Because of its compatible thermal expansion, relatively similar cost, and cosmetic difference, some patients choose to have their crown fabricated with gold.

[4] In order to ensure optimum condition and longevity for the proposed crowns, several factors need to be explored by conducting a thorough and targeted patient history and clinical dental examination.

Despite its advantages of reducing sound tooth preparation, these crowns are not commonly prescribed in practice because they are technically difficult and have poor patient acceptability due to the metal showing through in their smile.

Generally, Type III and IV alloys (62 - 78% and 60 - 70% gold content respectively) are used in casting of full crowns, as these are hard enough to withstand occlusal forces.

Alumina (aluminium oxide) was introduced as a dental substructure (core) in 1989 when the material was slip cast, sintered, and infiltrated with glass.

During this process, particles of a slip are brought to the surface of a dental die by an electric current, thereby forming a precision-fitting core greenbody in seconds.

These crowns are produced with a core of tooth-colored tetragonal zirconia, on which a high strength translucent porcelain layer has been applied and subsequently milled to size.

As a result, the natural tooth, in terms of esthetics and hardness, is approached closer than crowns made from solid monolithic zirconia.

Zirconia is the hardest known ceramic in industry and the strongest material used in dentistry, it has to be fabricated using a CAD/CAM process but not the conventional manual dental technology.

The only thing a dental technician has to do is to use the proper height of the zirconia block so that the crown fits in all the different color zones.

However, research has shown that the shade of the supporting tooth or abutment significantly influences the final appearance of lithium disilicate crowns.

To obtain an aesthetic finish which is able to be functional with normal mastication activity, a minimal thickness of ceramic and metallic material is required, which should be planned for during tooth preparation stage.

For the crown to be retentive enough, the length of the preparation must be greater than the height formed by the arc of the cast pivoting around a point on the margin on the opposite side of the restoration.

Retention of short-walled teeth with a wide diameter can be improved by placing grooves in the axial walls, which has the effect of reducing the size of the arc.

[22] In order to last, the crown must be made of enough material to withstand normal masticatory function and should be contained within the space created by the tooth preparation, otherwise problems may arise with aesthetics and occlusal stability (i.e. high restorations) and cause periodontal inflammation.

If this functional cusp bevel is not present and the crown is cast to replicate the correct size of the tooth, bulk of material may be too little at this point to withstand occlusal surfaces.

[26][27] In dentistry, the ferrule effect is, as defined by Sorensen and Engelman (1990), a "360° metal collar of the crown surrounding the parallel walls of the dentine extending coronal to the shoulder of the preparation".

[26][27] It has been shown, however, that whilst the absence of a 360° ferrule can increase the risk of fracture of root-filled teeth restored with fiber post and cores and crowns, having insufficient coronal walls poses an even greater one.

[31] In order to accept a stainless steel crown, the entire occlusal surface should be reduced by 1–1.5 mm and interproximally contacts should be cleared by cutting a thin mesial and distal portion or slice subgingivally by holding the tip of a thin high-speed bur at 15–20° relative to the long axis of the tooth, to avoid the creation of a shoulder.

[33] The Hall technique is a non-invasive treatment for decayed posterior primary teeth where caries are sealed under a preformed stainless steel crown.

Temporisation is important after tooth preparation in order to:[36][37] Temporary crowns can also play a diagnostic role in treatment planning where there is a need for occlusal, aesthetic or periodontal changes.

[37] Zinc Oxide Eugenol (ZOE) temporary luting cements These are commonly used because of their low tensile strength and lack of adhesion which provides ease of removal.

Commercially available examples of temporary resins cements include Systemp.link (Ivoclar Vivadent), Temp-Bond Clear (Kerr) and ImProv (Nobel Biocare).

Once the tooth in question has been prepared with acceptable dimensions, it is equally important to make an accurate and dimensionally stable record or impression of the preparation or dental implant, surrounding hard and soft tissues as well as the opposing dental arch so that the restoration created will conform to the required dimensions and ensure the fit is as close as possible without having to make many modifications chair-side.

With regards to conventional impression techniques, the materials selected should have appropriate physical properties and handling characteristics to allow enough detail reproduction and durability when casting a model, including the ability to withstand effective decontamination procedures.

After selecting the proper features and making various decisions on the computerized model, the dentist directs the computer to send the information to a local milling machine.

This machine will then use its specially designed diamond burs to mill the restoration from a solid ingot of a ceramic of pre-determined shade to match the patient's tooth.

[50][53][54] In recent years, the technological advances afforded by CAD/CAM dentistry offer viable alternatives to the traditional crown restoration in many cases.

A flat plastic instrument, straight Warrick James, Couplands elevators or dedicated systems such as the WamKey, is inserted into the slot created to wedge the crown apart from the tooth.

[57] Based on the "jack-screw" principle, the Metalift system works by drilling a precision channel through the occlusal surface of a cast restoration, then with a special bur, the area around the periphery of the hole is undermined before a threaded screw is wound into the space.