Onlays are a type of filling, originally developed at a time when conventional filling materials were not strong enough to withstand the forces placed on them in cases where there was little of the original tooth tissue left and insufficient tooth tissue for the provision of a crown.

They went out of fashion with the arrival of modern dental materials but have seen a return to popularity with modern porcelains and zirconia. They are stronger than materials pressed into the tooth directly and are used when other filling materials fracture. Onlays are custom made for each tooth they are placed on.

No two onlays are the same. They are normally cast or milled to the specific shape required at a dental laboratory. Typically, there are two stages to the fabrication of an onlay. The first stage is to prepare the tooth for the onlay, which will involve the numbing and removing of tooth tissue and any decay present. An impression of the tooth is then taken and a temporary filler is placed.

The second stage takes place a week later and involves numbing the tooth to remove the temporary filling, then checking the fit and colour of the new onlay before finally cementing it in place.

The onlay is stronger than any filling material however, it will never be as robust as a healthy tooth. The strength of the onlay comes from the strength of the underlying tooth tissue and, as this has been compromised, its longevity is never as good as a natural, healthy tooth.

Onlays come in a range of materials, gold, porcelain and zirconia. Your dentist is the best person to discuss the suitability of each material.

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