What are Inlays and Onlays?
Inlays
Traditionally, inlays replace a small amount of tooth structure left by a cavity, just as fillings do. They filled and sealed the tooth but were made only of gold. Inlays today are made of tooth-colored material such as ceramic, porcelain, or a specialized dental composite.
The inlay consists of the tooth-colored material and bonding, a clear fluid material, to attach the inlay to the tooth. As explained by the American College of Prosthodontists, "Using a clear fluid version of this material to seal the exposed surfaces of the teeth decreases sensitivity to temperature changes and certain types of foods." The bonding material is also tooth-colored and may be used to improve the color and appearance of stained or discolored teeth.
Onlays
Onlays are similar to inlays in that they fill a missing hole caused by a cavity, but onlays extend onto the chewing surface of a tooth to replace one or more cusps. Traditionally, they were also only made of gold, but tooth-colored onlays have made an appearance in dentistry. An onlay is considered a more effective option for patients with large cavities or the decayed area expands over the top of the tooth.
The process of inlays and onlays both involve bonding material to attach and seal it to the tooth. In both treatments, the bonding material may actually improve the strength of the tooth.
Inlay or Filling
Inlays are a cosmetic treatment that can replace old fillings. Increasingly, patients have had the option to choose between a filling or inlay when treating a cavity. We use an impression of the cavity in question to ensure the inlay is the exact size and shape, as opposed to other options that may weaken the tooth. In this way, the cemented inlay strengthens the tooth rather than weakening it.
As inlays become more popular because of their appearance, fillings are hardly ever requested. However, a dentist may resort to a filling for cases in which the patient is allergic to the inlay material used. In many cases, special dental material can be used as an inlay to provide the patient with the highest level of comfort.
Onlay vs. Crown
An onlay is generally used when a patient has a small hole that is only a tad larger than an inlay or old filling. In most cases, an onlay can cover the cavity hole and surrounding area. Onlays are a less aggressive restoration treatment than crowns as a smaller amount of tooth structure needs to be removed.
On the other hand, crowns are caps or covers used to restore the function and appearance of a tooth but replace the tooth itself. According to the article on caps and crowns, "Crowns are indicated for teeth with very large fillings, teeth that have had a root canal, fractured teeth, worn teeth due to grinding, and misshapen and/or discolored teeth." The key distinguishing factor a dentist will use to determine the right choice for a patient is the size of the cavity.