent to very opaque. In general, the more glassy the microstructure (i.e. noncrystalline) the more translucent it will appear, and the more crystalline, the more opaque. [3]

Composition

Ceramic used in dental application differs in composition from conventional ceramic to achieve optimum aesthetic components such as translucency.

As example the composition of dental feldspathic porcelain is as follows: [4]

Classification

Ceramics can be classified based on the following: [3] [5]

Feldspathic porcelain fabricated on a dental model, then clinically cemented on the central anterior teeth Feldspathic VM9 Porcelain Crowns -side view.jpg
Feldspathic porcelain fabricated on a dental model, then clinically cemented on the central anterior teeth

Classification by Microstructure

At the microstructural level, ceramics can be defined by the nature of their composition of amorphous-to-crystalline ratio. There can be an infinite variability of the microstructures of materials, but they can be broken down into four basic compositional categories, with a few subgroups:

Dental ceramic is generally regarded as biologically inert. However, other toxicities may exist from depleted uranium as well as some of the other accessory materials; in addition, the restoration may increase wear on opposing teeth. [6]

Classification by Processing Technique

Classification of crystalline ceramics

Classification of crystalline ceramics [5]
Fabrication techniqueCrystalline phase
Metal-ceramicsSinteringLeucite
Heat-pressing on metalLeucite, leucite & fluorapatite
All-ceramicsSinteringLeucite
Heat-pressingLeucite, lithium disilicate
Dry pressing and sinteringAlumina
Slip-casting & glass infiltrationAlumina, spinel, alumina-zirconia (12Ce-TZP)
Soft machining & glass-infiltrationAlumina, alumina-zirconia (12Ce-TZP)
Soft machining & sinteringAlumina, zirconia (3Y-TZP)
Soft machining, sintering & heat-pressingZirconia/fluorapatite-leucite glass-ceramic
Hard machiningSanidine, leucite
Hard machining & heat treatmentLithium disilicate

Types of dental ceramics

The range of dental ceramics determined by their respective firing temperatures are:

Fired below 850 °C - mainly used for shoulder ceramics (aims to combat the problem of shrinkage, specifically at the margins of the prep, when the early sintered ceramic state is fired to produce the final restoration), to correct minor defects and to add colour/shading to restorations

Fired between 850 and 950 °C - to prevent the occurrence of distortion, this type of ceramic should not be subjected to multiple firings

This type is used mainly for denture teeth

Laboratory procedure

The dentist will usually specify a shade or combination of shades for different parts of the restoration, which in turn corresponds to a set of samples containing the porcelain powder. There are two types of porcelain restorations: [9]

Ceramic restorations can be built on a refractory die, which is a reproduction of a prepared tooth made of a strong material with the ability to withstand high temperatures, or it can be constructed on a metal coping or core.

For ceramic fused to metal restorations, the black color of metal is first masked with an opaque layer giving it a shade of white before consecutive layers are built up. The powder corresponding to the desired shade of dentine base is mixed with water before it is fired. Further layers are built up to mimic the natural translucency of the enamel of the tooth. The porcelain is fused to a semi-precious metal or precious metal, such as gold, for extra strength.

Systems which use an aluminium oxide, zirconium oxide or zirconia core instead of metal, produces complete porcelain restorations. [10]

Firing

Once the mass has been built up, it is fired to allow fusion of the ceramic particles which in turn forms the completed restoration; the process by which this is done is referred to as ‘firing’. [4]

The first firing forces water out and allows the particles to coalesce. During this initial process, a large amount of shrinkage occurs until the mass reaches an almost void-free state; to overcome this the mass is built-up to a size larger than the final restoration will be.

The mass is then left to cool slowly to prevent cracking and reduced strength of the final restoration.

Adding more layers to build up the restoration to the desired shape and/or size requires the ceramic to undergo further rounds of firing.

