Inlays and onlays

In dentistry, inlays and onlays are a form of indirect restoration. This means they are made outside of the mouth as a single, solid piece, that fits the specific size and shape of the cavity. The restoration is then cemented in place in the mouth. This is an alternative to a direct restoration, made out of composite, amalgam or glass ionomer, that is built up within the mouth. In dentistry, inlays and onlays are a form of indirect restoration. This means they are made outside of the mouth as a single, solid piece, that fits the specific size and shape of the cavity. The restoration is then cemented in place in the mouth. This is an alternative to a direct restoration, made out of composite, amalgam or glass ionomer, that is built up within the mouth. Inlays and onlays are used in molars or premolars, when the tooth has experienced too much damage to support a basic filling, but not so much damage that a crown is necessary. The key comparison between them is the amount and part of the tooth that they cover. An inlay will incorporate the pits and fissures of a tooth, mainly encompassing the chewing surface between the cusps. An onlay will involve one or more cusps being covered. If all cusps and the entire surface of the tooth is covered this is then known as a crown. Historically inlays and onlays will have been made from gold and this material is still commonly used today. Alternative materials such as porcelain were first described being used for inlays back in 1857. Due to its tooth like colour, porcelain provides better aesthetic value for the patient. In more recent years, inlays and onlays have increasingly been made out of ceramic materials. In 1985, the first ceramic inlay created by a chair-side CAD-CAM device was used for a patient. More recently, in 2000, the CEREC 3® was introduced. This allows for inlays and onlays to be created and fitted all within one appointment. Furthermore, no impression taking is needed due to the 3D scanning capabilities of the machine. Sometimes, a tooth is planned to be restored with an intracoronal restoration, but the decay or fracture is so extensive that a direct restoration, such as amalgam or composite, would compromise the structural integrity of the restored tooth or provide substandard opposition to occlusal (i.e., biting) forces. In such situations, an indirect gold or porcelain inlay restoration may be indicated. When an inlay is used, the tooth-to-restoration margin may be finished and polished to a very fine line of contact to minimize recurrent decay. Opposed to this, direct composite filling pastes shrink a few percent in volume during hardening. This can lead to shrinkage stress and rarely to marginal gaps and failure. Although improvements of the composite resins could be achieved in the last years, solid inlays do exclude this problem. Another advantage of inlays over direct fillings is that there is almost no limitations in the choice of material.While inlays might be ten times the price of direct restorations, it is often expected that inlays are superior in terms of resistance to occlusal forces, protection against recurrent decay, precision of fabrication, marginal integrity, proper contouring for gingival (tissue) health, and ease of cleansing offers. However, this might be only the case for gold. While short term studies come to inconsistent conclusions, a respectable number of long-term studies detect no significantly lower failure rates of ceramicor compositeinlays compared to composite direct fillings. Another study detected an increased survival time of composite resin inlays but it was rated to not necessarily justify their bigger effort and price. When decay or fracture incorporate areas of a tooth that make amalgam or composite restorations inadequate, such as cuspal fracture or remaining tooth structure that undermines perimeter walls of a tooth, an onlay might be indicated. Similar to an inlay, an onlay is an indirect restoration which incorporates a cusp or cusps by covering or onlaying the missing cusps. All of the benefits of an inlay are present in the onlay restoration. The onlay allows for conservation of tooth structure when the only alternative is to totally eliminate cusps and perimeter walls for restoration with a crown. Just as inlays, onlays are fabricated outside of the mouth and are typically made out of gold or porcelain. Gold restorations have been around for many years and have an excellent track record. In recent years, newer types of porcelains have been developed that seem to rival the longevity of gold. If the onlay or inlay is made in a dental laboratory, a temporary is fabricated while the restoration is custom-made for the patient. A return visit is then required to fit the final prosthesis. Inlays and onlays may also be fabricated out of porcelain and delivered the same day utilizing techniques and technologies relating to CAD/CAM dentistry. A systemic review found that the most common cause of onlay failure is ceramic fracture, followed by ceramic de-bonding from the tooth structure, and the occurrence of secondary caries which is seen as a discolouration at the margins of the restoration. High failure rates were associated with teeth that had previous root canal treatment, and with patients who exhibit para-functional habits such as bruxism , or teeth clenching.