Dental restoration


Dental restoration, dental fillings, or simply fillings are treatments used to restore the function, integrity, and morphology of tooth structure lost due to decay, trauma, or wear. Fillings may also be used to replace or seal tooth structure around dental implants or after more extensive procedures such as root-canal therapy. There are two broad categories of fillings: direct restorations, placed and shaped directly inside a cleaned cavity in a single dental visit, and indirect restorations, which are fabricated outside the mouth and then cemented into the tooth. Materials for direct fillings commonly include amalgam or tooth-colored composite and glass-ionomer, while indirect restorations may use ceramics, metal alloys, or porcelain for greater durability and structural support.

History

In Italy evidence dated to the Paleolithic, around 13,000 years ago, points to bitumen used to fill a tooth and in Neolithic Slovenia, 6500 years ago, beeswax was used to close a fracture in a tooth. Graeco-Roman literature, such as Pliny the Elder's Naturalis Historia, contains references to filling materials for hollow teeth.

Tooth preparation

Restoring a tooth to good form and function requires two steps:
  1. preparing the tooth for placement of restorative material or materials, and
  2. placement of these materials.
The process of preparation usually involves cutting the tooth with a rotary dental handpiece and dental burrs, a dental laser, or through air abrasion, to make space for the planned restorative materials and to remove any dental decay or portions of the tooth that are structurally unsound. If permanent restoration cannot be carried out immediately after tooth preparation, temporary restoration may be performed.
The prepared tooth, ready for placement of restorative materials, is generally called a tooth preparation. Materials used may be gold, amalgam, dental composites, glass ionomer cement, or porcelain, among others.
Preparations may be intracoronal or extracoronal. Intracoronal preparations are those which serve to hold restorative material within the confines of the structure of the crown of a tooth. Examples include all classes of cavity preparations for composite or amalgam as well as those for gold and porcelain inlays. Intracoronal preparations are also made as female recipients to receive the male components of removable partial dentures. Extracoronal preparations provide a core or base upon which restorative material will be placed to bring the tooth back into a functional and aesthetic structure. Examples include crowns and onlays, as well as veneers.
In preparing a tooth for a restoration, a number of considerations will determine the type and extent of the preparation. The most important factor to consider is decay. For the most part, the extent of the decay will define the extent of the preparation, and in turn, the subsequent method and appropriate materials for restoration.
Another consideration is unsupported tooth structure. When preparing the tooth to receive a restoration, unsupported enamel is removed to allow for a more predictable restoration. While enamel is the hardest substance in the human body, it is particularly brittle, and unsupported enamel fractures easily.
A systematic review concluded that for decayed baby teeth, putting an off‐the‐shelf metal crown over the tooth or only partially removing decay before placing a filling may be better than the conventional treatment of removing all decay before filling. For decayed adult teeth, partial removal of decay before filling the tooth, or adding a second stage to this treatment where more decay is removed after several months, may be better than conventional treatment.

Direct restorations

This technique involves placing a soft or malleable filling into the prepared tooth and building up the tooth. The material is then set hard and the tooth is restored. Where a wall of the tooth is missing and needs to be rebuilt, a matrix should be used before placing the material to recreate the shape of the tooth, so it is cleansable and to prevent the teeth from sticking together. Sectional matrices are generally preferred to circumferential matrices when placing composite restorations in that they favour the formation of a contact point. This is important to reduce patient complaints of food impaction between the teeth. However, sectional matrices can be more technique sensitive to use, so care and skill is required to prevent problems occurring in the final restoration. The advantage of direct restorations is that they are usually set quickly and can be placed in a single procedure. The dentist has a variety of different filling options to choose from. A decision is usually made based on the location and severity of the associated cavity. Since the material is required to set while in contact with the tooth, limited energy is passed to the tooth from the setting process.

Indirect restorations

In this technique the restoration is fabricated 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. The finished restoration is usually bonded permanently with a dental cement. It is often done in two separate visits to the dentist. Common indirect restorations are done using gold or ceramics.
While the indirect restoration is being prepared, a provisory/temporary restoration is sometimes used to cover the prepared tooth to help maintain the surrounding dental tissues.
Removable dental prostheses are sometimes considered a form of indirect dental restoration, as they are made to replace missing teeth. There are numerous types of precision attachments to aid removable prosthetic attachment to teeth, including magnets, clips, hooks, and implants which may themselves be seen as a form of dental restoration.
The CEREC method is a chairside CAD/CAM restorative procedure. 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. A ceramic block that matches the tooth shade is placed in the milling machine. An all-ceramic, tooth-colored restoration is finished and ready to bond in place.
Another fabrication method is to import STL and native dental CAD files into CAD/CAM software products that guide the user through the manufacturing process. The software can select the tools, machining sequences and cutting conditions optimized for particular types of materials, such as titanium and zirconium, and for particular prostheses, such as copings and bridges. In some cases, the intricate nature of some implants requires the use of 5-axis machining methods to reach every part of the job.

