The product used for dental inlay-onlay procedures are custom made out of composite materials that are very gentle to the tooth that it is placed on. It can be prone to wear and tear and discoloration, as are normal teeth. There is also gold products and tooth-colored porcelain which is a very natural looking option. When permanently adhered to the tooth, it will last a very long time.
Direct and indirect restorations can be done for a patient. Direct restorations are done in a dental office by the staff there, while indirect restorations are done at a lab off site.
Indirect onlays are done by having an impression made of the cleaned, affected tooth. That impression is sent to a lab and the product is made within a few weeks. Usually, a temporary filling is used to get you to that next appointment. The direct onlay option works the same way, but it is created in the dental office.