Inlays / Onlays

The difference between inlays and onlays (or indirect fillings) and composite or tooth-coloured fillings is that they are made in a dental laboratory. Unlike composite fillings which can be fitted during a single dental appointment, indirect fillings require two visits – the first to fit a temporary filling while the indirect filling is being prepared in the laboratory, the second to fit the replacement. This technique is employed when the tooth structure has become too damaged to support a filling (although not enough to warrant a crown).

The initial visit will involve the removal of the decayed matter or any original filling material. The dentist will then take an impression of the tooth requiring repair, as well as surrounding teeth. This impression will be sent to the dental laboratory. The dentist will then fit a temporary filling to protect the damaged tissue. At the subsequent visit, this temporary filling will be removed. The dentist will ensure that the indirect filling received from the laboratory fits the area perfectly. Finally, this filling will be cemented into position.

Properties of inlays and onlays

Inlays are indirect fillings where the entire work lies within the cusps (or bumps) that lie on the tooth’s chewing surface. Onlays (otherwise known as partial crowns) are more extensive, covering one or more cusps.

Indirect fillings last longer than traditional fillings – anything up to 30 years. They can be manufactured from a variety of substances, from tooth-coloured composite resin to gold. Although they do weaken tooth structure, they do this to a far lesser extent than other types of filling.

An alternative form of inlays and outlays are the direct variety. While these follow the same procedure as indirect fillings, they are made in the dental surgery rather than the laboratory, meaning only a singular visit is required. The dentist will decide on which type of indirect filling to use depending on the extent of damage to the tooth structure, and whether or not there are cosmetic concerns.