Cavity classifications

Greene Vardiman Black classification:
G.V. Black classified the cavities depending on their site:
  • Class I Caries affecting pit and fissure, on occlusal, buccal, and lingual surfaces of molars and premolars, and palatal of maxillary incisors.
  • Class II Caries affecting proximal surfaces of molars and premolars.
  • Class III Caries affecting proximal surfaces of centrals, laterals, and cuspids.
  • Class V Caries affecting gingival 1/3 of facial or lingual surfaces of anterior or posterior teeth.
  • Class VI Caries affecting cusp tips of molars, premolars, and cuspids.
Graham J. Mount's classification:
Mount classified cavities depending on their site and size. The proposed classification was designed to simplify the identification of lesions and to define their complexity as they enlarge.
Site:
  • Pit/Fissure: 1
  • Contact area: 2
  • Cervical: 3
Size:
  • Minimal: 1
  • Moderate: 2
  • Enlarged: 3
  • Extensive: 4

    Materials used

Alloys

The following casting alloys are mostly used for making crowns, bridges and dentures. Titanium, usually commercially pure but sometimes a 90% alloy, is used as the anchor for dental implants as it is biocompatible and can integrate into bone.
;Precious metallic alloys
  • gold
  • gold alloys
  • gold-platina alloy
  • silver-palladium alloy
;Base metallic alloys
  • cobalt-chrome alloy
  • nickel-chrome alloy

    Amalgam

Amalgams are alloys formed by a reaction between two or more metals, one of which is mercury. It is a hard restorative material and is silvery-grey in colour. One of the oldest direct restorative materials still in use, dental amalgam was widely used in the past with a high degree of success, although recently its popularity has declined due to a number of reasons, including the development of alternative bonded restorative materials, increase in demand for more aesthetic restorations and public perceptions concerning the potential health risks of the material.
The composition of dental amalgam is controlled by the ISO Standard for dental amalgam alloy. The major components of amalgam are silver, tin and copper. Other metals and small amounts of minor elements such as zinc, mercury, palladium, platinum and indium are also present. Earlier versions of dental amalgams, known as 'conventional' amalgams consisted of at least 65 wt% silver, 29 wt% tin, and less than 6 wt% copper. Improvements in the understanding of the structure of amalgam post-1986 gave rise to copper-enriched amalgam alloys, which contain between 12 wt% and 30 wt% copper and at least 40 wt% silver. The higher level of copper improved the setting reaction of amalgam, giving greater corrosion resistance and early strength after setting.
Possible indications for amalgam are for load-bearing restorations in medium to large sized cavities in posterior teeth, and in core build-ups when a definitive restoration will be an indirect cast restoration such as a crown or bridge retainer. Contraindications for amalgam are if aesthetics are paramount to patient due to the colour of the material. Amalgams should be avoided if the patient has a history of sensitivity to mercury or other amalgam components. Besides that, amalgam is avoided if there is extensive loss of tooth substance such that a retentive cavity cannot be produced, or if excessive removal of health tooth substance would be required to produce a retentive cavity.
Advantages of amalgam include durability - if placed under ideal conditions, there is evidence of good long term clinical performance of the restorations. Placement time of amalgam is shorter compared to that of composites and the restoration can be completed in a single appointment. The material is also more technique-forgiving compared to composite restorations used for that purpose. Dental amalgam is also radiopaque which is beneficial for differentiating the material between tooth tissues on radiographs for diagnosing secondary caries. The cost of the restoration is typically cheaper than composite restorations.
Disadvantages of amalgam include poor aesthetic qualities due to its colour. Amalgam does not bond to tooth easily, hence it relies on mechanical forms of retention. Examples of this are undercuts, slots/grooves or root canal posts. In some cases this may necessitate excessive amounts of healthy tooth structure to be removed. Hence, alternative resin-based or glass-ionomer cement-based materials are used instead for smaller restorations including pit and small fissure caries. There is also a risk of marginal breakdown in the restorations. This could be due to corrosion which may result in "creep" and "ditching" of the restoration. Creep can be defined as the slow internal stressing and deformation of amalgam under stress. This effect is reduced by incorporating copper into amalgam alloys. Some patients may experience local sensitivity reactions to amalgam.
Although the mercury in cured amalgam is not available as free mercury, concern of its toxicity has existed since the invention of amalgam as a dental material. It is banned or restricted in Norway, Sweden and Finland. See dental amalgam controversy.