An inlay is a type of dental restoration that is applied in between the cusps (the ridges) of your teeth. Like a lake in the midst of mountains, it sits below the crests of your teeth.
An onlay is more like a glacier. It covers the entire tooth, including the cusps. It sits on top of the tooth.
For both of these procedures, porcelain is often recommended, especially if the tooth is visible in the smile. Porcelain blends in far better than metals and other treatments – it looks more like a natural tooth.
In some cases a metal inaly or onlay will be the option of treatment for the tooth and patient and in that case a gold metal will be used.