An onlay is a porcelain or metal restoration that protects a broken down or fractured tooth from further deterioration. It works like a bottle cap cover to hold a tooth together. An onlay is necessary when a tooth has more than one third of its structure lost to decay or fracture, when the tooth is cracked, or when a root canal therapy has been performed. Onlays may also be placed for cosmetic reasons or to correct a misshapen tooth.

Life Span

An onlay can last fifteen- twenty years or longer if properly cared for. The important thing to remember is that decay can occur even if the tooth is covered with an onlay. The margin where the onlay meets the tooth must be kept clean or decay can take hold and undermine the restoration. Proper oral hygiene, use of fluoride, and regular dental checkups will minimize the problem.


The major advantage of an onlay when compared to a crown is that more of a patient’s natural tooth structure is retained. The margins are usually high up on the side of the tooth where they are easily cleaned. Since less tooth structure is removed in the preparation process, there is less likelihood of post-operative sensitivity. When an onlay is placed instead of a large filling, the restoration is stronger and longer lasting since it involves custom fit laboratory procedures with materials that are prefabricated and hardened to withstand chewing pressure for years.


The major disadvantage of an onlay is that many insurance companies choose only to reimburse to the least expensive procedure and will pay only the amount for an amalgam filling. While there may be out-of-pocket costs to the patient, the upside is that in the long run the restoration will be more durable and will not need replacement as soon as a filling.

Possible Complications to Onlays

Sensitivity or Pain

Some sensitivity is normal for twenty-four hours. If it persists or if severe pain is experienced, we would need to know. Because onlays are placed on teeth that have suffered trauma through decay or fracture, there is a possibility that the tooth could abscess in the future, even though there may be no indication at time of placement.

"High" feeling

An onlay may need occlusal adjustment after placement. Because a patient is anesthetized in the office, he or she may not feel a discrepancy in the bite until later when the anesthetic wears off. If an onlay does not feel right when chewing, a patient should return to the office for an adjustment as soon as it is detected. Failure to correct this issue can result in unnecessary discomfort for the patient.