Staining

Ceramic can also be stained to show tooth morphology such as occlusal fissures and hypoplastic spots. These stains can be incorporated within the ceramic or applied onto the surface. [4]

Glazing

Glazing is required to produce a smooth surface and it's the last stage of sealing the surface as it will fill porous areas and prevent wear on opposing teeth. Glazing can be achieved by re-firing the restoration, which fuses outer layers of the ceramic, or by using glazes with lower fusing temperatures; these are applied on the outer surface of the restoration in a thin layer. Any adjustments are then made with polishing rubbers and fine diamonds. [4]

Use of CAD-CAM

Recent developments in CAD/CAM dentistry uses special partially sintered ceramic (zirconia), glass-bonded ceramic or glass-ceramic (lithium disilicate) [11] formed into machinable blocks, which are fired again after machining. [12] [8]

By utilising in-office CAD/CAM technology, clinicians are able to design, fabricate and place all-ceramic inlays, onlays, crowns and veneers in a single patient visit. Ceramic restorations produced by this method have demonstrated excellent fit, strength and longevity. Two basic techniques can be used for CAD/CAM restorations:

Ceramic restorations

Ceramic restorations are indicated for most dental applications including: [4]

However, each system will have its own set of specific indications and contraindications which can be obtained from the manufacturers guideline.

Contraindications for ceramic restorations

Ceramic restorations are contraindicated when a patient presents with the following: [4]

Other uses

Denture teeth

Poly(methyl methacrylate) (PMMA) is the material of choice for denture teeth, however ceramic denture teeth have been, and still are used for this purpose. The main benefit associated with the use of ceramic teeth is their superior wear resistance. There are however a number of disadvantages to using ceramic for denture teeth including their inability to form chemical bonds with the PMMA denture base; rather, ceramic teeth are attached to the base via mechanical retention which increases the chance of debonding during use over time. Additionally, they are more likely to fracture due to their brittle nature. [4]

Endodontic posts

Ceramic can be used in the construction of non-metallic posts, however, it is a brittle material and as such may fracture within the root canal or may cause fracture of the root due to its increased strength. Another disadvantage is that once placed, removal may not be possible. [4]

Related Research Articles

<span class="mw-page-title-main">Ceramic</span> Inorganic, nonmetallic solid prepared by the action of heat

A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, and brick.

<span class="mw-page-title-main">Zirconium dioxide</span> Chemical compound

Zirconium dioxide, sometimes known as zirconia, is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabilized cubic structured zirconia, cubic zirconia, is synthesized in various colours for use as a gemstone and a diamond simulant.

Dental products are specially fabricated materials, designed for use in dentistry. There are many different types of dental products, and their characteristics vary according to their intended purpose.

<span class="mw-page-title-main">Bridge (dentistry)</span> Dental restoration for missing teeth

A bridge is a fixed dental restoration used to replace one or more missing teeth by joining an artificial tooth definitively to adjacent teeth or dental implants.

Dental restoration, dental fillings, or simply fillings are treatments used to restore the function, integrity, and morphology of missing tooth structure resulting from caries or external trauma as well as to the replacement of such structure supported by dental implants. They are of two broad types—direct and indirect—and are further classified by location and size. A root canal filling, for example, is a restorative technique used to fill the space where the dental pulp normally resides.

<span class="mw-page-title-main">Crown (dental restoration)</span> Dental prosthetic that recreates the visible portion of a tooth

In dentistry, a crown or a dental cap is a type of dental restoration that completely caps or encircles a tooth or dental implant. A crown may be needed when a large dental cavity threatens the health of a tooth. Some dentists will also finish root canal treatment by covering the exposed tooth with a crown. A crown is typically bonded to the tooth by dental cement. They can be made from various materials, which are usually fabricated using indirect methods. Crowns are used to improve the strength or appearance of teeth and to halt deterioration. While beneficial to dental health, the procedure and materials can be costly.

<span class="mw-page-title-main">Inlays and onlays</span> Restoration procedure in dentistry

In dentistry, inlays and onlays are used to fill cavities, and then cemented in place in the tooth. This is an alternative to a direct restoration, made out of composite, amalgam or glass ionomer, that is built up within the mouth.

<span class="mw-page-title-main">Yttrium(III) oxide</span> Chemical compound

Yttrium oxide, also known as yttria, is Y2O3. It is an air-stable, white solid substance.

<span class="mw-page-title-main">Veneer (dentistry)</span> Layer of material placed over a tooth

In dentistry, a veneer is a layer of material placed over a tooth. Veneers can improve the aesthetics and function of a smile and protect the tooth's surface from damage.

<span class="mw-page-title-main">Ceramic engineering</span> Science and technology of creating objects from inorganic, non-metallic materials

Ceramic engineering is the science and technology of creating objects from inorganic, non-metallic materials. This is done either by the action of heat, or at lower temperatures using precipitation reactions from high-purity chemical solutions. The term includes the purification of raw materials, the study and production of the chemical compounds concerned, their formation into components and the study of their structure, composition and properties.

