Dental restoration:
A dental restoration or dental filling is a dental restorative material used to restore the function, integrity and morphology of missing tooth structure. The structural loss typically results from caries or external trauma. It is also lost intentionally during tooth preparation to improve the aesthetics or the physical integrity of the intended restorative material. Dental restoration also refers to the replacement of missing tooth structure which is supported by dental implants.
Dental restorations may be fabricated out of a variety of materials, Common direct restorative materials include dental amalgam, glass ionomer cement and composite resins. Common indirect restorative materials include acrylic, porcelain, zirconia, gold and other metals.
Dental restorations can be divided into two broad types: direct restorations and indirect restorations. All dental restorations can be further classified by their location and size. A root canal filling is a restorative technique used to fill the space where the dental pulp normally resides.
[edit] Tooth preparation
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Tooth preparation is usually required before placing a dental restoration. This process involves cutting the tooth usually with a dental drill to make space for the planned restoration, remove any dental decay and structurally unsound tooth. If permanent restoration can not be carried out after tooth preparation, temporary restoration is done.
[edit] Direct restorations
This technique involves placing a soft or malleable filling into the prepared tooth and building up the tooth before the material sets hard. The advantage of direct restorations is that they usually set quickly and can be placed by one operator. Since the material is required to set while in contact with the tooth, limited energy can be passed to the tooth from the setting process without damaging it. Where strength is required especially as the fillings become larger indirect restorations may be the best choice.
[edit] Indirect restorations
This technique of fabricating the restoration outside of the mouth using the dental impressions of the prepared tooth. Common indirect restorations include inlays and onlays, crowns, bridges, and veneers.
Usually a dental technician fabricates the indirect restoration from records the dentist has provided of the prepared tooth. The finished restoration is usually bonded permanently with a dental cement.
While the indirect restoration is being prepared, a provisory/temporary restoration sometimes is used to cover the prepared part of the tooth, which can help maintain the surrounding dental tissues.
Removable dental prostheses (mainly dentures) are considered by some to be a form of indirect dental restoration, as they are made to replace missing teeth. There are numerous types of precision attachments (also known as combined restorations) to aid removable prosthetic attachment to teeth, including magnets, clips, hooks and implants which could be seen as a form of dental restoration.
[edit] Restoration of dental implants
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Main article: Dental implant
Dental implants, are anchors placed in bone, usually made from titanium or titanium alloy. They can support dental restorations which replace missing teeth. Some restorative applications include supporting crowns, bridges, or dental prostheses.
[edit] Restoration classifications
Greene Vardiman Black classified the fillings depending on their size and location. For example, a one surface filling is called "Class I" under Black's system.[1]
GV Black Classification of Restorations
[edit] Materials used in dental restorations
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[edit] Metals (and metallic alloys)
These metals are mostly used for making crowns, bridges and dentures. Pure titanium could be successfully incorporated into bone. It is biocompatible and stable.
[edit] Precious metallic alloys
- gold (high purity: 99.7%)
- gold alloys (with high gold content)
- gold-platina alloy
- silver-palladium alloy
[edit] Base metallic alloys
[edit] Amalgam
[edit] Dental composites
Dental composites are also called white fillings, used in direct fillings. Crowns and in-lays can also be made in the laboratory from dental composites. These materials are similar to those used in direct fillings and are tooth coloured. Their strength and durability is not as high as porcelain or metal restorations and they are more prone to wear and discolouration.
[edit] Glass ionomer cement
A glass ionomer cement (GIC) is one of a class of materials commonly used in dentistry as filling materials and luting cements. These materials are based on the reaction of silicate glass powder and polyalkeonic acid. These tooth-coloured materials were introduced in 1972 for use as restorative materials for anterior teeth (particularly for eroded areas, Class III and V cavities).
As they bond chemically to dental hard tissues and release fluoride for a relatively long period modern day applications of GICs have expanded. The desirable properties of glass ionomer cements make them useful materials in the restoration of carious lesions in low-stress areas such as smooth-surface and small anterior proximal cavities in primary teeth. Results from clinical studies also support the use of conventional glass ionomer restorations in primary molars.
[edit] Composite resin
Dental composites, also called white fillings, are a group of restorative materials used in dentistry. As with other composite materials, a dental composite typically consists of a resin-based matrix, such as a bisphenol A-glycidyl methacrylate BISMA resin like urethane dimethacrylate (UDMA), and an inorganic filler such as silicon dioxide silica. Compositions vary widely, with proprietary mixes of resins forming the matrix, as well as engineered filler glasses and glass ceramics. The filler gives the composite wear resistance and translucency. A coupling agent such as silane is used to enhance the bond between these two components. An initiator package begins the polymerization reaction of the resins when external energy (light/heat etc.) is applied. A catalyst package can control its speed.
