May 08, 2016
Inlay, onlay, overlay and pinlay are types of restorative prosthesis that fall somewhere between fillings and dental crowns. In other words, these microdentures are used to restore cavities that are too large for fillings but can be managed without installing crowns. This is a conservative treatment and is preferred over crowns as they help to preserve more of the natural tooth structure.
They are now primarily used for the back teeth like premolars and molars. Utilized to strengthen damaged teeth, they facilitate chewing and prevent further decay. Earlier they were also used for front teeth, but veneers are now the preferred option for anterior restorations due to esthetic concerns.
Also known as indirect fillings, they can be made of different materials like, composite, porcelain and gold. Unlike fillings they require two sittings with the dentist. In the first appointment the dentist prepares the tooth and takes an impression to send to the dental laboratory. The restoration is fabricated in the lab and installed by the dentist in the second sitting. Meanwhile a temporary filling is placed in the cavity to protect the tooth.
Some dentists who have the necessary equipment are able to fabricate inlays, onlays and overlays, within their practice and are able to complete the procedure in one go. This is with the help of a computerized system and milling machine that can create ceramic inlays and onlays. In this system a scanning device is used instead of impression cast model. This digital image is then used by the milling machine to create a ceramic inlay from a block of ceramic.
What is the difference between inlays, onlays, overlays and pinlays?
These are all indirect fillings and are named according to the part of the tooth structure being repaired. There are four types - inlays, onlays and overlays, pinlays, and all of them replace different parts of the hard tissue structure in varying degrees. When the dentist selects either of these restorative fillings, he takes into consideration, not only the extent of the cavity but also the condition of the natural tooth walls, any micro cracks, chipping of the enamel as well as the condition of the dental pulp and the opposing teeth.
The main difference among inlays, onlays and overlays is in the size of damage and the area of the tooth being treated. Inlays cover the central part of the tooth and are positioned within the hard tissues of the tooth. They do not cover the cusps or the pointed parts of the tooth. On the other hand onlays cover a larger area. Besides replacing the internal part of the damaged tooth, they also cover one of the cusps. So, they are positioned inside the deep tissues of the tooth as well as cover part of the biting surface of the tooth. This helps to protect the damaged tooth from direct chewing load.
In cases where there is a large area between the cusps that is being covered by inlays, there are chances that it may force the cusps apart under chewing pressure. This increases the risk of tooth fracture in the future. Onlays or overlays which spread chewing pressure uniformly and also cover one or more cusps reduce the possibility of fractures.
Overlays cover a much larger portion of the occlusal or biting surface. Though, they are often compared to partial crowns, overlays are very different from crowns. The main difference lies in the preparation of the tooth. Where inlays, onlays, overlays and pinlays are concerned, they fit in the remaining a part of the tooth like a piece of jigsaw puzzle. Unlike crowns, they require less preparation of the tooth and therefore keep more of the natural tooth structure intact.
Pinlays are characterized by the use of pins to strengthen retention, i.e. any inlay, onlay and overlay which are braced by pins are called pinlays. These pins may be inserted at the edges of the teeth or parallel to the grooves. It is important that the base of the pin should lie in tooth surface that is free of damage.
Benefits and Drawbacks
Inlays and onlays are contraindicated under certain conditions. In cases where facial and inner surface of the tooth is damaged or there is high level of decay, then crowns are more suitable than inlays and onlays.
Other than keeping more of the original tooth structure, inlays, onlays and overlays offer additional benefits. As these are custom made, they offer a much better fit than other restorations. They can also be used for tight spaces, that is, for cavities between the teeth.
As there is minimal preparation of the tooth, the facial and lingual enamel is retained offering better contouring at the gum line. This, in turn, is useful in keeping soft tissues healthy. The customized fitting allows for excellent interproximal contact, making repeated decay almost impossible. Though inlays, onlays, overlays and pinlays are more expensive than direct fillings, the benefits they offer in terms of longevity and maintenance of dental health compensates for the extra cost.