A crown (or cap) is a shell that fits over a tooth, giving it strength and/or improving its appearance. The tooth has to be reduced in size to make room for the crown. Crowns may be made from precious or non-precious metals, tooth coloured materials (ceramics and resin-based composites) or a combination of both.

Indications For Crowns

Crowns are indicated for teeth which are too extensively decayed, damaged or discoloured for treatment by other means Metal crowns are indicated for back teeth where strength is important but appearance is not a factor. Tooth-coloured crowns (ceramic and composite) are indicated for front teeth where good appearance is desired, and metal backed ceramic crowns are indicated where strength, wear resistance and aesthetics are critical.

Before a crown is provided

Complicated cases may require photographs, and/or laboratory mock-ups of the intended final tooth shapes and perhaps even computer imaging if this is available to the dentist. The choice is based on the individual clinical situation and the dentist may offer more than one option.

After examining your mouth and taking a history the dentist may need to undertake further investigations and perform special tests before he/she can suggest appropriate treatment option(s). These may include taking impressions to assess tooth relationships (the occlusion), checking the reaction to sensation of the teeth (are the nerves alive?) and taking x-rays. The shade has also to be recorded when it is intended to make the crown out of a tooth-coloured material.

Preparing a tooth for a crown

The tooth/teeth may require root filling or rebuilding with a "build-up core" material before the dentist drills the tooth to a "peg" shape for the crown.

Tooth preparation is normally done under a local anaesthetic and takes approximately 15 minutes per tooth. The dentist then takes an impression of the prepared tooth/teeth with a silicone putty material which hardens in 3 to 5 minutes. A temporary crown (made out of plastic or aluminium) is used to maintain the appearance, and keep the tooth comfortable and in the correct position, whilst the crown is being made in the laboratory.

A few dentists possess CAD-CAM (computer aided design and manufacturing) machines in their surgeries. These allow the cap to be made at the same sitting and do away with the need for impressions, temporary caps and a second visit.

Fitting the crown

The quality of the final crown depends both on the skill of the dentist and the technician, and this accounts for the relatively high fee scales for these items. At the fitting visit (usually 1 - 2 weeks later), the temporary is removed and the crown tried in to assess that it has an adequate appearance, fit, shape, and the occlusion is correct. Adjustments are made if required and the crown is finally cemented with a dental cement. Retention may depend solely on the mechanical interlocking effect of the cement to the appropriately shaped tooth stump or an adhesive treatment coupled with a resin based cement may be employed in some cases.

After the cement has set, excess is removed and the occlusion re-checked. Recall appointments are required to evaluate comfort and effectiveness of the patient's dental hygiene.

How long a crown lasts

A well made crown made in a situation where the overall dental outlook is favourable (low and stable decay rate, healthy gums and good oral hygiene, no excessive tooth wear or tooth clenching/grinding habits and no history of patient involvement in contact sports) should last for 10 to 20 years.

Follow-up radiographs may be indicated as the nerve in a small percentage of teeth dies after crown work

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