Inlays and Onlays are necessary if a tooth’s original structure is too compromised to support a filling. They are fabricated in a laboratory, and are not placed right away like a filling. The dentist takes impressions of the teeth and the restoration is then fabricated to match the part of the tooth it will replace. The restoration is then cemented in a week or two later. Inlays and Onlays provide added strength to a tooth, similar to a crown, and can last several years.