<span class="mw-page-title-main">Luting agent</span>

A luting agent is a dental cement connecting the underlying tooth structure to a fixed prosthesis. To lute means to glue two different structures together. There are two major purposes of luting agents in dentistry – to secure a cast restoration in fixed prosthodontics, and to keep orthodontic bands and appliances in situ.

<span class="mw-page-title-main">CAD/CAM dentistry</span> Computer-aided design and manufacturing of dental prostheses

CAD/CAM dentistry is a field of dentistry and prosthodontics using CAD/CAM to improve the design and creation of dental restorations, especially dental prostheses, including crowns, crown lays, veneers, inlays and onlays, fixed dental prostheses (bridges), dental implant supported restorations, dentures, and orthodontic appliances. CAD/CAM technology allows the delivery of a well-fitting, aesthetic, and a durable prostheses for the patient. CAD/CAM complements earlier technologies used for these purposes by any combination of increasing the speed of design and creation; increasing the convenience or simplicity of the design, creation, and insertion processes; and making possible restorations and appliances that otherwise would have been infeasible. Other goals include reducing unit cost and making affordable restorations and appliances that otherwise would have been prohibitively expensive. However, to date, chairside CAD/CAM often involves extra time on the part of the dentist, and the fee is often at least two times higher than for conventional restorative treatments using lab services.

A post and core crown is a type of dental restoration required where there is an inadequate amount of sound tooth tissue remaining to retain a conventional crown. A post is cemented into a prepared root canal, which retains a core restoration, which retains the final crown.

Adhesive dentistry is a branch of dentistry which deals with adhesion or bonding to the natural substance of teeth, enamel and dentin. It studies the nature and strength of adhesion to dental hard tissues, properties of adhesive materials, causes and mechanisms of failure of the bonds, clinical techniques for bonding and newer applications for bonding such as bonding to the soft tissue. There is also direct composite bonding which uses tooth-colored direct dental composites to repair various tooth damages such as cracks or gaps.

A resin-retained bridge is a bridge replacing a missing tooth that relies for its retention on a composite resin cement. It is one of many available dental restoration methods which is considered minimally invasive and conservative of tooth tissue. The resin-retained-bridge has gone through a number of iterations. Perhaps the best known is the Maryland bridge and other designs used in the past include the Rochette bridge. The five-year survival rate is around 83.6% and the ten-year rate at 64.9%. The case selection is important and as with any dental prosthesis, good oral hygiene is paramount for success. In recent years, the indications for the use of resin-retained-bridges have diminished significantly and there have been changes in the principles underpinning their design. Resin-retained-bridges should be considered when a fixed prosthesis retained by natural teeth is required. The use has been driven by the advent of evidence-based dentistry showing the benefits to patients of reduced tooth preparation and the importance of an intact enamel structure for the long-term health of the teeth. The bridge is currently in favour in the United Kingdom for these reasons. Indeed, recent contemporary research shows resin retained bridges have better success rates than implants and are a cheaper alternative.

<span class="mw-page-title-main">Solid</span> State of matter

Solid is one of the four fundamental states of matter along with liquid, gas, and plasma. The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural rigidity and resistance to a force applied to the surface. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire available volume like a gas. The atoms in a solid are bound to each other, either in a regular geometric lattice, or irregularly. Solids cannot be compressed with little pressure whereas gases can be compressed with little pressure because the molecules in a gas are loosely packed.

<span class="mw-page-title-main">Bioceramic</span> Type of ceramic materials that are biocompatible

Bioceramics and bioglasses are ceramic materials that are biocompatible. Bioceramics are an important subset of biomaterials. Bioceramics range in biocompatibility from the ceramic oxides, which are inert in the body, to the other extreme of resorbable materials, which are eventually replaced by the body after they have assisted repair. Bioceramics are used in many types of medical procedures. Bioceramics are typically used as rigid materials in surgical implants, though some bioceramics are flexible. The ceramic materials used are not the same as porcelain type ceramic materials. Rather, bioceramics are closely related to either the body's own materials or are extremely durable metal oxides.

Pediatric crowns are dental crowns used for restoring lost or damaged or decayed teeth of children. These crowns encircle the damaged teeth completely and are made of different materials such as ceramic, steel and more.

The history of dental treatments dates back to thousands of years. The scope of this article is limited to the pre-1981 history.

Lithium disilicate (Li2Si2O5) is a chemical compound that is a glass ceramic. It is widely used as a dental ceramic due to its strength, machinability and translucency.

References

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