Also known as indirect fillings, inlays and onlays made from porcelain or composite materials are a long-lasting yet cosmetic way to provide a “filling” to teeth with tooth decay or similar structural damage. Whereas dental fillings are molded into place within the mouth during a dental visit, inlays and onlays are created in a dental laboratory before being fitted and adhesively bonded into place by your dentist.
Source: http://www.yourdentistryguide.com