[edit] Porcelain (ceramics)
Full-porcelain (ceramic) dental materials include porcelain, ceramic or glasslike fillings and crowns (a.k.a jacket crown, as a metal free option). They are used as in-lays, on-lays, crowns and aesthetic veneers. A veneer is a very thin shell of porcelain that can replace or cover part of the enamel of the tooth. Full-porcelain (ceramic) restorations are particularly desirable because their color and translucency mimic natural tooth enamel.
Another type is known as porcelain-fused-to-metal, which is used to provide strength to a crown or bridge. These restorations are very strong, durable and resistant to wear, because the combination of porcelain and metal creates a stronger restoration than porcelain used alone.
One of the blessings of computerized dentistry (CAD/CAM technologies) is that it enabled the application of zirconium-oxide (ZrO2). The introduction of this material in restorative and prosthetic dentistry is most likely the decisive step towards the use of full ceramics without limitation. With the exception of zirconium-oxide, existing ceramics systems lack reliable potential for the various indications for bridges without size limitations. Zirconium-oxide with its high strength and comparatively higher fracture toughness seems to buck this trend. With a three-point bending strength exceeding nine hundred megapascals, zirconium-oxide can be used in virtually every full ceramic prosthetic solution, including bridges, implant supra structures and root dowel pins.
Previous attempts to extend its application to dentistry were thwarted by the fact that this material could not be processed using traditional methods used in dentistry. The arrival of computerized dentistry enables the economically prudent use of zirconium-oxide in such elements as base structures such as copings and bridges and implant supra structures. Special requirements apply to dental materials implanted for longer than a period of thirty days. Several technical requirements include high strength, corrosion resistance and defect-free producibility at a reasonable price.
Ever more stringent requirements are being placed on the aesthetics of teeth. Metals and porcelain are currently the materials of choice for crowns and bridges. The demand for full ceramic solutions, however, continues to grow. Consequently, industry and science are increasingly compelled to develop full ceramic systems. In introducing full ceramic restorations, such as base structures made of sintered ceramics, computerized dentistry plays a key role.
[edit] Discomfort/Causes
In modern dentistry, the material most commonly used to fill decaying teeth is known as dental amalgam, or a substance made by combining mercury with another metal. The amalgam consists of three solid phases having stoichiometries approximately corresponding to Ag2Hg3, Ag3Sn, and Sn8Hg. Anyone who bites a piece of aluminium foil in such a way that the foil presses against a dental filling will probably experience a momentary pain. In effect, an electrochemical cell has been created, with aluminium (E0 = -1.66 V) as the anode and the saliva and filling as the electrolyte. Contact between the aluminium and the filling short circuits the cell, causing a weak currect to flow between the electrodes. This thus stimulates the sensitive nerve within the tooth, causing an unpleasant sensation.
In addition, discomfort results when a less electro-positive metal touches a dental filling. For example, if a filling makes contact with a gold inlay in a nearby tooth, corrosion of the filling will occur. Here, the dental filling acts as the anode, and the gold inlay acts as the cathode. As the Sn8Hg phase is the most likely to corrode, the release of the Sn (II) ions in the mouth produces the unpleasant metallic taste that we often feel. Prolonged corrosion will eventually result in another visit to the dentist for another replacement.[2]
Sometimes a cavity can be very deep and close to the nerve. When this happens, the dentist will put a medicated temporary filling in the tooth for a while before putting in the permanent filling. This significantly reduces the chances of sensitivity especially to hot and cold.
[edit] Dental restorations made by using computer technology (CAD/CAM)
The CEREC method is a chairside CAD/CAM restorative procedure. The dentist examines the tooth and determines the appropriate treatment. It could be a simple filling, an in-lay or a full crown, depending on how much healthy tooth structure is remaining. Then an optical impression of the prepared tooth is taken using a camera. Next, the specific software takes the digital picture and converts it into a 3D virtual model on the computer screen. After that, the restoration design data are sent to a separate milling machine in the office. A ceramic block that matches the tooth shade is placed in the milling machine. About 10–20 minutes later, an all-ceramic, tooth-colored restoration is finished and ready to bond in place.
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