Dental filling

# Overview
A dental restoration or dental filling is a dental restorative material used artificially 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 by restoring 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. If decay is spread beyond dentin, in that case root canal therapy is used, and a crown is fit.

# Tooth preparation
Tooth preparation is cutting infected tooth cavity to clean and finish it for filling. Generally a dental drill is used for the purpose. If permanent restoration can not be carried out after tooth preparation, temporary restoration is done.

# Direct restorations
Direct restorations are placed in the tooth in situ, while indirect restorations are created away from the tooth, traditionally prepared in a laboratory. Direct restorations are done using materials amalgam(silver color) or dental composite(white color) or suitable restorative materials. If filled by white composite, the filling is photo-polymerised using a blue spectrum light, not to be confused with UV light, and maybe polished also. It is recommended not to chew anything hard for a day or two after fillings, which may dislodge fillings.

# Indirect restorations
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. Once a proper fit and bite is confirmed the restoration is usually bonded permanently.
While the indirect restoration is being prepared, a provisory/temporary restoration sometimes is used to cover the prepared part of the tooth, in order to maintain the occlusal space and the contact points, and insulation of the pulpal tissues and maintenance of the periodontal relationship.
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.

# Restoration by dental implants
Dental implants are becoming more widely used as the technology and treatment research improves. A dental implant, usually  made from titanium or titanium alloy, is a screw which anchors into maxillary or mandibular bone. Some of the uses of dental implants in restorative care are to support an implant crown, bridge, or dental prosthesis. Ideally the bone integrates into the implant screw's roughened surface.

# Restoration classifications
G V Black classified the fillings depending on their size and location.
For example, a one surface filling is called "Class I" under Black's system.
GV Black Classification of Restorations

# Materials used in dental restorations

## 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.
- titanium

### Precious metallic alloys
- gold (high purity: 99.7%)
- gold alloys (with high gold content)
- gold-platina alloy
- silver-palladium alloy

### Base metallic alloys
- cobalt-chromium alloy
- nickel-chrome alloy

### Amalgam
- Amalgam

## 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.

### 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, do not support the use of conventional or metal-reinforced glass ionomer restorations in primary molars.

### 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.

## 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 producability 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.

# 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 is 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.